@article{temizer_broman_nori_reynolds_kumar_narayan_2024, title={Enhanced optical transmittance and room temperature ferromagnetism in Al-doped zinc oxide epitaxial films}, volume={14}, ISSN={["2158-3226"]}, DOI={10.1063/5.0224007}, abstractNote={We present a systematic investigation of the detailed structural, optical and magnetic properties of ZnO thin films deposited by pulsed laser deposition as a function of varying Al doping from 0% to 5%. The observed features can be associated with strain introduced into the ZnO lattice by the incorporation of Al. Enhanced optical transmittance values close to 95% were achieved in Al-doped ZnO epitaxial films deposited on sapphire substrates. In addition, these films exhibit robust ferromagnetic properties at room temperature with saturation magnetization that varies from 143 to 63 emu/cm3 for Al dopant concentrations from 0% to 5%. It is demonstrated that the saturation magnetization is related to the strain introduced into the lattice with increased Al doping.}, number={10}, journal={AIP ADVANCES}, author={Temizer, Namik K. and Broman, Melanie and Nori, Sudhakar and Reynolds, Lewis and Kumar, Dhananjay and Narayan, Jagdish}, year={2024}, month={Oct} }
 @article{joshi_narayan_narayan_2024, title={Multifunctional carbon-based nanostructures (CBNs) for advanced biomedical applications - a perspective and review}, volume={10}, ISSN={["2633-5409"]}, url={https://doi.org/10.1039/D3MA00636K}, DOI={10.1039/d3ma00636k}, abstractNote={Carbon-based nanostructures (CBNs) have attracted immense attention from biomedical researchers due to their unique combination of extraordinary mechanical, thermal, electrical, and optical properties.}, journal={MATERIALS ADVANCES}, author={Joshi, Naveen Narasimhachar and Narayan, Jagdish and Narayan, Roger}, year={2024}, month={Oct} }
 @article{pethe_sahoo_ganesan_meyer iii_sun_narayan_paranthaman_2024, title={Novel Q-Carbon Anodes for Sodium-Ion Batteries}, volume={14}, ISSN={["2076-3417"]}, url={https://www.mdpi.com/2076-3417/14/22/10679}, DOI={10.3390/app142210679}, abstractNote={The lack of a standard anode for sodium-ion batteries (SIBs) has greatly hindered their applications. Herein, we show that a novel phase of carbon, namely Q-carbon, is an effective anode material for sodium-ion batteries. The Q-carbon, which is a metastable phase of carbon consisting of about 80% sp3- and 20% sp2-bonded carbon, is synthesized by nonequilibrium pulsed laser annealing and arc-discharge methods. Two types of Q-carbons, Q1 and Q2, were evaluated as anode material for SIBs. Q1 had a slow quench and was used as the control, whereas Q2 was Q-carbon with a rapid quenching. Q1 exhibits a high initial columbic efficiency of 81% and a low-capacity retention of less than 60%, whereas Q2 has a low initial columbic efficiency of 58% and a high-capacity retention of 81%. Q2 exhibits a stable capacity of 168 mAh·g−1 at a cycling rate of C/3 (124 mA·g−1), which is comparable to other hard carbon anodes reported in the literature. This unique synthesis method opens a pathway for the further tuning of Q-carbon with higher trapping/charging of Na+ ions in improved SIBs.}, number={22}, journal={APPLIED SCIENCES-BASEL}, author={Pethe, Saurabh Prakash and Sahoo, Siba Sundar and Ganesan, Arvind and Meyer III, Harry M. and Sun, Xiao-Guang and Narayan, Jagdish and Paranthaman, Mariappan Parans}, year={2024}, month={Nov} }
 @article{narayan_2024, title={Path for Room-Temperature Superconductivity in Q-Carbon-Related Materials}, volume={10}, ISSN={["2311-5629"]}, url={https://www.mdpi.com/2311-5629/10/1/14}, DOI={10.3390/c10010014}, abstractNote={We present the atomic structures and nonequilibrium synthesis of a new class of materials, where the basic structural unit is a diamond tetrahedron. When units of one, two, and three tetrahedra are randomly packed, we create distinct phases of amorphous Q-carbon. Four tetrahedra in two adjacent layers lead to crystalline diamond lattice, which has four missing tetrahedra alternately. When these four missing tetrahedra are filled, we create subunit cell of crystalline Q-diamond. Theoretical calculations show that the superconducting transition temperature (Tc) in 50 atomic % B-doped Q-diamond can reach room temperature at ambient pressures. This is consistent with our earlier results using low-loss EELS measurements in 50 atomic % B-doped Q-carbon, which had mostly amorphous QB3 phase mixed with some crystalline Q-diamond phase. These EELS results showed that the Tc for these samples was between 90 K and 300 K. Theoretical calculations of density of states, Eliashberg function, electron–phonon interaction parameter, and root-mean-square and logarithmic average of frequency in crystalline Q-diamond show Tc in the range of 268 K to 300 K, which is in complete agreement with our EELS results in QB3.}, number={1}, journal={C-JOURNAL OF CARBON RESEARCH}, author={Narayan, Jagdish}, year={2024}, month={Mar} }
 @article{joshi_shukla_khosla_vanderwal_stafslien_narayan_narayan_2024, title={Q-carbon as an emergent surface coating material for antimicrobial applications}, volume={791}, ISSN={["1879-2731"]}, url={https://doi.org/10.1016/j.tsf.2024.140227}, DOI={10.1016/j.tsf.2024.140227}, abstractNote={Q-carbon, an allotrope of carbon, exhibits exciting functional properties and robust mechanical strength. We propose that the surface of the Q-carbon can be functionalized by doping it with silicon to enhance its performance as a potential implant material. As such, a coating of silicon-doped Q-carbon (Si-Q-carbon) is shown to minimize the formation of biofilm, thus reducing the risk of microbial infection. We report the formation of Si-Q-carbon coatings of varied thicknesses (10 nm and 20 nm) through the plasma-enhanced chemical vapor deposition technique. The surface composition and the bonding characteristics of the thin films were evaluated by Raman spectroscopy, XPS, and EELS studies, which showed that the thinnest sample (10 nm) has a high sp3 content of ∼85%. Furthermore, wettability and surface energy calculations were undertaken to investigate the surface characteristics of the coatings. The 10 nm sample was found to be more hydrophilic with a water contact angle of 75.3° (± 0.6°). The antibacterial activity of Si-Q-carbon coatings was investigated using a Staphylococcus epidermidis agar plating technique, and the adhesion of bacteria was explained in terms of the surface properties of the thin films. We demonstrate that the Si-Q-carbon coating with the highest sp3 content is hydrophilic and showed a 57% reduction in adhered biofilm relative to a glass control. We envisage the potential application of Q-carbon in arthroplasty devices with enhanced mechanical strength and resistance to periprosthetic joint infections.}, journal={THIN SOLID FILMS}, author={Joshi, Naveen and Shukla, Shubhangi and Khosla, Nayna and Vanderwal, Lyndsi and Stafslien, Shane and Narayan, Jagdish and Narayan, Roger J.}, year={2024}, month={Feb} }
 @article{haque_taqy_narayan_2024, title={Recent Progress in Cubic Boron Nitride (c-BN) Fabrication by Pulsed Laser Annealing for Optoelectronic Applications}, volume={6}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-024-11171-0}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Haque, Ariful and Taqy, Saif and Narayan, Jagdish}, year={2024}, month={Jun} }
 @article{haque_liu_taqy_narayan_2023, title={Cost-Effective Synthesis of Diamond Nano-/Microstructures from Amorphous and Graphitic Carbon Materials: Implications for Nanoelectronics}, volume={6}, ISSN={["2574-0970"]}, DOI={10.1021/acsanm.2c05098}, abstractNote={The synthesis of diamonds with different microstructures is important for various applications including nanoelectronic devices where diamonds can be implemented as heat spreaders. Here we report the synthesis of functional diamond microstructures and coatings, including diamond microfibers, microspheres, tubes, and large-area thin film, using amorphous and graphitic carbon precursors by hot filament chemical vapor deposition. The characteristics of microstructures depend upon initial carbon precursors and their laser annealing pretreatments. Low-cost and abundant carbon precursors act as diamond nucleation sites and accelerate diamond growth, while laser annealing can further promote the nucleation and growth of diamond. As a result, carbon microfibers are converted to diamond microfibers, while large diamond microspheres are formed from multipulse laser-annealed carbon microfibers. Both of the diamond structures consist of 5-fold twinned microcrystallites. Highly dense and phase-pure diamond films are observed using porous carbon seed, and individual diamond tubes with porous walls are obtained by using carbon nanotube hollow fibers. The electron backscatter diffraction analysis confirms the diamond cubic lattice structure, while sharp diamond peaks (1331–1333 cm–1) in Raman spectra demonstrate the excellent diamond quality of prepared diamond microstructures.}, number={8}, journal={ACS APPLIED NANO MATERIALS}, author={Haque, Ariful and Liu, Yanming and Taqy, Saif and Narayan, Jay}, year={2023}, month={Apr}, pages={6488–6495} }
 @article{khosla_narayan_narayan_2023, title={Laser-assisted formation of 3c-SiC and continuous diamond growth using Si-Q carbon on (100) silicon}, volume={12}, ISSN={["2044-5326"]}, DOI={10.1557/s43578-023-01264-7}, abstractNote={The formation of 3c-SiC is of interest due to potential applications in the semiconductor industry; however, there are difficulties in obtaining 3c-SiC by conventional methods. Being a metastable phase, non-equilibrium growth conditions are favorable in the growth process. This paper reports the formation of nano-sized 3c-SiC by nanosecond laser annealing of Si–Q-carbon layers on the silicon (100), which is confirmed by its characteristic LO and TO peaks in the Raman spectra. We also show that the traditional HFCVD technique results in the 6H-polytype instead, as confirmed by SEM, Raman spectroscopy, and EBSD. Further, we investigate the role of these phases on the nucleation of heteroepitaxial diamond on a Si (100) substrate. We show that these phases as interlayers enhance the diamond growth significantly. The HRSTEM studies were performed to understand the interfacial structure and phase responsible for high diamond nucleation. These findings are significant for 3c-SiC and diamond electronics applications. Graphical abstract}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Khosla, Nayna and Narayan, Jagdish and Narayan, Roger}, year={2023}, month={Dec} }
 @article{gupta_narayan_2023, title={Laser-induced synthesis of cubic BN nanoneedles: a new approach to fabricating nanomaterials for advanced applications}, volume={25}, ISSN={["1572-896X"]}, DOI={10.1007/s11051-023-05897-x}, number={12}, journal={JOURNAL OF NANOPARTICLE RESEARCH}, author={Gupta, Siddharth and Narayan, Jagdish}, year={2023}, month={Dec} }
 @article{khosla_narayan_narayan_sun_paranthaman_2023, title={Microstructure and defect engineering of graphite anodes by pulsed laser annealing for enhanced performance of lithium-ion batteries}, volume={205}, ISSN={["1873-3891"]}, url={https://doi.org/10.1016/j.carbon.2023.01.009}, DOI={10.1016/j.carbon.2023.01.009}, abstractNote={Nanosecond pulsed laser annealing significantly improves cyclability and current carrying capacity of lithium-ion batteries (LIBs). This improvement is achieved by engineering of microstructure and defect contents present in graphite in a controlled way by using pulsed laser annealing (PLA) to increase the number density of Li+ ion trapping sites. The PLA treatment causes the following changes: (1) creates surface steps and grooves between the grains to improve Li+ ion charging and intercalation rates; (2) removes inactive polyvinylidene difluoride (PVDF) binder from the top of graphite grains and between the grains which otherwise tends to block the Li+ migration; and (3) produces carbon vacancies in (0001) planes which can provide Li+ charging sites. From X-ray diffraction data, we find upshift in diffraction peak or reduction in planar spacing, from which vacancy concentration was estimated to be about 1.0%, which is higher than the thermodynamic equilibrium concentration of vacancies. The laser treatment creates single and multiple C vacancies which provide sites for Li+ ions, and it also produces steps and grooves for Li+ ions to enter the intercalating sites. It is envisaged that the formation of these sites enhances Li+ ion absorption during charge and discharge cycles. The current capacity increases from an average 360 mAh/g to 430 mAh/g, and C–V shows significant reduction in SEI layer formation after the laser treatment. If the vacancy concentration is too high and charge-discharge cycles are long, then trapping of electrons by Li+ may occur, which can lead to Li0 formation and Li plating causing reduction in current capacity.}, journal={CARBON}, author={Khosla, Nayna and Narayan, Jagdish and Narayan, Roger and Sun, Xiao-Guang and Paranthaman, Mariappan Parans}, year={2023}, month={Mar}, pages={214–225} }
 @article{khosla_narayan_narayan_sun_paranthaman_2023, title={Nanosecond Laser Annealing of NMC 811 Cathodes for Enhanced Performance}, volume={170}, ISSN={["1945-7111"]}, url={https://doi.org/10.1149/1945-7111/acc27d}, DOI={10.1149/1945-7111/acc27d}, abstractNote={Improved performance of lithium-ion batteries (LIBs) plays a critical role in the future of next- generation battery applications. Nickel-rich layered oxides such as LiNi0.8Mn0.1Co0.1O2 (NMC 811), are popular cathodes due to their high energy densities. However, they suffer from high surface reactivity, which results in the formation of Li2CO3 passive layer. Herein, we show the role of nanosecond pulsed laser annealing (PLA) in improving the current capacity and cycling stability of LIBs by reducing the carbonate layer, in addition to forming a protective LiF layer and manipulating the NMC 811 microstructures. We use high-power nanosecond laser pulses in a controlled way to create nanostructured surface topography which has a positive impact on the capacity retention and current capacity by providing an increased active surface area, which influences the diffusion kinetics of lithium-ions in the electrode materials during the battery cycling process. Advanced characterizations show that the PLA treatment results in the thinning of the passive Li2CO3 layer, which is formed on as-received NMC811 samples, along with the decomposition of excess polyvinylidene fluoride (PVDF) binder. The high-power laser interacts with the decomposed binder and surface Li+ to form LiF phase, which acts as a protective layer to prevent surface reactive sites from initiating parasitic reactions. As a result, the laser treated cathodes show relative increase of the current capacity of up to 50%, which is consistent with electrochemical measurements of LiB cells.}, number={3}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Khosla, Nayna and Narayan, Jagdish and Narayan, Roger and Sun, Xiao-Guang and Paranthaman, M. Parans}, year={2023}, month={Mar} }
 @unpublished{path for near room-temperature superconductivity in q-carbon related materials, DOI={10.20944/preprints202306.1385.v1}, abstractNote={We present atomic structures and nonequilbrium synthesis of new class of materials, where the basic structural unit is a diamond tetrahedron. When units of one, two, and three tetrahedra are randomly packed, we create distinct phases of amorphous Q-carbon. Four tetrahedra in two adjacent layers lead to crystalline diamond lattice, which has four missing tetrahedra alternately. When these four missing tetrahedra are filled, we create subunit cell of crystalline Q-diamond. Theoretical calculations show that superconducting transition temperature (Tc) in 50 atomic % B-doped Q-diamond can reach near room temperature at ambient pressures. This is consistent with our earlier results using low-loss EELS measurements in 50 atomic % B-doped Q-carbon, which had mostly amorphous QB3 phase mixed with some crystalline Q-diamond phase. These EELS results showed that the Tc for these samples was in between 90K and 300K. Theoretical calculations of density of states, Eliashberg function, electron-phonon interaction parameter, and root-mean-square and logarithmic average of frequency in crystalline Q-diamond show Tc in the range of 268K to 300K, which is in a complete agreement with our EELS results in QB3.} }
 @unpublished{path for room-temperature superconductivity in q-carbon related materials, DOI={10.20944/preprints202306.1385.v2}, abstractNote={We present atomic structures and nonequilbrium synthesis of new class of materials, where the basic structural unit is a diamond tetrahedron. When units of one, two, and three tetrahedra are randomly packed, we create distinct phases of amorphous Q-carbon. Four tetrahedra in two adjacent layers lead to crystalline diamond lattice, which has four missing tetrahedra alternately. When these four missing tetrahedra are filled, we create subunit cell of crystalline Q-diamond. Theoretical calculations show that superconducting transition temperature (Tc) in 50 atomic % B-doped Q-diamond can reach near room temperature at ambient pressures. This is consistent with our earlier results using low-loss EELS measurements in 50 atomic % B-doped Q-carbon, which had mostly amorphous QB3 phase mixed with some crystalline Q-diamond phase. These EELS results showed that the Tc for these samples was in between 90K and 300K. Theoretical calculations of density of states, Eliashberg function, electron-phonon interaction parameter, and root-mean-square and logarithmic average of frequency in crystalline Q-diamond show Tc in the range of 268K to 300K, which is in a complete agreement with our EELS results in QB3.} }
 @article{narayan_sahoo_joshi_narayan_2023, title={Synthesis and novel properties of Q-silicon (January 2023)}, volume={11}, ISSN={["2166-3831"]}, url={http://dx.doi.org/10.1080/21663831.2023.2224396}, DOI={10.1080/21663831.2023.2224396}, abstractNote={We report the discovery of Q-silicon with an atomic density of 60% higher than crystalline silicon while keeping the bonding characteristics the same as normal silicon. Distinct amorphous phases are created, when one, two, or three tetrahedra are randomly packed, and a crystalline phase of Q-silicon is formed when subunit cells are arranged along <110> directions with alternate holes. Nanosecond laser melting of amorphous silicon in an undercooled state and quenching have created Q-silicon with robust ferromagnetism compared to the diamagnetism of silicon. The blocking temperature of Q-silicon is estimated to be over 400 K, thus opening a new frontier for spin-based computing and atomic-level storage. GRAPHICAL ABSTRACT IMPACT STATEMENT The discovery of Q-silicon having robust RT ferromagnetism will open a new frontier in atomic-scale spin-based devices and functional integration with nanoelectronics. Other properties of interest include enhanced hardness and superconductivity.}, number={8}, journal={MATERIALS RESEARCH LETTERS}, publisher={Informa UK Limited}, author={Narayan, Jagdish and Sahoo, Siba Sundar and Joshi, Naveen and Narayan, Roger}, year={2023}, month={Aug}, pages={688–696} }
 @article{joshi_shukla_gupta_joshi_narayan_narayan_2023, title={Synthesis of laser-patterned MoS2 nanoneedles for advanced electrochemical sensing}, volume={6}, ISSN={["2159-6867"]}, url={http://dx.doi.org/10.1557/s43579-023-00381-y}, DOI={10.1557/s43579-023-00381-y}, abstractNote={We describe a novel excimer laser-based route for the fabrication of crystalline MoS2 nanoneedles. Laser annealing of MoS2 thin films at a low energy density of 0.08 Jcm−2 resulted in a closed-pack structure with low defects and excellent conductivity due to melting and rapid quenching. A further increase in laser annealing energy density resulted in the formation of MoS2 nano-needles. This structure of MoS2 was found to have a remarkable reduction ability for H2O2 at − 0.14 V over a wide linear range; a low detection limit (0.45 nM (S/N = 3)) and sensitivity of 2.38 μA/mM cm−2 were demonstrated.}, number={4}, journal={MRS COMMUNICATIONS}, publisher={Springer Science and Business Media LLC}, author={Joshi, Pratik and Shukla, Shubhangi and Gupta, Siddharth and Joshi, Naveen and Narayan, Jagdish and Narayan, Roger}, year={2023}, month={Jun} }
 @article{narayan_narayan_2022, title={Discovery of Double Helix and Impact on Nanoscale to Mesoscale Crystalline Structures}, volume={7}, ISSN={["2470-1343"]}, DOI={10.1021/acsomega.2c03501}, abstractNote={Screw dislocations play a significant role in the growth of crystalline structures by providing a continuous source of surface steps which represent available sites for crystal growth. Here, we show that pure screw dislocations can become helical from the absorption of defects (e.g., vacancies) and develop an attractive interaction with another helical dislocation to form a double helix of screw dislocations. These single and double helices of screw dislocations can result in the formation of interesting nanostructures with large Eshelby twists. We have previously proposed the formation of a double helix of screw dislocations to explain large Eshelby twists in crystalline nanostructures (Mater. Res. Lett.2021, 9, 453−457). We now show direct evidence for the formation of a double helix during thermal annealing of screw dislocations. The large Burgers vectors associated with these dislocations are used to explain the presence of large Eshelby twists in PbSe and PbS (NaCl cubic structure) and InP and GeS (wurtzite hexagonal structure) nanowires. These single- and double-helix screw dislocations can also combine to create even larger super Burgers vectors. These large effective Burgers also unravel the mechanism for the formation of nanopipes and micropipes with hollow cores and nanotubes with Eshelby twists in technologically important materials such as SiC, GaN, and ZnO that are utilized in a variety of advanced solid-state devices.}, number={29}, journal={ACS OMEGA}, author={Narayan, Jagdish and Narayan, Roger}, year={2022}, month={Jul}, pages={25853–25859} }
 @article{riley_yang_liu_skoog_narayan_narayan_2022, title={Effect of oxygen and fluorine plasma surface treatment of silicon-incorporated diamond-like carbon coatings on cellular responses of mouse fibroblasts}, volume={6}, ISSN={["1744-7402"]}, DOI={10.1111/ijac.14107}, abstractNote={AbstractThe surface chemistry of silicon‐incorporated diamond‐like carbon (Si‐DLC) was tailored utilizing oxygen and fluorine plasma treatments. Successful anchoring of oxygen and fluorine functional groups to the surface of Si‐DLC was verified using X‐ray photoelectron spectroscopy. The impact of surface modification of Si‐DLC on hydrophobicity was correlated with the viability of L929 mouse fibroblasts. The confocal microscopy and viability results indicated that oxygen‐treated Si‐DLC showed increased cell viability compared to untreated Si‐DLC and fluorine‐treated Si‐DLC samples 5 days after seeding. The increased cell viability was correlated with the conversion of the hydrophobic surface of Si‐DLC into a hydrophilic surface by oxygen plasma treatment.}, journal={INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY}, author={Riley, Parand R. and Yang, Kai-Hung and Liu, Yizhong and Skoog, Shelby A. and Narayan, Jagdish and Narayan, Roger J.}, year={2022}, month={Jun} }
 @article{joshi_shukla_gupta_riley_narayan_narayan_2022, title={Excimer Laser Patterned Holey Graphene Oxide Films for Nonenzymatic Electrochemical Sensing}, volume={14}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c09096}, DOI={10.1021/acsami.2c09096}, abstractNote={The existence of point defects, holes, and corrugations (macroscopic defects) induces high catalytic potential in graphene and its derivatives. We report a systematic approach for microscopic and macroscopic defect density optimization in excimer laser-induced reduced graphene oxide by varying the laser energy density and pulse number to achieve a record detection limit of 7.15 nM for peroxide sensing. A quantitative estimation of point defect densities was obtained using Raman spectroscopy and confirmed with electrochemical sensing measurements. Laser annealing (LA) at 0.6 J cm-2 led to the formation of highly reduced graphene oxide (GO) by liquid-phase regrowth of molten carbon with the presence of dangling bonds, making it catalytically active. Hall-effect measurements yielded a mobility of ∼200 cm2 V-1 s-1. An additional increase in the number of pulses at 0.6 J cm-2 resulted in deoxygenation through the solid-state route, leading to the formation of holey graphene structure. The average hole size showed a hierarchical increase, with the number of pulses characterized with multiple microscopy techniques, including scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The exposure of edge sites due to high hole density after 10 pulses supported the formation of proximal diffusion layers, which led to facile mass transfer and improvement in the detection limit from 25.4 mM to 7.15 nM for peroxide sensing. However, LA at 1 J cm-2 with 1 pulse resulted in a high melt lifetime of molten carbon and the formation of GO characterized by a high resistivity of 3 × 10-2 Ω-cm, which was not ideal for sensing applications. The rapid thermal annealing technique using a batch furnace to generate holey graphene results in structure with uneven hole sizes. However, holey graphene formation using the LA technique is scalable with better control over hole size and density. This study will pave the path for cost-efficient and high-performance holey graphene sensors for advanced sensing applications.}, number={32}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Joshi, Pratik and Shukla, Shubhangi and Gupta, Siddharth and Riley, Parand R. and Narayan, Jagdish and Narayan, Roger}, year={2022}, month={Aug}, pages={37149–37160} }
 @article{gupta_joshi_sachan_narayan_2022, title={Fabricating Graphene Oxide/h-BN Metal Insulator Semiconductor Diodes by Nanosecond Laser Irradiation}, volume={12}, ISSN={["2079-4991"]}, url={https://doi.org/10.3390/nano12152718}, DOI={10.3390/nano12152718}, abstractNote={To employ graphene’s rapid conduction in 2D devices, a heterostructure with a broad bandgap dielectric that is free of traps is required. Within this paradigm, h-BN is a good candidate because of its graphene-like structure and ultrawide bandgap. We show how to make such a heterostructure by irradiating alternating layers of a-C and a-BN film with a nanosecond excimer laser, melting and zone-refining constituent layers in the process. With Raman spectroscopy and ToF-SIMS analyses, we demonstrate this localized zone-refining into phase-pure h-BN and rGO films with distinct Raman vibrational modes and SIMS profile flattening after laser irradiation. Furthermore, in comparing laser-irradiated rGO-Si MS and rGO/h-BN/Si MIS diodes, the MIS diodes exhibit an increased turn-on voltage (4.4 V) and low leakage current. The MIS diode I-V characteristics reveal direct tunneling conduction under low bias and Fowler-Nordheim tunneling in the high-voltage regime, turning the MIS diode ON with improved rectification and current flow. This study sheds light on the nonequilibrium approaches to engineering h-BN and graphene heterostructures for ultrathin field effect transistor device development.}, number={15}, journal={NANOMATERIALS}, author={Gupta, Siddharth and Joshi, Pratik and Sachan, Ritesh and Narayan, Jagdish}, year={2022}, month={Aug} }
 @article{khosla_narayan_2022, title={Fabrication of Q-Carbon Nanostructures, Diamond and Their Composites with Wafer-Scale Integration}, volume={12}, ISSN={["2073-4352"]}, url={https://www.mdpi.com/2073-4352/12/5/615}, DOI={10.3390/cryst12050615}, abstractNote={We report the formation of Q-carbon nanolayers, Q-carbon nanoballs, nanodiamonds, microdiamonds, and their composites by controlling laser and substrate variables. The choice of these parameters is guided by the SLIM (simulation of laser interactions with materials) computer modeling. For a constant film thickness and initial sp3 content, we obtain different microstructures with increasing pulse energy density as a result of different quenching rate and undercooling. This is related to decreasing undercooling with increasing pulse energy density. The structure of thin film Q-carbon evolves into Q-carbon nanoballs with the increase in laser annealing energy density. These Q-carbon nanoballs interestingly self-organize in the form of rings with embedded nanodiamonds to form Q-carbon nanoballs/diamond composites. We form high quality, epitaxial nano, and micro diamond films at a higher energy density and discuss a model showing undercooling and quenching rate generating a pressure pulse, which may play a critical role in a direct conversion of amorphous carbon into Q-carbon or diamond or their composites. This ability to selectively tune between diamond or Q-carbon or their composites on a single substrate is highly desirable for a variety of applications ranging from protective coatings to nanosensing and field emission to targeted drug delivery. Furthermore, Q-carbon nanoballs and nanodiamonds are utilized as seeds to grow microdiamond films by HFCVD. It is observed that the Q-carbon nanoballs contain diamond nuclei of critical size, which provide available nucleation sites for diamond growth, leading to stress-free, adherent, and denser films, which are needed for a variety of coating applications.}, number={5}, journal={CRYSTALS}, publisher={MDPI AG}, author={Khosla, Nayna and Narayan, Jagdish}, year={2022}, month={May} }
 @article{riley_joshi_khosla_narayan_narayan_2022, title={Formation of Q-carbon with wafer scale integration}, volume={196}, ISSN={["1873-3891"]}, url={https://doi.org/10.1016/j.carbon.2022.06.003}, DOI={10.1016/j.carbon.2022.06.003}, abstractNote={We describe the formation of highly uniform Quenched-carbon (Q-carbon) layers by plasma-enhanced chemical vapor deposition (PECVD) followed by low-energy Ar+ ion bombardment to achieve wafer-scale integration of Q-carbon films. After PECVD, 9 nm and 20 nm thick silicon-doped diamond-like carbon (Si-DLC) films showed complete conversion into Q-carbon using 250eV Ar+ ions via negative biasing. However, this conversion was only partial for 30 nm thick films. Detailed EELS, XPS, Raman, and EDS studies were carried out to confirm the formation of Q-carbon by this method. We discuss the mechanism of Q-carbon formation as a result of low-energy ion bombardment during PECVD of thin films. These ions during negative biasing are energetic enough to create Frenkel defects, which support the conversion of the three-fold coordinated sp2 carbon units in as-deposited carbon into sp3 bonded five-atom tetrahedron units in Q-carbon. This process enhances the atomic number density and fraction of sp3 bonded carbon. These diamond tetrahedra are randomly packed and provide easy nucleation sites for diamond. If the underlying substrate can provide an epitaxial template for diamond growth via domain matching epitaxy, then wafer-scale growth of diamond epitaxial films can be achieved for wafer-scale integration and next-generation novel device manufacturing from diamond-related materials.}, journal={CARBON}, author={Riley, Parand R. and Joshi, Pratik and Khosla, Nayna and Narayan, Roger J. and Narayan, Jagdish}, year={2022}, month={Aug}, pages={972–978} }
 @article{cui_khosla_lai_narayan_manthiram_2022, title={Laser-Assisted Surface Lithium Fluoride Decoration of a Cobalt-Free High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode for Long-Life Lithium- Ion Batteries}, volume={12}, ISSN={["1944-8252"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85145292920&partnerID=MN8TOARS}, DOI={10.1021/acsami.2c18918}, abstractNote={High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising next-generation cathode material due to its structural stability, high operation voltage, and low cost. However, the cycle life of LNMO cells is compromised by detrimental electrode-electrolyte reactions, chemical crossover, and rapid anode degradation. Here, we demonstrate that the cycling stability of LNMO can be effectively enhanced by a high-energy laser treatment. Advanced characterizations unveil that the laser treatment induces partial decomposition of the polyvinylidene fluoride binder and formation of a surface LiF phase, which mitigates electrode-electrolyte side reactions and reduces the generation of dissolved transition-metal ions and acidic crossover species. As a result, the solid electrolyte interphase of the graphite counter electrode is thin and is composed of fewer electrolyte decomposition products. This work demonstrates the potential of laser treatment in tuning the surface chemistry of cathode materials for lithium-ion batteries.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Cui, Zehao and Khosla, Nayna and Lai, Tianxing and Narayan, Jagdish and Manthiram, Arumugam}, year={2022}, month={Dec} }
 @article{joshi_riley_denning_shukla_khosla_narayan_narayan_2022, title={Laser-patterned carbon coatings on flexible and optically transparent plastic substrates for advanced biomedical sensing and implant applications}, volume={1}, ISSN={["2050-7534"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85125716163&partnerID=MN8TOARS}, DOI={10.1039/d1tc05176h}, abstractNote={Plasma and laser-based processing for tailoring DLC thin film properties for state-of-the-art wearable sensing applications.}, number={8}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, publisher={Royal Society of Chemistry (RSC)}, author={Joshi, Pratik and Riley, Parand R. and Denning, Warren and Shukla, Shubhangi and Khosla, Nayna and Narayan, Jagdish and Narayan, Roger}, year={2022}, month={Jan} }
 @article{narayan_khosla_2022, title={Self-organization of amorphous Q-carbon and Q-BN nanoballs}, volume={192}, ISSN={["1873-3891"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85125815590&partnerID=MN8TOARS}, DOI={10.1016/j.carbon.2022.03.003}, abstractNote={This paper reports for the first time the formation and self-organization of amorphous Q-carbon and Q-BN nanoballs. This is accomplished by nanosecond laser melting of carbon and BN layers, respectively, in a highly undercooled state and subsequent rapid cooling at normal pressures in air. The size of these Q-carbon and Q-BN nanoballs having a uniform size can be varied from 5 to 100 nm, and self-organized along rings and strings by manipulating laser, carbon film, and substrate parameters. It is envisaged that self-organization is promoted by the undercooling and it occurs along strings and rings, which are formed by the tetrahedral alignment in <100> and <110> directions, respectively. These nanoballs were characterized by HRSEM/TEM/STEM/EELS and Raman to confirm the phase purity and bonding characteristics. The Q-carbon balls exhibit robust ferromagnetism and field emission in pure and undoped form and show highest BCS superconducting transition temperature upon doping with boron. The ferromagnetism in Q-carbon balls can be varied with size and achieve higher coercively than thin films, and these balls can be coated with drugs for targeted delivery. In view of these properties, nanoballs are expected to find novel applications ranging from targeted delivery to nanosensing and superconducting qubits.}, journal={CARBON}, author={Narayan, J. and Khosla, N.}, year={2022}, month={Jun}, pages={301–307} }
 @article{moatti_mineo-foley_gupta_sachan_narayan_2022, title={Spin Engineering of VO2 Phase Transitions and Removal of Structural Transition}, volume={14}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.1c24978}, DOI={10.1021/acsami.1c24978}, abstractNote={Vanadium dioxide undergoes a metal-to-insulator transition, where the energy of electron-electron, electron-lattice, spin-spin, and spin-lattice interactions are of the same order of magnitude. This leads to the coexistence of electronic and structural transitions in VO2 that limit the lifetime and speed of VO2-based devices. However, the closeness of interaction energy of lattice-electron-spin can be turned into an opportunity to induce some transitions while pinning others via external stimuli. That is, the contribution of spin, charge, orbital, and lattice degrees of freedom can be manipulated. In this study, spin engineering has been exploited to affect the spin-related interactions in VO2 by introducing a ferromagnetic Ni layer. The coercivity in the Ni layer is engineered by controlling the shape anisotropy via kinetics of growth. Using spin engineering, the structural pinning of the monoclinic M2 phase of VO2 is successfully achieved, while the electronic and magnetic transitions take place.}, number={10}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Moatti, Adele and Mineo-Foley, Gabrielle and Gupta, Siddharth and Sachan, Ritesh and Narayan, Jay}, year={2022}, month={Mar}, pages={12883–12892} }
 @misc{joshi_riley_gupta_narayan_narayan_2021, title={Advances in laser-assisted conversion of polymeric and graphitic carbon into nanodiamond films}, volume={32}, ISSN={["1361-6528"]}, url={https://doi.org/10.1088/1361-6528/ac1097}, DOI={10.1088/1361-6528/ac1097}, abstractNote={Nanodiamond (ND) synthesis by nanosecond laser irradiation has sparked tremendous scientific and technological interest. This review describes efforts to obtain cost-effective ND synthesis from polymers and carbon nanotubes (CNT) by the melting route. For polymers, ultraviolet (UV) irradiation triggers intricate photothermal and photochemical processes that result in photochemical degradation, subsequently generating an amorphous carbon film; this process is followed by melting and undercooling of the carbon film at rates exceeding 109 K s−1. Multiple laser shots increase the absorption coefficient of PTFE, resulting in the growth of 〈110〉 oriented ND film. Multiple laser shots on CNTs result in pseudo topotactic diamond growth to form a diamond fiber. This technique is useful for fabricating 4–50 nm sized NDs. These NDs can further be employed as seed materials that are used in bulk epitaxial growth of microdiamonds using chemical vapor deposition, particularly for use with non-lattice matched substrates that formerly did not form continuous and adherent films. We also provide insights into biocompatible precursors for ND synthesis such as polybenzimidazole fiber. ND fabrication by UV irradiation of graphitic and polymeric carbon opens up a pathway for preparing selective coatings of polymer-diamond composites, doped nanodiamonds, and graphene composites for quantum computing and biomedical applications.}, number={43}, journal={NANOTECHNOLOGY}, publisher={IOP Publishing}, author={Joshi, Pratik and Riley, Parand and Gupta, Siddharth and Narayan, Roger J. and Narayan, Jagdish}, year={2021}, month={Oct} }
 @article{mandal_gupta_beavers_singh_narayan_sachan_2021, title={Atomic-Scale Insights on Large-Misfit Heterointerfaces in LSMO/MgO/c-Al2O3}, volume={11}, ISSN={["2073-4352"]}, DOI={10.3390/cryst11121493}, abstractNote={Understanding the interfaces in heterostructures at an atomic scale is crucial in enabling the possibility to manipulate underlying functional properties in correlated materials. This work presents a detailed study on the atomic structures of heterogeneous interfaces in La0.7Sr0.3MnO3 (LSMO) film grown epitaxially on c-Al2O3 (0001) with a buffer layer of MgO. Using aberration-corrected scanning transmission electron microscopy, we detected nucleation of periodic misfit dislocations at the interfaces of the large misfit systems of LSMO/MgO and MgO/c-Al2O3 following the domain matching epitaxy paradigm. It was experimentally observed that the dislocations terminate with 4/5 lattice planes at the LSMO/MgO interface and with 12/13 lattice planes at the MgO/c-Al2O3 interface. This is consistent with theoretical predictions. Using the atomic-resolution image data analysis approach to generate atomic bond length maps, we investigated the atomic displacement in the LSMO/MgO and MgO/c-Al2O3 systems. Minimal presence of residual strain was shown at the respective interface due to strain relaxation following misfit dislocation formation. Further, based on electron energy-loss spectroscopy analysis, we confirmed an interfacial interdiffusion within two monolayers at both LSMO/MgO and MgO/c-Al2O3 interfaces. In essence, misfit dislocation configurations of the LSMO/MgO/c-Al2O3 system have been thoroughly investigated to understand atomic-scale insights on atomic structure and interfacial chemistry in these large misfit systems.}, number={12}, journal={CRYSTALS}, author={Mandal, Soumya and Gupta, Ashish Kumar and Beavers, Braxton Hays and Singh, Vidit and Narayan, Jagdish and Sachan, Ritesh}, year={2021}, month={Dec} }
 @article{narayan_2021, title={Discovery of double helix of screw dislocations: a perspective}, volume={9}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2021.1973131}, abstractNote={We discuss the conversion of a pure screw dislocation into a helical (single helix) dislocation through absorption of vacancies. These helical dislocations having some edge and mostly screw character can pair up through attractive interaction to form a double helix. This attractive interaction between two helices is derived through the edge component of mixed dislocations and from the presence of vacancy jogs. Recent results on the growth of GeS [1] and PbS [3] nanowires with Eshelby twist showed large disagreements between experimental and theoretical Burgers vectors for these crystal structures, which can be resolved by introducing the double helix of screw dislocations. IMPACT STATEMENT Single helix and double helix of screw dislocations provide continuous growth steps for all crystalline structures. Thus, nanostructures materials can be grown without any need for catalysts. These dislocations also introduce Eshelby twist and create novel nanostructured materials with unique properties.}, number={11}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, J.}, year={2021}, month={Nov}, pages={453–457} }
 @misc{doping and fabrication of diamond and c-bn based device structures_2021, journal={US Patent # 11011514}, year={2021} }
 @article{riley_joshi_azizi machekposhti_sachan_narayan_narayan_2021, title={Enhanced Vapor Transmission Barrier Properties via Silicon-Incorporated Diamond-Like Carbon Coating}, volume={13}, ISSN={["2073-4360"]}, DOI={10.3390/polym13203543}, abstractNote={In this study, we describe reducing the moisture vapor transmission through a commercial polymer bag material using a silicon-incorporated diamond-like carbon (Si-DLC) coating that was deposited using plasma-enhanced chemical vapor deposition. The structure of the Si-DLC coating was analyzed using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and electron energy loss spectroscopy. Moisture vapor transmission rate (MVTR) testing was used to understand the moisture transmission barrier properties of Si-DLC-coated polymer bag material; the MVTR values decreased from 10.10 g/m2 24 h for the as-received polymer bag material to 6.31 g/m2 24 h for the Si-DLC-coated polymer bag material. Water stability tests were conducted to understand the resistance of the Si-DLC coatings toward moisture; the results confirmed the stability of Si-DLC coatings in contact with water up to 100 °C for 4 h. A peel-off adhesion test using scotch tape indicated that the good adhesion of the Si-DLC film to the substrate was preserved in contact with water up to 100 °C for 4 h.}, number={20}, journal={POLYMERS}, author={Riley, Parand R. and Joshi, Pratik and Azizi Machekposhti, Sina and Sachan, Ritesh and Narayan, Jagdish and Narayan, Roger J.}, year={2021}, month={Oct} }
 @article{riley_joshi_narayan_narayan_2021, title={Enhanced nucleation and large-scale growth of CVD diamond via surface-modification of silicon-incorporated diamond-like carbon thin films}, volume={120}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2021.108630}, abstractNote={Herein we report a method to tailor the surface of silicon-incorporated diamond-like carbon (Si-DLC) thin films to enhance the diamond nucleation density and growth. In this technique, the surfaces of Si-DLC films were modified by fluorine and oxygen species utilizing a reactive-ion etching (RIE) method. The surface properties of Si-DLC, oxygen-terminated Si-DLC (O Si-DLC), and fluorine-terminated Si-DLC (F Si-DLC) films were investigated and compared. The analyses depicted that the sp2/sp3 ratio of carbon‑carbon bonds has diminished from 20.28% for Si-DLC film down to 8.96% and 4.41% for O Si-DLC and F Si-DLC films, respectively. Moreover, a significant amount of new sp3 hybridized bonds formed on the surface of the modified Si-DLC thin films, particularly in F Si-DLC film. The deposition of micro-diamond on the films was performed using hot filament chemical vapor deposition (HFCVD). SEM, XRD, and Raman results showed the enhancement in nucleation density and growth of micro-diamond on F Si-DLC and O Si-DLC films and the in-plane stress reduction up to 60%. Owing to the lower number of sp2 bonds and the greater number of new sp3 sites, the F Si-DLC thin film provided a superior platform for diamond nucleation than O Si-DLC film. The continuous diamond coverage on F Si-DLC film was up to ~2 mm2 versus ~0.4 mm2 for O Si-DLC film.}, journal={DIAMOND AND RELATED MATERIALS}, author={Riley, Parand R. and Joshi, Pratik and Narayan, Jagdish and Narayan, Roger J.}, year={2021}, month={Dec} }
 @article{narayan_bhaumik_gupta_joshi_riley_narayan_2021, title={Formation of self-organized nano- and micro-diamond rings}, volume={9}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2021.1907627}, abstractNote={We report formation of self-organized nanodiamond ring structures due to dynamical heterogeneity in super undercooled carbon, created by nanosecond laser melting of amorphous carbon layers. We envisage that diamond tetrahedra self-organize and lead to formation of string and ring structures on which nanodiamonds nucleate and grow. Denser ring structures are formed in Q-carbon due to higher undercooling and enhanced diamond nucleation. The average size is larger under heterogeneous nucleation compared to homogeneous nucleation due to lower critical size and free energy, allowing more time for growth. With nanosecond laser melting, growth velocities range 5–10 ms−1 and even higher for Q-carbon. GRAPHICAL ABSTRACT IMPACT STATEMENT Significant advancement in the creation of self-organized nanodiamond ring and string structures by laser processing at ambient pressure and temperature}, number={7}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, J. and Bhaumik, A. and Gupta, S. and Joshi, P. and Riley, P. and Narayan, R. J.}, year={2021}, month={Mar}, pages={300–307} }
 @article{joshi_gupta_riley_narayan_narayan_2021, title={Liquid phase regrowth of (110) nanodiamond film by UV laser annealing of PTFE to generate dense CVD microdiamond film}, volume={117}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2021.108481}, abstractNote={Herein we report the conversion of polytetrafluoroethylene (PTFE) into 〈110〉 nanodiamonds via a melting route using pulsed laser annealing (PLA). The converted nanodiamond (ND) film is used as a seed layer to grow dense microdiamond coating synthesized by chemical vapor deposition. We utilize an ArF excimer laser with a photon energy of 6.4 eV to decompose PTFE (bandgap: 6.0 eV). Initial laser pulses result in photochemical decomposition of PTFE, and PTFE is converted to an amorphous carbon film. This amorphous carbon film, when subjected to additional laser pulses melts, and when this melt is quenched from an undercooled state at rates exceeding 109 K/s, it undergoes first-order phase transformation into the ND film. Notably, the obtained NDs are phase pure, exhibiting full width at half maxima (FWHM) of 1.23 cm−1 and demonstrating 〈110〉 out of plane orientation characterized by Raman spectroscopy and transmission electron microscopy, respectively. The average ND size is ~28.5 nm (range: 5-30 nm) determined by scanning electron microscopy and X-ray diffraction. The COMSOL simulations substantiate the use of nanosecond laser pulses with an energy density in the range of 0.6–0.8 J/cm2 to fully convert ~ 50% crystalline PTFE into ND film. The CVD microdiamonds grew densely on the ND seed layer as compared to reduced graphene oxide confirmed by SEM and Raman analysis. This innovative method of ND fabrication by UV irradiation of PTFE opens up opportunities for generating selective coatings of advanced polymer-diamond composites and doped nanodiamonds for quantum computing and biomedical applications.}, journal={DIAMOND AND RELATED MATERIALS}, author={Joshi, Pratik and Gupta, Siddharth and Riley, Parand R. and Narayan, Roger J. and Narayan, Jagdish}, year={2021}, month={Aug} }
 @article{riley_joshi_penchev_narayan_narayan_2021, title={One-Step Formation of Reduced Graphene Oxide from Insulating Polymers Induced by Laser Writing Method}, volume={11}, ISSN={["2073-4352"]}, DOI={10.3390/cryst11111308}, abstractNote={Finding a low-cost and effective method at low temperatures for producing reduced graphene oxide (rGO) has been the focus of many efforts in the research community for almost two decades. Overall, rGO is a promising candidate for use in supercapacitors, batteries, biosensors, photovoltaic devices, corrosion inhibitors, and optical devices. Herein, we report the formation of rGO from two electrically insulating polymers, polytetrafluoroethylene (PTFE) and meta-polybenzimidazole fiber (m-PBI), using an excimer pulsed laser annealing (PLA) method. The results from X-ray diffraction, scanning electron microscopy, electron backscattered diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy confirm the successful generation of rGO with the formation of a multilayered structure. We investigated the mechanisms for the transformation of PTFE and PBI into rGO. The PTFE transition occurs by both a photochemical mechanism and a photothermal mechanism. The transition of PBI is dominated by a photo-oxidation mechanism and stepwise thermal degradation. After degradation and degassing procedures, both the polymers leave behind free molten carbon with some oxygen and hydrogen content. The free molten carbon undergoes an undercooling process with a regrowth velocity (<4 m·s−1) that is necessary for the formation of rGO structures. This approach has the potential for use in creating future selective polymer-written electronics.}, number={11}, journal={CRYSTALS}, author={Riley, Parand R. and Joshi, Pratik and Penchev, Hristo and Narayan, Jagdish and Narayan, Roger J.}, year={2021}, month={Nov} }
 @article{narayan_joshi_smith_gao_weber_narayan_2022, title={Q-carbon as a new radiation-resistant material}, volume={186}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2021.10.006}, abstractNote={We have discovered that Q-carbon is extremely resistant to radiation damage under ion irradiations involving extreme atomic displacements and electronic excitations. Using 5 MeV Au + ions, the Q-carbon films on sapphire substrates were irradiated in the dose range 3.3–10 dpa (displacements-per-atom). After the ion irradiations, detailed studies on the atomic structure and bonding characteristics showed that atomic structure and bonding characteristics of amorphous Q-carbon remained essentially unchanged to 10 dpa of radiation damage, which is equivalent to over twenty years of neutron damage in a conventional reactor. There was an ion-beam mixed layer below the Q-carbon layer, whose thickness increased from 5 nm to 10 nm, as the dose increased from 3.3 to 10 dpa. This layer was found to be mostly amorphous with a mixture Al2O3 and Al4C3. This layer, formed as a result of enhanced forward scattering and ballistic ion beam mixing, exhibited composition consistent with detailed TRIM calculations. We also found that nanodiamonds (3 nm average size) embedded in Q-carbon grew to about 60 nm after 6.6 dpa and shrank to about 40 nm after 10 dpa. We discuss the mechanism for the growth and shrinkage of metastable phase of diamond under nonequilibrium ion irradiations.}, journal={CARBON}, author={Narayan, J. and Joshi, P. and Smith, J. and Gao, W. and Weber, W. J. and Narayan, R. J.}, year={2022}, month={Jan}, pages={253–261} }
 @article{narayan_bhaumik_gupta_joshi_riley_narayan_2021, title={Role of Q-carbon in nucleation and formation of continuous diamond film}, volume={176}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2021.02.049}, abstractNote={Formation of continuous and adherent diamond films on practical substrates presents a formidable challenge due to lack of diamond nucleation sites needed for diamond growth. This problem has been solved through the formation of interfacial Q-carbon layers by nanosecond laser melting of carbon layers in a highly undercooled state and subsequent quenching. The Q-carbon layer provides ready nucleation sites for epitaxial films on planar matching substrates such as sapphire, and polycrystalline films on amorphous substrates such as glass. Each laser pulse converts about a one-cm-square area, which can be repeated with a 100–200 Hz laser to produce potentially 100–200 cm2s-1 of diamond films. This is essentially a low-temperature processing, where substrate stays close to ambient temperature, because the total heat input is quite small. The Q-carbon layer is also responsible for improved adhesion of diamond films on sapphire and glass substrates. It is also argued that the formation of Q-carbon layer is also responsible for efficient diamond nucleation during negatively biased MPCVD diamond depositions.}, journal={CARBON}, author={Narayan, J. and Bhaumik, A. and Gupta, S. and Joshi, P. and Riley, P. and Narayan, R. J.}, year={2021}, month={May}, pages={558–568} }
 @article{huang_wang_li_jin_lu_zhang_lin_chen_narayan_zhang_et al._2020, title={3D Hybrid Plasmonic Framework with Au Nanopillars Embedded in Nitride Multilayers Integrated on Si}, volume={7}, ISSN={["2196-7350"]}, DOI={10.1002/admi.202000493}, abstractNote={AbstractIntegration of nanoscale photonic and plasmonic components on Si substrates is a critical step toward Si‐based integrated nanophotonic devices. In this work, a set of unique complex 3D metamaterials with intercalated nanolayered and nanopillar structures with tunable plasmonic and optical properties on Si substrates is designed. More specifically, the 3D metamaterials combine metal (Au) nanopillars and alternating metal‐nitride (Au‐TiN and Au‐TaN) nanolayers, epitaxially grown on Si substrates. The ultrafine Au nanopillars (d ≈ 3 nm) continuously grow throughout all the nanolayers with high epitaxial quality. Novel optical properties, such as highly anisotropic optical property, high absorbance covering the entire visible spectrum regime, and hyperbolic property in the visible regime, are demonstrated. Furthermore, a waveguide based on a silicon nitride (Si3N4) ridge with a multilayer structure is successfully fabricated. The demonstration of 3D nanoscale metamaterial design integrated on Si opens up a new route toward tunable metamaterials nanostructure designs with versatile material selection for various optical components in Si integrated photonics.}, number={17}, journal={ADVANCED MATERIALS INTERFACES}, author={Huang, Jijie and Wang, Xuejing and Li, Dongfang and Jin, Tiening and Lu, Ping and Zhang, Di and Lin, Pao-Tai and Chen, Hou-Tong and Narayan, Jagdish and Zhang, Xinghang and et al.}, year={2020}, month={Sep} }
 @article{moatti_sachan_kumar_narayan_2019, title={Catalyst-assisted epitaxial growth of ferromagnetic TiO2/TiN nanowires}, volume={167}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/J.ACTAMAT.2019.01.052}, DOI={10.1016/J.ACTAMAT.2019.01.052}, abstractNote={We report a novel method of growth for single-crystalline TiO2/TiN nanowires through oxidation of epitaxial TiN nanowires on Si-SiO2 (amorphous) and c-sapphire (crystalline) as practical substrates. We propose that the laser ablated Ti and N diffuse into molten Au to form TiN nanodots where the growth rate of nanowires is directly proportional to the laser ablation flux due to high diffusion in molten Au. The TiN nanowires were grown by Pulsed Laser Deposition method using Au as a catalyst. The TiN nanowires were then oxidized to create TiO2/TiN core-shell nanowires. The growth of TiO2 (rutile) occurs by domain matching epitaxy paradigm in such a way that (002) planes of the TiO2 match with (200) plane of TiN, where the TiO2 thickness can be tuned by adjustment of oxidation time and temperature. This design provides a core-shell structure of TiO2/TiN nanowires integrated with silicon and sapphire substrates. The Rutile TiO2 nanowires show ferromagnetic behavior, while the as-grown TiN exhibits diamagnetic behavior. The SEM, TEM, and EBSD are used to characterize the microstructure and atomic alignments of TiO2 nanowires. The simple method of oxidation combined with tunable magnetic properties provides benefits to many smart applications where the magnetic field can be used as an external stimulation.}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Moatti, A. and Sachan, R. and Kumar, D. and Narayan, J.}, year={2019}, month={Apr}, pages={112–120} }
 @article{narayan_bhaumik_sachan_haque_gupta_pant_2019, title={Direct conversion of carbon nanofibers and nanotubes into diamond nanofibers and the subsequent growth of large-sized diamonds}, volume={11}, ISSN={2040-3364 2040-3372}, url={http://dx.doi.org/10.1039/C8NR08823C}, DOI={10.1039/C8NR08823C}, abstractNote={We report a pulsed laser annealing method to convert carbon fibers and nanotubes into diamond fibers under ambient conditions.}, number={5}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Narayan, J. and Bhaumik, A. and Sachan, R. and Haque, A. and Gupta, S. and Pant, P.}, year={2019}, pages={2238–2248} }
 @article{bhaumik_narayan_2019, title={Direct conversion of carbon nanofibers into diamond nanofibers using nanosecond pulsed laser annealing}, volume={21}, ISSN={["1463-9084"]}, DOI={10.1039/c9cp00063a}, abstractNote={The formation of DNFs utilizing a low-temperature budget route will revolutionize their use in electronic, biomedical, and photonic devices.}, number={13}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, month={Apr}, pages={7208–7219} }
 @article{moatti_sachan_cooper_narayan_2019, title={Electrical Transition in Isostructural VO2 Thin-Film Heterostructures}, volume={9}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/S41598-019-39529-Z}, DOI={10.1038/S41598-019-39529-Z}, abstractNote={AbstractControl over the concurrent occurrence of structural (monoclinic to tetragonal) and electrical (insulator to the conductor) transitions presents a formidable challenge for VO2-based thin film devices. Speed, lifetime, and reliability of these devices can be significantly improved by utilizing solely electrical transition while eliminating structural transition. We design a novel strain-stabilized isostructural VO2 epitaxial thin-film system where the electrical transition occurs without any observable structural transition. The thin-film heterostructures with a completely relaxed NiO buffer layer have been synthesized allowing complete control over strains in VO2 films. The strain trapping in VO2 thin films occurs below a critical thickness by arresting the formation of misfit dislocations. We discover the structural pinning of the monoclinic phase in (10 ± 1 nm) epitaxial VO2 films due to bandgap changes throughout the whole temperature regime as the insulator-to-metal transition occurs. Using density functional theory, we calculate that the strain in monoclinic structure reduces the difference between long and short V-V bond-lengths (ΔV−V) in monoclinic structures which leads to a systematic decrease in the electronic bandgap of VO2. This decrease in bandgap is additionally attributed to ferromagnetic ordering in the monoclinic phase to facilitate a Mott insulator without going through the structural transition.}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Moatti, Adele and Sachan, Ritesh and Cooper, Valentino R and Narayan, Jagdish}, year={2019}, month={Feb} }
 @article{sachan_hachtel_bhaumik_moatti_prater_idrobo_narayan_2019, title={Emergence of shallow energy levels in B-doped Q-carbon: A high-temperature superconductor}, volume={174}, url={http://dx.doi.org/10.1016/j.actamat.2019.05.013}, DOI={10.1016/j.actamat.2019.05.013}, abstractNote={We report the spectroscopic demonstration of the shallow-level energy states in the recently discovered B-doped Q-carbon Bardeen-Cooper-Schrieffer (BCS) high-temperature superconductor. The Q-carbon is synthesized by ultrafast melting and quenching, allowing for high B-doping concentrations which increase the superconducting transition temperature (Tc) to 36 K (compared to 4 K for B-doped diamond). The increase in Tc is attributed to the increased density of energy states near the Fermi level in B-doped Q-carbon, which give rise to superconducting states via strong electron-phonon coupling below Tc. These shallow-level energy states, however, are challenging to map due to limited spatial and energy resolution. Here, we use ultrahigh energy resolution monochromated electron energy-loss spectroscopy (EELS), to detect and visualize the newly formed shallow-level energy states (vibrational modes) near the Fermi level (ranging 30–100 meV) of the B-doped Q-carbon. With this study, we establish the significance of high-resolution EELS in understanding the superconducting behavior of BCS superconducting C-based materials, which demonstrate a phenomenal enhancement in the presence of shallow-level energy states.}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Sachan, Ritesh and Hachtel, Jordan A. and Bhaumik, Anagh and Moatti, Adele and Prater, John and Idrobo, Juan Carlos and Narayan, Jagdish}, year={2019}, month={Aug}, pages={153–159} }
 @article{gupta_sachan_narayan_2020, title={Evidence of weak antilocalization in epitaxial TiN thin films}, volume={498}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2019.166094}, abstractNote={Defect engineering provides a tremendous opportunity to impart novel functionalities to nanomaterials. This report is focused on TiN metallic system, where the unpaired spin structure and electron-transport are controlled by injecting nitrogen vacancies (VN). The TiN films are epitaxial, with the TiN/Al2O3 epitaxial relationship given by: (1 1 1) TiN//(0 0 0 1) Al2O3 as out-of-plane, and 〈11-0〉 TiN//〈1 0 1- 0〉 Al2O3 and 〈1 1 2-〉 TiN//〈1 1 2-0〉 Al2O3 as in-plane, after 30° rotation. Epitaxy in such a large misfit system (~9.24%) is rationalized to arise via domain matching epitaxy (DME) paradigm. Following the report of room-temperature ferromagnetism [1] in TiN1−x films formed by injecting nitrogen vacancies, we provide direct experimental evidence of weak antilocalization (WAL) effects by plugging VN using nitrogen annealing of TiN films. This evidence with simultaneous loss of magnetization in nitrogen annealed TiN films is the tell-tale sign of VN acting as magnetically active defects in TiN, as their removal facilitates Berry’s phase formation and generation of time-reversal symmetry. Through detailed EELS and Raman analysis, we have explicitly shown the absence of Ti+2 polarons in TiN films on N2 annealing. The resistivity minima in TiN films are attributed to the WAL effect with persistent log T behavior under 0–7 Tesla magnetic fields. The temperature-dependent coherence length analysis also highlights the emergence of WAL under the two-dimensional localization theory. The WAL effect in TiN is similar to topological insulators, quenching on the introduction of magnetically active defects, while stable against non-magnetic defects. Our findings demonstrate the prime importance of nitrogen vacancies in tuning the magentotransport characteristics in epitaxial nitride films for optoelectronic device applications.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Gupta, Siddharth and Sachan, Ritesh and Narayan, Jagdish}, year={2020}, month={Mar} }
 @article{zkria_haque_egiza_abubakr_murasawa_yoshitake_narayan_2019, title={Laser-induced structure transition of diamond-like carbon coated on cemented carbide and formation of reduced graphene oxide}, volume={9}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2019.88}, abstractNote={We report on the structural evolution of diamond-like carbon (DLC) films by the nanosecond pulsed laser annealing process. DLC film is coated on cemented carbide (WC-Co) by cathodic arc ion plating, which is then annealed by ArF laser (193 nm, 20 ns) at different laser fluences (0.9–1.7 J/cm^2). Upon laser annealing, Raman spectra divulge higher sp ^3 fractions accompanied by a blue shift in the G -peak position, which indicates the changes of sp ^2 sites from rings to chains. At higher fluence (>1.2 J/cm^2), the film converts into reduced graphene oxide confirmed by its Raman-active vibrational modes: D, G , and 2 D .}, number={3}, journal={MRS COMMUNICATIONS}, author={Zkria, Abdelrahman and Haque, Ariful and Egiza, Mohamed and Abubakr, Eslam and Murasawa, Koki and Yoshitake, Tsuyoshi and Narayan, Jagdish}, year={2019}, month={Sep}, pages={910–915} }
 @article{bhaumik_narayan_2019, title={Nano-to-micro diamond formation by nanosecond pulsed laser annealing}, volume={126}, ISSN={["1089-7550"]}, DOI={10.1063/1.5118890}, abstractNote={Here, we report the synthesis and characterization of nano-, micro-, twinned, and lonsdaleite diamonds, which are formed after melting and quenching of amorphous carbon or Q-carbon essentially at room temperature and atmospheric pressure. These conversions depend on the degree of undercooling, which is controlled by the laser parameters and thermal conductivities of the amorphous carbon and the substrate. The laser melting and undercooling provide liquid-phase packing of atoms similar to high-pressure, which facilitate the conversion of amorphous carbon into diamond or Q-carbon without using any catalyst. By changing the nucleation and growth rates, we have synthesized a wide range of sizes (4 nm to 3 μm) of diamond crystals. The formation of twinned and lonsdaleite diamonds is controlled by the quenching rate. Therefore, we have created a “factory of diamonds” at ambient conditions by nanosecond laser annealing, which will pave the pathway to design high-speed mechanical and electrical devices.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, month={Sep} }
 @article{akouala_kumar_punugupati_reynolds_reynolds_mily_maria_narayan_hunte_2019, title={Planar Hall effect and anisotropic magnetoresistance in semiconducting and conducting oxide thin films}, volume={125}, ISSN={0947-8396 1432-0630}, url={http://dx.doi.org/10.1007/S00339-019-2592-Y}, DOI={10.1007/S00339-019-2592-Y}, number={5}, journal={Applied Physics A}, publisher={Springer Science and Business Media LLC}, author={Akouala, Christer R. and Kumar, Raj and Punugupati, Sandhyarani and Reynolds, C. Lewis and Reynolds, Judith G. and Mily, Edward J. and Maria, Jon-Paul and Narayan, Jagdish and Hunte, Frank}, year={2019}, month={Apr} }
 @article{narayan_bhaumik_hague_2019, title={Pseudo-topotactic growth of diamond nanofibers}, volume={178}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2019.08.008}, abstractNote={We report pseudo-topotactic growth of single-crystal diamond fibers by nanosecond laser melting of amorphous carbon nanofibers (CNFs) and crystalline multi-wall carbon nanotubes (MWCNTs). A rapid laser melting in a super undercooled state and subsequent quenching convert the tips of CNFs and MWCNTs into phase-pure <110> nanodiamonds along the growth directions. Subsequent laser pluses melt regions below <110> nanodiamonds that provide seeds for epitaxial growth. By repeating this process, the length of <110> nanodiamond fibers can be increased, as each pulse results in ∼50 nm nanodiamond region, depending upon the initial size of CNFs and MWCTs. This conversion process can be carried at ambient temperature and pressure in air. The epitaxial nature of <110> nanodiamond fibers has been confirmed by systematic electron-back-scatter-diffraction studies along the fiber in high-resolution scanning electron microscopy, and high-resolution TEM imaging and diffraction. The nature of C–C bonding characteristics was studied by high-resolution electron-energy-loss spectroscopy to establish the formation of diamond phase by the characteristic peak at 292 eV for sp3 bonding (σ∗), and absence of 284 eV peak for sp2 (π∗) graphitic bonding. The characteristic diamond Raman peak at 1332 cm−1 is found to downshift to 1321 cm−1 because of phonon confinement in nanodiamonds associated with nanofibers. These nanodiamond structures can be doped with both n- and p-type dopants with concentrations far higher than thermodynamic solubility limit due to solute trapping during quenching from the liquid phase. Thus, these nanodiamond structures provide ideal platform for nanosensing, computing and communication, including efficient field emitting devices.}, journal={ACTA MATERIALIA}, author={Narayan, J. and Bhaumik, A. and Hague, A.}, year={2019}, month={Oct}, pages={179–185} }
 @article{bhaumik_narayan_2019, title={Reduced Graphene Oxide-Nanostructured Silicon Photosensors with High Photoresponsivity at Room Temperature}, volume={2}, ISSN={2574-0970 2574-0970}, url={http://dx.doi.org/10.1021/ACSANM.9B00084}, DOI={10.1021/ACSANM.9B00084}, abstractNote={We have created nanostructured Si (∼3 nm) with a direct band gap of 1.37 eV on electrically conducting reduced graphene oxide (rGO) for a highly efficient photosensor. This robust photosensor is fabricated using a nonequilibrium processing route, where nanosecond excimer laser pulses melt the alternating layers of Si and amorphous carbon to form micropillars and nanoreceptors of Si on rGO layers. The incident white light generates free carriers in the Si microstructures and nanoreceptors which are ballistically transported (via rGO layers) to the external circuit under the application of a voltage bias. The responsivity of rGO-Si devices to light (resistance vs time) and I–V measurements indicate an exponential drop in resistance with the incidence of white light and nonrectifying nature, respectively. Photoresponsivity of the rGO-Si devices is calculated to be 3.55 A/W at room temperature, which is significantly larger than the previously fabricated graphene-based ohmic photosensors. Temperature-dependen...}, number={4}, journal={ACS Applied Nano Materials}, publisher={American Chemical Society (ACS)}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, month={Jan}, pages={2086–2098} }
 @article{narayan_sachan_bhaumik_2019, title={Search for near room-temperature superconductivity in B-doped Q-carbon}, volume={7}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2019.1569566}, abstractNote={ABSTRACT We present 1D, 2D and 3D structures of boron-doped Q-carbon with a higher superconducting transition temperature than the current value of 55 K in 25 at% B-doped amorphous Q-carbon. The higher transition temperature is predicted for 1D and 2D crystalline structures with increasing density of states near the Fermi level through dopant trapping in substitutional sites. We have synthesized 50at% B-doped Q-carbon where diamond tetrahedra are arranged randomly and packed with over 80% efficiency to generate an amorphous structure. Detailed EELS measurements show higher density of states near the Fermi level above 90 K and preliminary transport data show signature of Tc above 100 K. GRAPHICAL ABSTRACT IMPACT STATEMENT Novel 1D, 2D and 3D structures of boron-doped Q-carbon with higher Tc than current BCS record of 55K by increasing B-concentration and the density of states near the Fermi level.}, number={4}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, J. and Sachan, R. and Bhaumik, A.}, year={2019}, pages={164–172} }
 @article{bhaumik_narayan_2019, title={Structure–property correlations in phase-pure B-doped Q-carbon high-temperature superconductor with a record Tc = 55 K}, volume={11}, ISSN={2040-3364 2040-3372}, url={http://dx.doi.org/10.1039/C9NR00562E}, DOI={10.1039/C9NR00562E}, abstractNote={The discovery of record BCS Tc = 55 K superconductivity in phase-pure B-doped Q-carbon will provide the pathway to achieve room-temperature superconductivity.}, number={18}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, pages={9141–9154} }
 @article{haque_sachan_narayan_2019, title={Synthesis of diamond nanostructures from carbon nanotube and formation of diamond-CNT hybrid structures}, volume={150}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2019.05.027}, abstractNote={We report direct conversion of multiwall carbon nanotubes (CNTs), synthesized by chemical vapor deposition, into diamond by nanosecond pulsed laser melting process at ambient temperature and pressure in air without any catalysts. The Raman spectroscopy of the CNTs after the laser irradiation showed the characteristic diamond peak at around 1324-1325 cm−1. The downshift of this peak from its theoretical position (at 1332 cm−1) is explained by phonon confinement in nanostructured diamond. The SEM and TEM images show the formation of diamond mostly at the tip and bends of the CNTs. The grain size distribution and the shape of the converted nanodiamonds suggest that the transformation takes place by melting of the CNTs in a super undercooled state by nanosecond laser pulses, and subsequent rapid quenching to convert it into phase-pure diamond. The EBSD analysis illustrates the phase-pure single crystal diamond formation at the tips and bends of the CNTs. The high-resolution electron energy-loss spectrum in the STEM contains characteristic σ* peak at 292 eV for sp3 bonding of diamond. This study on the laser-induced direct conversion of CNTs to diamond marks a major breakthrough in the formation of diamond nanostructures and diamond-CNT hybrid for a variety of potential applications.}, journal={CARBON}, author={Haque, Ariful and Sachan, Ritesh and Narayan, Jagdish}, year={2019}, month={Sep}, pages={388–395} }
 @article{moatti_sachan_prater_narayan_2018, title={An optimized sample preparation approach for atomic resolution in situ studies of thin films}, volume={81}, ISSN={1059-910X 1097-0029}, url={http://dx.doi.org/10.1002/JEMT.23130}, DOI={10.1002/JEMT.23130}, abstractNote={AbstractThis work provides the details of a simple and reliable method with less damage to prepare electron transparent samples for in situ studies in scanning/transmission electron microscopy. In this study, we use epitaxial VO2 thin films grown on c‐Al2O3 by pulsed laser deposition, which have a monoclinic–rutile transition at ~68°C. We employ an approach combining conventional mechanical wedge‐polishing and Focused Ion beam to prepare the electron transparent samples of epitaxial VO2 thin films. The samples are first mechanically wedge‐polished and ion‐milled to be electron transparent. Subsequently, the thin region of VO2 films are separated from the rest of the polished sample using a focused ion beam and transferred to the in situ electron microscopy test stage. As a critical step, carbon nanotubes are used as connectors to the manipulator needle for a soft transfer process. This is done to avoid shattering of the brittle substrate film on the in situ sample support stage during the transfer process. We finally present the atomically resolved structural transition in VO2 films using this technique. This approach significantly increases the success rate of high‐quality sample preparation with less damage for in situ studies of thin films and reduces the cost and instrumental/user errors associated with other techniques.The present work highlights a novel, simple, reliable approach with reduced damage to make electron transparent samples for atomic‐scale insights of temperature‐dependent transitions in epitaxial thin film heterostructures using in situ TEM studies.}, number={11}, journal={Microscopy Research and Technique}, publisher={Wiley}, author={Moatti, Adele and Sachan, Ritesh and Prater, John and Narayan, Jagdish}, year={2018}, month={Oct}, pages={1250–1256} }
 @article{sachan_bhaumik_pant_prater_narayan_2019, title={Diamond film growth by HFCVD on Q-carbon seeded substrate}, volume={141}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2018.09.058}, abstractNote={While hot-filament assisted chemical vapor deposition (HFCVD) is a well-established technique to synthesize diamond thin films using microdiamond seeds, the quality of grown diamond thin films is often compromised due to the presence of contaminants, i.e. graphitic entities and the eroded tungsten filament remnants, at the film-substrate interface. Here, we present a novel approach to form high-quality, contamination-free diamond thin films with HFCVD using Q-carbon precursor. The Q-carbon is a metastable phase which is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the superundercooled state and consists of ∼75% sp3 and rest sp2 hybridized carbon. Using Q-carbon seeds in HFCVD, we demonstrate the growth of polycrystalline diamond film with a clean interface without any tungsten filament impurities. With large-area vibrational Raman mode analysis, we also observe a significant reduction in the presence of overall graphitic entities in the diamond film. With the realization of such a high-quality interface, we present a pathway to fabricate significantly improved diamond coatings and solid-state devices.}, journal={CARBON}, author={Sachan, Ritesh and Bhaumik, Anagh and Pant, Punam and Prater, John and Narayan, Jagdish}, year={2019}, month={Jan}, pages={182–189} }
 @article{bhaumik_narayan_2018, title={Electrochromic effect in Q-carbon}, volume={112}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.5023613}, DOI={10.1063/1.5023613}, abstractNote={Here, we report the electrochromic effect in undoped Q-carbon. This unique phase of carbon, Q-carbon, is formed by pulsed laser melting of amorphous carbon and subsequent ultrafast quenching process. The excess amount of unpaired electrons near the Fermi energy level in the Q-carbon causes a 48% increase in the optical absorption at 265 nm with an applied electric field of 10 V. The Kelvin probe force microscopy (KPFM) also indicates that the Fermi level of Q-carbon is situated ∼40 meV higher than that in the neighboring diamond-like carbon region. It is also observed that, with an increase in the tip voltage from 0 to 10 V in KPFM, there occurs an increase in the image phase contrast thereby indicating an increase in the concentration of electrons. This causes an increase in optical absorbance with the application of an electric field in Q-carbon. The direct and indirect optical band gaps in Q-carbon are calculated to be 3.82 and 2.93 eV, respectively, using the Tauc analysis. High-resolution scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction pattern depict the formation and amorphous nature of Q-carbon. Raman and electron energy-loss spectroscopy of Q-carbon reveal over 75% sp3-bonded carbon (rest sp2) and excess electrons near the Fermi level. This discovery of electrochromic effect in Q-carbon shows that highly non-equilibrium synthesis can be elegantly used to fabricate smart windows with immense energy-saving applications.}, number={22}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2018}, month={May}, pages={223104} }
 @article{haque_narayan_2018, title={Electron field emission from Q-carbon}, volume={86}, ISSN={["1879-0062"]}, DOI={10.1016/j.diamond.2018.04.008}, abstractNote={We report field electron emission investigations in Q-carbon composite structures formed by pulsed laser annealing of amorphous carbon layers. Under the optimum fabrication conditions, a dense microstructured morphology of Q-carbon was obtained, which is important for local electric field enhancement in field-emission device applications. The turn-on field required to draw an emission current density of 1 μA/cm2 is found to be 2.4 V/μm. The Q-carbon films show good electron emission stability as a function of time up to 4 h. The microstructure and morphology of the field emitting Q-carbon films was analyzed by a variety of techniques, including field emission scanning electron microscope, Raman spectroscopy, and atomic force microscopy. Our results show a very high emission current density value of ~30 μA/cm2 at an applied electric field of 2.65 V/μm, which is hysteresis-free and stable. The generated emission current has been found to have low fluctuations (<4%) and shows no generation of defects during repeated emission measurements on the sample. Our findings thus hold a great promise for the development of Q-carbon films in applications ranging from field emitters and frictionless motors to heterostructures for novel micro and nano-electronic devices.}, journal={DIAMOND AND RELATED MATERIALS}, author={Haque, Ariful and Narayan, Jagdish}, year={2018}, month={Jun}, pages={71–78} }
 @article{bhaumik_narayan_2019, title={Formation and characterization of nano- and microstructures of twinned cubic boron nitride}, volume={21}, ISSN={1463-9076 1463-9084}, url={http://dx.doi.org/10.1039/C8CP04592E}, DOI={10.1039/C8CP04592E}, abstractNote={The controlled growth of phase-pure nano- and microstructures of twinned c-BN will have tremendous impact on electrical and mechanical devices.}, number={4}, journal={Physical Chemistry Chemical Physics}, publisher={Royal Society of Chemistry (RSC)}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2019}, pages={1700–1710} }
 @article{narayan_bhaumik_sachan_2018, title={High temperature superconductivity in distinct phases of amorphous B-doped           Q-carbon}, volume={123}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.5016397}, DOI={10.1063/1.5016397}, abstractNote={Distinct phases of B-doped Q-carbon are formed when B-doped and undoped diamond tetrahedra are packed randomly after nanosecond laser melting and quenching of carbon. By changing the ratio of doped to undoped tetrahedra, distinct phases of B-doped Q-carbon with concentration varying from 5.0% to 50.0% can be created. We have synthesized three distinct phases of amorphous B-doped Q-carbon, which exhibit high-temperature superconductivity following the Bardeen-Cooper-Schrieffer mechanism. The first phase (QB1) has a B-concentration ∼17 at. % (Tc = 37 K), the second phase (QB2) has a B-concentration ∼27 at. % (Tc = 55 K), and the third phase (QB3) has a B-concentration ∼45 at. % (Tc expected over 100 K). From geometrical modeling, we derive that QB1 consists of randomly packed tetrahedra, where one out of every three tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 16.6 at. %. QB2 consists of randomly packed tetrahedra, where one out of every two tetrahedra contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 25 at. %. QB3 consists of randomly packed tetrahedra, where every tetrahedron contains a B atom in the center which is sp3 bonded to four carbon atoms with a concentration of 50 at. %. We present detailed high-resolution TEM results on structural characterization, and EELS and Raman spectroscopy results on the bonding characteristics of B and C atoms. From these studies, we conclude that the high electronic density of states near the Fermi energy level coupled with moderate electron-phonon coupling result in high-temperature superconductivity in B-doped Q-carbon.}, number={13}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, Jagdish and Bhaumik, Anagh and Sachan, Ritesh}, year={2018}, month={Apr}, pages={135304} }
 @article{jaipan_nannuri_mucha_singh_xu_moatti_narayan_fialkova_kotoka_yarmolenko_et al._2018, title={Influence of Gold Catalyst on the Growth o Titanium Nitride Nanowires}, volume={7}, ISSN={["2169-4303"]}, DOI={10.1166/mat.2018.1571}, number={5}, journal={MATERIALS FOCUS}, author={Jaipan, Panupong and Nannuri, Chandra and Mucha, Nikhil Reddy and Singh, Mayur P. and Xu, Zhigang and Moatti, Adele and Narayan, Jay and Fialkova, Svitlana and Kotoka, Ruben and Yarmolenko, Sergey and et al.}, year={2018}, month={Oct}, pages={720–725} }
 @article{haque_pant_narayan_2018, title={Large-area diamond thin film on Q-carbon coated crystalline sapphire by HFCVD}, volume={504}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2018.09.036}, abstractNote={The growth of diamond on transparent substrates like sapphire presents a great challenge because of the large thermal misfit between the film and the substrate, absence of any carbide layer during diamond growth, and low nucleation density during chemical vapor deposition (CVD) growth process. In this study, we report on the use and the role of Q-carbon as an intermediate layer to successfully deposit large-area diamond film on c-sapphire by hot filament chemical vapor deposition (HFCVD). The Q-carbon consists of very high-density diamond tetrahedra which act as the embryo for diamond nucleation. Different techniques such as X-ray diffraction, scanning electron microscopy, and Raman spectroscopy show that continuous diamond films with good crystallinity and without any impurity phase can be deposited on the Q-carbon coated single crystal sapphire substrate. The Q-carbon layer is very adherent and it negates the thermal mismatch between the diamond film and the sapphire substrate. A small blue shift in the Raman peak of the diamond from its equilibrium position suggests the deposition of the CVD diamond film with minimal stress (1.14 GPa). This technique of growing large-area continuous diamond thin film with excellent crystalline quality on a single crystal sapphire substrate can serve as a platform for the development of next-generation corrosion and erosion resistant infrared windows, state-of-the-art optoelectronic devices, and advanced scanning probe microscopy systems.}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Haque, Ariful and Pant, Punam and Narayan, Jagdish}, year={2018}, month={Dec}, pages={17–25} }
 @article{bhaumik_sachan_narayan_2018, title={Magnetic relaxation and three-dimensional critical fluctuations in B-doped Q-carbon - a high-temperature superconductor}, volume={10}, ISSN={["2040-3372"]}, DOI={10.1039/c8nr03406k}, abstractNote={Three-dimensional critical fluctuations and Anderson–Kim logarithmic magnetic relaxations in B-doped Q-carbon high-temperature superconductor will lead to multifunctional high-speed electronic devices.}, number={26}, journal={NANOSCALE}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2018}, month={Jul}, pages={12665–12673} }
 @article{rasic_sachan_temizer_prater_narayan_2018, title={Oxygen Effect on the Properties of Epitaxial (110) La0.7Sr0.3MnO3 by Defect Engineering}, volume={10}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.8b05929}, abstractNote={The multiferroic properties of mixed valence perovskites such as lanthanum strontium manganese oxide (La0.7Sr0.3MnO3) (LSMO) demonstrate a unique dependence on oxygen concentration, thickness, strain, and orientation. To better understand the role of each variable, a systematic study has been performed. In this study, epitaxial growth of LSMO (110) thin films with thicknesses ∼15 nm are reported on epitaxial magnesium oxide (111) buffered Al2O3 (0001) substrates. Four LSMO films with changing oxygen concentration have been investigated. The oxygen content in the films was controlled by varying the oxygen partial pressure from 1 × 10-4 to 1 × 10-1 Torr during deposition and subsequent cooldown. X-ray diffraction established the out-of-plane and in-plane plane matching to be (111)MgO ∥ (0001)Al2O3 and ⟨11̅0⟩MgO ∥ ⟨101̅0⟩Al2O3 for the buffer layer with the substrate, and an out-of-plane lattice matching of (110)LSMO ∥ (111)MgO for the LSMO layer. For the case of the LSMO growth on MgO, a novel growth mode has been demonstrated, showing that three in-plane matching variants are present: (i) ⟨11̅0⟩LSMO ∥ ⟨11̅0⟩MgO, (ii) ⟨11̅0⟩LSMO ∥ ⟨101̅⟩MgO, and (iii) ⟨11̅0⟩LSMO ∥ ⟨01̅1⟩MgO. The atomic resolution scanning transmission electron microscopy (STEM) images were taken of the interfaces that showed a thin, ∼2 monolayer intermixed phase while high-angle annular dark field (HAADF) cross-section images revealed 4/5 plane matching between the film and the buffer and similar domain sizes between different samples. Magnetic properties were measured for all films and the gradual decrease in saturation magnetization is reported with decreasing oxygen partial pressure during growth. A systematic increase in the interplanar spacing was observed by X-ray diffraction of the films with lower oxygen concentration, indicating the decrease in the lattice constant in the plane due to the point defects. Samples demonstrated an insulating behavior for samples grown under low oxygen partial pressure and semiconducting behavior for the highest oxygen partial pressures. Magnetotransport measurements showed ∼36.2% decrease in electrical resistivity with an applied magnetic field of 10 T at 50 K and ∼1.3% at room temperature for the highly oxygenated sample.}, number={24}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Rasic, Daniel and Sachan, Ritesh and Temizer, Namik K. and Prater, John and Narayan, Jagdish}, year={2018}, month={Jun}, pages={21001–21008} }
 @article{singamaneni_prater_glavic_lauter_narayan_2018, title={Polarized neutron reflectivity studies on epitaxial BiFeO3/La0.7Sr0.3MnO3 heterostructure integrated with Si (100)}, volume={8}, ISSN={2158-3226}, url={http://dx.doi.org/10.1063/1.5006473}, DOI={10.1063/1.5006473}, abstractNote={This work reports polarized neutron reflectivity (PNR) measurements performed using the Magnetism Reflectometer at Oak Ridge National Laboratory on epitaxial BiFeO3(BFO)/La0.7Sr0.3MnO3(LSMO)/SrTiO3(STO)/MgO/TiN heterostructure deposited on Si (100) substrates. By measuring the angular dependence of neutrons reflected from the sample, PNR can provide insights on interface magnetic spin structure, chemical composition and magnetic depth profiles with a nanometer resolution. Our first analysis of nuclear scattering length density (NSLD) and magnetic scattering length density (MSLD) depth profiles measured at 4 K have successfully reproduced most of the expected features of this heterostructure, such as the NSLD for the Si, TiN, MgO, STO, LSMO layers and remanent magnetization (2.28μB/Mn) of bulk LSMO. However, the SLD of the BFO is decreased by about 30% from the expected value. When 5 V was applied across the BFO/LSMO interface, we found that the magnetic moment of the LSMO layer could be varied by about 15-20% at 6 K. Several mechanisms such as redistribution of oxygen vacancies, interface strain, charge screening and valence state change at the interface could be at play. Work is in progress to gain an improved in-depth understanding of these effects using MOKE and STEM-Z interface specific measurements.}, number={5}, journal={AIP Advances}, publisher={AIP Publishing}, author={Singamaneni, S. R. and Prater, J. T. and Glavic, A. and Lauter, V. and Narayan, J.}, year={2018}, month={May}, pages={055821} }
 @article{narayan_bhaumik_gupta_haque_sachan_2018, title={Progress in Q-carbon and related materials with extraordinary properties}, volume={6}, ISSN={["2166-3831"]}, url={https://doi.org/10.1080/21663831.2018.1458753}, DOI={10.1080/21663831.2018.1458753}, abstractNote={ABSTRACT This paper summarizes our research related to Q-carbon and Q-BN and direct conversion of carbon into diamond and h-BN into c-BN. Synthesis and processing of these materials are accomplished by nanosecond laser melting and subsequent quenching of amorphous carbon and nanocrystalline h-BN. Depending upon the degree of undercooling, molten carbon (or h-BN) can be converted into Q-carbon (or Q-BN) or diamond (or c-BN). The primary focus here is on the outstanding properties of these materials, including hardness greater than diamond, ferromagnetism, p- and n-type doping, NV nanodiamonds, high-temperature superconductivity in B-doped Q-carbon, enhanced field emission, superhard composite coatings, and future applications. IMPACT STATEMENT This research represents a fundamental breakthrough in the direct conversion of carbon into diamond at ambient temperatures and pressures in the air and their extraordinary properties. GRAPHICAL ABSTRACT}, number={7}, journal={MATERIALS RESEARCH LETTERS}, publisher={Taylor & Francis}, author={Narayan, Jagdish and Bhaumik, Anagh and Gupta, Siddharth and Haque, Ariful and Sachan, Ritesh}, year={2018}, pages={353–364} }
 @article{narayan_gupta_bhaumik_sachan_cellini_riedo_2018, title={Q-carbon harder than diamond}, volume={8}, ISSN={["2159-6867"]}, url={https://doi.org/10.1557/mrc.2018.35}, DOI={10.1557/mrc.2018.35}, abstractNote={A new phase of carbon named Q-carbon is found to be over 40% harder than diamond. This phase is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the super-undercooled state. Closely packed atoms in molten metallic carbon are quenched into Q-carbon with 80-85% sp ^3 and the rest sp ^2. The number density of atoms in Q-carbon can vary from 40% to 60% higher than diamond cubic lattice, as the tetrahedra packing efficiency increases from 70% to 80%. Using this semiempirical approach, the corresponding increase in Q-carbon hardness is estimated to vary from 48% to 70% compared to diamond.}, number={2}, journal={MRS COMMUNICATIONS}, publisher={Cambridge University Press (CUP)}, author={Narayan, Jagdish and Gupta, Siddharth and Bhaumik, Anagh and Sachan, Ritesh and Cellini, Filippo and Riedo, Elisa}, year={2018}, month={Jun}, pages={428–436} }
 @article{bhaumik_sachan_gupta_narayan_nori_kumar_majumdar_2018, title={Room-Temperature Ferromagnetism and Extraordinary Hall Effect in Nanostructured Q‐Carbon: Implications for Potential Spintronic Devices}, volume={1}, url={https://doi.org/10.1021/acsanm.7b00253}, DOI={10.1021/acsanm.7b00253}, abstractNote={We report extraordinary Hall effect and room-temperature ferromagnetism in undoped Q-carbon, which is formed by nanosecond pulsed laser melting and subsequent quenching process. Through detailed structure–property correlations in Q-carbon thin films, we show the excess amount of unpaired electrons near the Fermi energy level give rise to interesting magnetic and electrical properties. The analysis of the extraordinary Hall effect in Q-carbon follows nonclassical “side-jump” electronic scattering mechanism. The isothermal field-dependent magnetization plots confirm room-temperature ferromagnetism in Q-carbon with a finite coercivity at 300 K and a Curie temperature of 570 K, obtained by the extrapolation of the fits to experimental data using modified Bloch’s law. High-resolution scanning electron microscopy and transmission electron microscopy clearly illustrate the formation of Q-carbon and its subsequent conversion to single-crystalline diamond. Further, we found n-type conductivity in Q-carbon in the e...}, number={2}, journal={ACS Applied Nano Materials}, author={Bhaumik, Anagh and Sachan, Ritesh and Gupta, Siddharth and Narayan, Jagdish and Nori, Sudhakar and Kumar, Dhananjay and Majumdar, Alak Kumar}, year={2018}, month={Jun}, pages={807–819} }
 @article{gupta_moatti_bhaumik_sachan_narayan_2019, title={Room-temperature ferromagnetism in epitaxial titanium nitride thin films}, volume={166}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/J.ACTAMAT.2018.12.041}, DOI={10.1016/J.ACTAMAT.2018.12.041}, abstractNote={Localized charge injection by formation of vacancies provides an attractive platform for the development of multifunctional nanomaterials with direct implications in spintronics. However, further progress in spintronics critically depends on a deeper understanding of polaronic interactions between the localized charge states. This report is focused on TiN metallic system, which exhibits Pauli paramagnetism due to the absence of unpaired localized spin states. Here, nitrogen vacancies (VN) are used as a variable to tune the magnetic properties of epitaxial TiN thin films by thermal annealing in high-vacuum and N2 environment. Systematic introduction of VN generates robust magnetic ordering in vacuum-annealed TiN1-x films, with Curie temperature (TC) ∼700 K, and saturation magnetization (Ms) at absolute zero of 13.6 emu g−1. The signature spin-glass behavior below the irreversibility temperature (Tir ∼40 K) indicates the Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling interactions between the unpaired localized spin-states. Through spatially resolved electron energy-loss spectroscopy, we have determined the generation of unpaired localized spins at Ti+2 polarons with ∼12 ± 2 at.% VN in TiN1-x films. Such a large concentration of VN results in increased spin stiffness and high TC. These findings open a definitive pathway for tuning the magnetic nature of metallic materials for spintronic applications.}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Gupta, Siddharth and Moatti, Adele and Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2019}, month={Mar}, pages={221–230} }
 @article{gupta_bhaumik_sachan_narayan_2018, title={Structural Evolution of Q-Carbon and Nanodiamonds}, volume={70}, ISSN={1047-4838 1543-1851}, url={http://dx.doi.org/10.1007/S11837-017-2714-Y}, DOI={10.1007/S11837-017-2714-Y}, number={4}, journal={JOM}, publisher={Springer Science and Business Media LLC}, author={Gupta, Siddharth and Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2018}, month={Jan}, pages={450–455} }
 @article{rasic_sachan_prater_narayan_2019, title={Structure-property correlations in thermally processed epitaxial LSMO films}, volume={163}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2018.10.023}, abstractNote={Mixed-valence perovskites have drawn significant research interest in the past due to their exotic properties. Lanthanum Strontium Manganese Oxide (LSMO) shows a ferromagnetic ordering that can be tuned with the control of defects and strain. Here, experiments were performed to decouple the effects of strain and oxygen content, which together control the magnetic properties of the LSMO (La0.7Sr0.3MnO3). In this work, thermal treatments show promise in effectively controlling the ferromagnetic response of LSMO films. A set of three samples were grown on the same substrate-buffer (Al2O3/MgO) platform with different oxygen partial pressures and annealed above their deposition temperature (∼900 °C) in air. The physical and structural properties were measured and showed overall decrease in magnetization saturation as well as decrease in out-of-plane lattice spacing with decreasing oxygen partial pressure. A second anneal at lower (∼700 °C) temperature with flow of pure oxygen was performed for six hours to allow for defect annihilation and grain growth. All three films remained epitaxial allowing for direct correlation of magnetic measurements with defect concentration. Partial recovery of the magnetic properties and a slight increase in interplanar spacing was observed. The inability of the films to fully recover their original magnetic properties suggests irreversible strain relaxation during the initial, high-temperature air anneal. This hypothesis was further supported by the in-situ XRD that showed a linear increase in the interplanar spacing with temperature until ∼520 °C for LSMO and ∼690 °C for MgO. With further increase in temperature, the films experienced both loss of oxygen and irreversible defect nucleation and recombination. High resolution high-angle annular dark field (HAADF) images showed uniform thickness and no interfacial mixing with subsequent annealing treatments while electron energy loss spectroscopy (EELS) showed a loss of characteristic pre-peak A in oxygen indicating formation of oxygen vacancies. Parallel annealing experiments in high vacuum instead of atmosphere were performed, which showed complete loss of crystal structure in the LSMO films due to significant loss of oxygen in the lattice that irreversibly collapsed the perovskite structure. Furthermore, a low-temperature (∼500 °C) oxidation anneal was performed on a pristine sample with no change in the interplanar spacing observed indicating no change in the strain state of the film due to annealing below the deposition temperature. The reversibility of magnetic properties, which is observed as long as the crystal structure of the films is preserved, indicates the importance of bridging oxygen in controlling the magnetic behavior of mixed valence perovskites. Finally, it was determined that the highest magnetization saturation in the films is achieved with a high oxygen partial pressure during growth and subsequent thermal annealing below the deposition temperature.}, journal={ACTA MATERIALIA}, author={Rasic, Daniel and Sachan, Ritesh and Prater, John and Narayan, Jagdish}, year={2019}, month={Jan}, pages={189–198} }
 @article{bhaumik_narayan_2018, title={Synthesis and Characterization of Quenched and Crystalline Phases: Q-Carbon, Q-BN, Diamond and Phase-Pure c-BN}, volume={70}, ISSN={1047-4838 1543-1851}, url={http://dx.doi.org/10.1007/S11837-017-2712-0}, DOI={10.1007/S11837-017-2712-0}, number={4}, journal={JOM}, publisher={Springer Science and Business Media LLC}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2018}, month={Jan}, pages={456–463} }
 @article{bhaumik_sachan_narayan_2019, title={Tunable charge states of nitrogen-vacancy centers in diamond for ultrafast quantum devices}, volume={142}, ISSN={0008-6223}, url={http://dx.doi.org/10.1016/J.CARBON.2018.10.084}, DOI={10.1016/J.CARBON.2018.10.084}, abstractNote={A prerequisite condition for next-generation quantum sensing, communication, and computing is the precise modulation of the charge states of nitrogen-vacancy (NV) centers in diamond. We have achieved tuning of these centers in highly concentrated NV-diamonds using photons, phonons, and electrons. These NV-diamonds are synthesized employing a unique nanosecond laser processing technique which results in ultrafast melting and subsequent quenching of nitrogen-doped molten carbon films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can exceed thermodynamic solubility limits through solute trapping. This ultrafast synthesis technique generates fewer surface traps thereby forming ∼75% NV− centers at room-temperature, which are optically and magnetically distinct as compared to NV0 centers. We dramatically increase the NV− concentration in NV-diamonds by ∼53% with decreasing temperature from 300 to 80 K. With negative electrical biasing, the Fermi level in NV-diamond rises and crosses the NV0/- level, thereby promoting an exponential conversion of NV0 to NV− centers. We have also photonically enhanced the photoluminescence signal from NV− centers, thereby ascertaining the conversion of NV0 into NV− via absorption of electrons (excited by 532 nm photons) from the valence band in NV-diamond. These NV-centers in diamonds also reveal large excitation lifetime, which ultimately leads to ∼65% quantum efficiency at room-temperature. With these results, we believe that the precise tuning of charge states in these uniquely prepared highly concentrated NV-diamonds will lead to superior quantum devices.}, journal={Carbon}, publisher={Elsevier BV}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2019}, month={Feb}, pages={662–672} }
 @article{gupta_sachan_bhaumik_pant_narayan_2018, title={Undercooling driven growth of Q-carbon, diamond, and graphite}, volume={8}, ISSN={["2159-6867"]}, url={https://doi.org/10.1557/mrc.2018.76}, DOI={10.1557/mrc.2018.76}, abstractNote={We provide insights pertaining the dependence of undercooling in the formation of graphite, nanodiamonds, and Q-carbon nanocomposites by nanosecond laser melting of diamond-like carbon (DLC). The DLC films are melted rapidly in a super-undercooled state and subsequently quenched to room temperature. Substrates exhibiting different thermal properties-silicon and sapphire, are used to demonstrate that substrates with lower thermal conductivity trap heat flow, inducing larger undercooling, both experimentally and theoretically via finite element simulations. The increased undercooling facilitates the formation of Q-carbon. The Q-carbon is used as nucleation seeds for diamond growth via laser remelting and hot-filament chemical vapor deposition.}, number={2}, journal={MRS COMMUNICATIONS}, publisher={Cambridge University Press (CUP)}, author={Gupta, Siddharth and Sachan, Ritesh and Bhaumik, Anagh and Pant, Punam and Narayan, Jagdish}, year={2018}, month={Jun}, pages={533–540} }
 @article{moatti_sachan_gupta_narayan_2018, title={Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO2 Thin Films}, volume={11}, ISSN={1944-8244 1944-8252}, url={http://dx.doi.org/10.1021/ACSAMI.8B17879}, DOI={10.1021/ACSAMI.8B17879}, abstractNote={Vanadium dioxide (VO2) is a strongly correlated material with 3d electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron correlations. These ultrathin (∼10 nm) epitaxial VO2 films were grown on NiO(111)/Al2O3(0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain-matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies ( x ∼ 0.20 ± 0.02) into the VO2- x system via annealing under high vacuum (∼5 × 10-7 Torr) and increased temperature (450 °C). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near the Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V-V vibrational modes and stabilization of V-V dimers are observed in vacuum-annealed VO2 films, providing conclusive evidence for stabilization of a monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2- x thin films, resulting in metallic characteristics at room temperature. With these results, we propose a defect engineering pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2.}, number={3}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Moatti, Adele and Sachan, Ritesh and Gupta, Siddharth and Narayan, Jagdish}, year={2018}, month={Dec}, pages={3547–3554} }
 @article{bhaumik_sachan_narayan_2017, title={A novel high-temperature carbon-based superconductor: B-doped           Q-carbon}, volume={122}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4994787}, DOI={10.1063/1.4994787}, abstractNote={Following a brief report on high-temperature superconductivity in B-doped Q-carbon [Bhaumik et al., ACS Nano 11(6), 5351–5357 (2017)], we present detailed structure-property correlations to understand the origin of superconductivity in strongly bonded lightweight materials and methods to further enhance the superconducting transition temperature (Tc). Nanosecond melting of carbon in a super undercooled state and rapid quenching result in a strongly bonded unique phase of B-doped Q-carbon. The temperature-dependent resistivity and magnetic susceptibility measurements demonstrate type II superconductivity in this material with a transition temperature of 36.0 ± 0.5 K and an upper critical field of 5.4 T at ∼0 K. It has also been shown that in B-doped Q-carbon, the upper critical magnetic field (Hc2(T)) follows Hc2(0) [1-(T/Tc)2.1] temperature dependence and is consistent with the Bardeen–Cooper–Schrieffer formalism. In the present study, B-doped Q-carbon thin films are formed on sapphire substrates by employing pulsed laser annealing (PLA) using a nanosecond excimer laser. This process involves the rapid quenching of highly undercooled melt of homogenously mixed B and C. Through the structure-property correlation measurements in B-doped Q-carbon, we estimate a higher electronic density of states near the Fermi level. Higher density of states near the Fermi-level along with higher Debye temperature and phonon frequency are responsible for the enhanced Tc. As a result of rapid melting and quenching, we can achieve 17.0 ± 1.0 or higher atomic % of B in the electrically active sites of Q-carbon which leads to the formation of shallow electronic states near the valence band maximum. From the critical current density versus field moments, the value of critical current density (Jc (2T)) in B-doped Q-carbon at 21 K is calculated as 4.3 × 107 A cm−2, which indicates that this novel material can be used for the persistent mode of operation in MRI and nuclear magnetic resonance applications. This discovery of high-temperature superconductivity in B-doped amorphous Q-carbon shows that the non-equilibrium synthesis technique using the super undercooling process can be used to fabricate materials with greatly enhanced physical properties.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2017}, month={Jul}, pages={045301} }
 @article{moatti_sachan_prater_narayan_2017, title={Control of Structural and Electrical Transitions of VO2 Thin Films}, volume={9}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.7b05620}, DOI={10.1021/acsami.7b05620}, abstractNote={Unstrained and defect-free VO2 single crystals undergo structural (from high-temperature tetragonal to low-temperature monoclinic phase) and electronic phase transitions simultaneously. In thin films, however, in the presence of unrelaxed strains and defects, structural (Peierls) and electronic (Mott) transitions are affected differently, and are separated. In this paper, we have studied the temperature dependence of structural and electrical transitions in epitaxially grown vanadium dioxide films on (0001) sapphire substrates. These results are discussed using a combined kinetics and thermodynamics approach, where the velocity of phase transformation is controlled largely by kinetics, and the formation of intermediate phases is governed by thermodynamic considerations. We have grown (020) VO2 on (0001) sapphire with two (001) and (100) in-plane orientations rotated by 122°. The (100)-oriented crystallites are fully relaxed by the paradigm of domain-matching epitaxy, whereas (001) crystallites are not relaxed and exhibit the formation of a few atomic layers of thin interfacial V2O3. We have studied the structural (Peierls) transition by temperature-dependent in situ X-ray diffraction measurements, and electronic (Mott) transition by electrical resistance measurements. A delay of 3 °C is found between the onset of structural (76 °C) and electrical (73 °C) transitions in the heating cycle. This temporal lag in the transition is attributed to the residual strain existing in the VO2 crystallites. With this study, we suggest that the control of structural and electrical transitions is possible by varying the transition activation barrier for atomic jumps through the strain engineering.}, number={28}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Moatti, Adele and Sachan, Ritesh and Prater, John and Narayan, Jay}, year={2017}, month={Jul}, pages={24298–24307} }
 @article{bhaumik_narayan_2017, title={Conversion of p to n-type reduced graphene           oxide by laser annealing at room temperature and pressure}, volume={121}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4979211}, DOI={10.1063/1.4979211}, abstractNote={Physical properties of reduced graphene oxide (rGO) are strongly dependent on the ratio of sp2 to sp3 hybridized carbon atoms and the presence of different functional groups in its structural framework. This research for the very first time illustrates successful wafer scale integration of graphene-related materials by a pulsed laser deposition technique, and controlled conversion of p to n-type 2D rGO by pulsed laser annealing using a nanosecond ArF excimer laser. Reduced graphene oxide is grown onto c-sapphire by employing pulsed laser deposition in a laser MBE chamber and is intrinsically p-type in nature. Subsequent laser annealing converts p into n-type rGO. The XRD, SEM, and Raman spectroscopy indicate the presence of large-area rGO onto c-sapphire having Raman-active vibrational modes: D, G, and 2D. High-resolution SEM and AFM reveal the morphology due to interfacial instability and formation of n-type rGO. Temperature-dependent resistance data of rGO thin films follow the Efros-Shklovskii variable-range-hopping model in the low-temperature region and Arrhenius conduction in the high-temperature regime. The photoluminescence spectra also reveal less intense and broader blue fluorescence spectra, indicating the presence of miniature sized sp2 domains in the vicinity of π* electronic states, which favor the VRH transport phenomena. The XPS results reveal a reduction of the rGO network after laser annealing with the C/O ratio measuring as high as 23% after laser-assisted reduction. The p to n-type conversion is due to the reduction of the rGO framework which also decreases the ratio of the intensity of the D peak to that of the G peak as it is evident from the Raman spectra. This wafer scale integration of rGO with c-sapphire and p to n-type conversion employing a laser annealing technique at room temperature and pressure will be useful for large-area electronic devices and will open a new frontier for further extensive research in graphene-based functionalized 2D materials.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2017}, month={Mar}, pages={125303} }
 @article{bhaumik_sachan_gupta_narayan_2017, title={Discovery of High-Temperature Superconductivity (T-c=55 K) in B-Doped Q-Carbon}, volume={11}, ISSN={["1936-086X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85040089020&partnerID=MN8TOARS}, DOI={10.1021/acsnano.7b06888}, abstractNote={We have achieved a superconducting transition temperature (Tc) of 55 K in 27 at% B-doped Q-carbon. This value represents a significant improvement over previously reported Tc of 36 K in B-doped Q-carbon and is the highest Tc for conventional BCS (Bardeen-Cooper-Schrieffer) superconductivity in bulk carbon-based materials. The B-doped Q-carbon exhibits type-II superconducting characteristics with Hc2(0) ∼ 10.4 T, consistent with the BCS formalism. The B-doped Q-carbon is formed by nanosecond laser melting of B/C multilayered films in a super undercooled state and subsequent quenching. It is determined that ∼67% of the total boron exists with carbon in a sp3 hybridized state, which is responsible for the substantially enhanced Tc. Through the study of the vibrational modes, we deduce that higher density of states near the Fermi level and moderate to strong electron-phonon coupling lead to a high Tc of 55 K. With these results, we establish that heavy B doping in Q-carbon is the pathway for achieving high-temperature superconductivity.}, number={12}, journal={ACS NANO}, author={Bhaumik, Anagh and Sachan, Ritesh and Gupta, Siddharth and Narayan, Jagdish}, year={2017}, month={Dec}, pages={11915–11922} }
 @article{singamaneni_prater_narayan_2017, title={Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures}, volume={7}, ISSN={2158-3226}, url={http://dx.doi.org/10.1063/1.4977071}, DOI={10.1063/1.4977071}, abstractNote={This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ε=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ∼0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature.}, number={5}, journal={AIP Advances}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Prater, John T. and Narayan, Jagdish}, year={2017}, month={May}, pages={055824} }
 @article{narayan_bhaumik_2017, title={Fundamental Discovery of Q-Phases and Direct Conversion of Carbon into Diamond and h-BN into c-BN}, ISBN={["978-3-319-51096-5"]}, ISSN={["2367-1181"]}, DOI={10.1007/978-3-319-51097-2_17}, abstractNote={This article reviews the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and addresses critical issues related to direct conversion of carbon into diamond and h-BN into c-BN at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon and Q-BN are formed as a result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon, and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled (4000 K) carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles and thin films are formed. The large-area epitaxial diamond and c-BN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid state. Scale-up processing of diamond, c-BN and diamond/c-BN heterostructures and related nanostructures such as nanodots, microdots, nanoneedles, microneedles and large-area single-crystal thin films will have tremendous impact on applications ranging from abrasive and tool coatings to high-power devices and myriad of biomedical applications.}, journal={MECHANICAL AND CREEP BEHAVIOR OF ADVANCED MATERIALS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2017}, pages={219–228} }
 @article{bhaumik_sachan_narayan_2017, title={High-Temperature Superconductivity in Boron-Doped Q-Carbon}, volume={11}, ISSN={["1936-086X"]}, DOI={10.1021/acsnano.7b01294}, abstractNote={We report high-temperature superconductivity in B-doped amorphous quenched carbon (Q-carbon). This phase is formed after nanosecond laser melting of B-doped amorphous carbon films in a super-undercooled state and followed by rapid quenching. Magnetic susceptibility measurements show the characteristics of type-II Bardeen-Cooper-Schrieffer superconductivity with a superconducting transition temperature (Tc) of 36.0 ± 0.5 K for 17.0 ± 1.0 atom % boron concentration. This value is significantly higher than the best experimentally reported Tc of 11 K for crystalline B-doped diamond. We argue that the quenching from metallic carbon liquid leads to a stronger electron-phonon coupling due to close packing of carbon atoms with higher density of states at the Fermi level. With these results, we propose that the non-equilibrium undercooling-assisted synthesis method can be used to fabricate highly doped materials that provide greatly enhanced superconducting properties.}, number={6}, journal={ACS NANO}, author={Bhaumik, Anagh and Sachan, Ritesh and Narayan, Jagdish}, year={2017}, month={Jun}, pages={5351–5357} }
 @article{moatti_narayan_2018, title={High-quality TiN/AlN thin film heterostructures on c-sapphire}, volume={145}, ISSN={["1873-2453"]}, url={https://doi.org/10.1016/j.actamat.2017.11.044}, DOI={10.1016/j.actamat.2017.11.044}, abstractNote={We have developed TiN/AlN/c-sapphire epitaxial heterostructures and compared it with TiN/c-sapphire epitaxial heterostructures, needed for GaN-based LEDs and lasers. AlN is used as a buffer layer to provide a high misfit strain and facilitate the 2D growth on sapphire. The large misfit strain between sapphire and AlN makes this substrate a great candidate for GaN-based devices because it guarantees a full relaxation of AlN thin films through domain matching epitaxy paradigm. TiN can also act as an excellent contact and bottom electrode for Ⅲ-Ⅴ nitrides. Also, the introduction of TiN as a buffer layer decreases the critical thickness beyond which dislocations can grow in GaN thin films due to higher misfit strain compared to sapphire, which also improves the quality of potential GaN thin films. The selected-area-electron-diffraction patterns, scanning transmission electron microscopy, and transmission Kikuchi diffractions along with atomic arrangement simulations revealed that films are epitaxial with the following relationships: TiN<101>‖AlN[1¯21¯0]‖sapphire[011¯0] (in-plane), and TiN<111>‖AlN[0001]‖sapphire[0001] (out-of-plane). This is equivalent to a 30° rotation of Al basal plane in AlN with respect to that in sapphire. In TiN/c-sapphire epitaxial platforms, there is a 30° rotation: TiN<101>‖sapphire[011¯0] (in-plane), and TiN<111>‖sapphire[0001] (out-of-plane). It is shown that these heterostructures are fully relaxed in terms of misfit strains and only thermal strain stays as unrelaxed. The domain matching epitaxy paradigm is used to rationalize the epitaxial growth. The details of dislocations nucleation and glide in these heterostructures were studied and the results also discussed to elucidate the mechanism of strain relaxation.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Moatti, A. and Narayan, J.}, year={2018}, month={Feb}, pages={134–141} }
 @article{rasic_sachan_chisholm_prater_narayan_2017, title={Room Temperature Growth of Epitaxial Titanium Nitride Films by Pulsed Laser Deposition}, volume={17}, ISSN={1528-7483 1528-7505}, url={http://dx.doi.org/10.1021/ACS.CGD.7B01278}, DOI={10.1021/ACS.CGD.7B01278}, abstractNote={Reducing the thermal budget of epitaxial thin film growth has been one of the biggest challenges for the electronics industry. In this report, the room-temperature epitaxial growth of titanium nitride (TiN) thin films (∼75 nm) on (0001) Al2O3 substrates is demonstrated using a pulsed laser deposition technique. In TiN thin films, the epitaxial relationship is established by X-ray diffraction for (111)TiN//(0001) Al2O3 and TiN // Al2O3 which corresponds to a 30° rotation of titanium and nitrogen atoms with respect to the hexagon arrangement of aluminum atoms. An increase in the defect concentration is shown in the room-temperature thin film growth as compared to the ones grown at elevated temperature. A shift and broadening of the diffraction peaks is observed in the thin films as compared to the bulk value, indicating a higher residual tensile strain with decreasing growth temperature and an increase in defect concentration at room temperature. The increased defect concentration observed at...}, number={12}, journal={Crystal Growth & Design}, publisher={American Chemical Society (ACS)}, author={Rasic, Daniel and Sachan, Ritesh and Chisholm, Matthew F. and Prater, John and Narayan, Jagdish}, year={2017}, month={Oct}, pages={6634–6640} }
 @article{foley_singamaneni_prater_narayan_2016, title={Control of Magnetic Coercivity in epitaxial Ni/VO2/YSZ/Si(001) heterostructures by manipulation of Ni thin film growth modes}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.397}, abstractNote={The control of ferromagnetic properties by external stimuli is of great interest in the electronics community. One method of producing such a control is through proximity of a ferromagnetic film with a material that has a semiconductor-to-metal transition (SMT). In order for these magnetic heterostructures to be beneficial, they must consist of high-quality, crystalline films. Epitaxial films increase the reproducibility of both devices and properties. We have investigated the trend in magnetic coercivity in epitaxial nickel films on VO_2. We show that not only does the interaction between the Ni and VO_2 change the normal coercivity trend found in Ni M-H curves with no proximity to VO_2, but that the crystalline growth mode of the Ni film also impacts the magnetic coercivity as a function of temperature.}, number={50}, journal={MRS ADVANCES}, author={Foley, Gabrielle M. and Singamaneni, Srinivasa Rao and Prater, John and Narayan, Jay}, year={2016}, pages={3409–3414} }
 @article{temizer_nori_kumar_narayan_2016, title={Defect mediated room temperature ferromagnetism and resistance minima study in epitaxial ZnGa0.002Al0.02O transparent conducting oxide films}, volume={49}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/49/34/345302}, DOI={10.1088/0022-3727/49/34/345302}, abstractNote={We report on the micro-structural, transport, optical and magnetic properties in ZnGa0.002Al0.02O (AGZO) films grown by pulsed laser deposition under different growth conditions. AGZO films grown at substrate temperatures of 600 °C show metal-like behavior with a resistivity minima at lower temperatures, whereas films grown at 300 °C and ambient oxygen partial pressure of 1 mTorr show metallic nature with resistivity values on the order of 100 µΩ · cm at room temperature. The most interesting features are the concomitant occurrence of high temperature resistivity minima and room temperature ferromagnetism with a saturation magnetic moment of 1000 A m−1 and with coercivity in the range 100–240 Oe. The temperature dependent resistivity data has been interpreted in the light of quantum corrections to conductivity in disordered systems, suggesting that the e–e interactions is the dominant mechanism in the weak-localization (WL) limit in the case of films showing resisitivity minima. The simultaneous ferromagnetic ordering coupled with the enhancements in electrical conductivity in AGZO system should have their origin in native point defects in the form of oxygen and zinc vacancies and interstitials and their complexes. We propose that formation of oxygen vacancy–zinc interstitial defect complex (VO–IZn) is responsible for the enhancement in n-type conductivity, and zinc vacancies (VZn) for the observed room temperature ferromagnetism.}, number={34}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Temizer, Namik K and Nori, Sudhakar and Kumar, D and Narayan, Jagdish}, year={2016}, month={Jul}, pages={345302} }
 @article{yamoah_koten_thompson_nannuri_narayan_shield_kumar_2016, title={Dependence of grain size and defect density on the magnetic properties of mechanically alloyed Fe90W10 powder}, volume={120}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4964697}, DOI={10.1063/1.4964697}, abstractNote={Mechanical alloying was used to synthesize nanocrystalline Fe90W10 powders from high purity Fe and W powders. X-ray diffraction measurements showed that the formation of BCC Fe-W solid solution occurred after 32 h of milling. The Scherrer-Debye and Williamson–Hall equations revealed that grain size reduction and defect creation were achieved during the milling process. There is a decrease of grain size from about 53 nm to about 6 nm after 80 h of milling. Williamson and Smallman's equation was also used to calculate the dislocation density. The result shows an increase in the dislocation density with increasing milling time. The grain size and defect characteristics were correlated with magnetic measurements. Magnetization versus magnetic field curves recorded using a vibrating sample magnetometer were utilized to obtain coercivity and saturation magnetization at different temperatures. As W is continually dissolved in the Fe lattice, the change in coercivity seems to be minimal until the completion of solid solution when there is a sudden increase in coercivity. The increase in coercivity is explained by an increase in anisotropy due to an additional source of anisotropy arising from strain during the milling process. There was also a decrease in saturation magnetization as a result of the grain size reduction.}, number={14}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Yamoah, N. K. and Koten, M. A. and Thompson, D. and Nannuri, C. and Narayan, J. and Shield, J. E. and Kumar, D.}, year={2016}, month={Oct}, pages={143903} }
 @article{yamoah_koten_thompson_nannuri_narayan_shield_kumar_2016, title={Dependence of grain size and defect density on the magnetic properties of mechanically alloyed Fe90W10 powder (vol 120, 143903, 2016)}, volume={120}, number={20}, journal={Journal of Applied Physics}, author={Yamoah, N. K. and Koten, M. A. and Thompson, D. and Nannuri, C. and Narayan, J. and Shield, J. E. and Kumar, D.}, year={2016} }
 @article{singamaneni_punugupati_prater_narayan_2016, title={Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films}, volume={108}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4945683}, DOI={10.1063/1.4945683}, abstractNote={We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (∼800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm−1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Punugupati, Sandhyarani and Prater, John T. and Narayan, Jagdish}, year={2016}, month={Apr}, pages={142407} }
 @article{narayan_bhaumik_xu_2016, title={Direct conversion of h-BN into c-BN and formation of epitaxial c-BN/diamond heterostructures}, volume={119}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4948688}, DOI={10.1063/1.4948688}, abstractNote={We have created a new state of BN (named Q-BN) through rapid melting and super undercooling and quenching by using nanosecond laser pulses. Phase pure c-BN is formed either by direct quenching of super undercooled liquid or by nucleation and growth from Q-BN. Thus, a direct conversion of hexagonal boron nitride (h-BN) into phase-pure cubic boron nitride (c-BN) is achieved by nanosecond pulsed laser melting at ambient temperatures and atmospheric pressure in air. According to the P-T phase diagram, the transformation from h-BN into c-BN under equilibrium processing can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa or 3700 K/7.0 GPa with a recent theoretical refinement. Using nonequilibrium nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to the formation of a new phase, named as Q-BN. We present detailed characterization of Q-BN and c-BN layers by using Raman spectroscopy, high-resolution scanning electron microscopy, electron-back-scatter diffraction, high-resolution TEM, and electron energy loss spectroscopy, and discuss the mechanism of formation of nanodots, nanoneedles, microneedles, and single-crystal c-BN on sapphire substrate. We have also deposited diamond by pulsed laser deposition of carbon on c-BN and created c-BN/diamond heterostructures, where c-BN acts as a template for epitaxial diamond growth. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon, and the impact of this discovery on a variety of applications.}, number={18}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, Jagdish and Bhaumik, Anagh and Xu, Weizong}, year={2016}, month={May}, pages={185302} }
 @article{narayan_bhaumik_2016, title={Discovery of Q-BN and Direct Conversion of h-BN into c-BN and Formation of Epitaxial cBN/Diamond Heterostructures}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.472}, abstractNote={We review the discovery of a new phase BN (named Q-BN) which has been created by nanosecond laser melting in the super undercooled state and quenching rapidly with rates exceeding several billion degrees per second. This phase, sequel to our earlier discovery of Q-Carbon, has amorphous structure from which phase-pure c-BN is formed in the form of nanodots, microcrystals, nanoneedles, and microneedles. Large-area single c-BN are formed by providing a template for epitaxial growth during quenching of super undercooled liquid BN. Since there is a rapid crystal growth from liquid, both n- and p-type dopants can be incorporated into electrically active substitutional sites with concentrations exceeding solubility limits through the phenomenon of solute trapping. We have grown diamond on c-BN by pulsed laser deposition of carbon at 500°C without the presence of hydrogen, and created c-BN and diamond epitaxial composites. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon. This discovery on direct conversion of h-BN into phase-pure c-BN at ambient temperatures and pressures in air, represents a seminal contribution to the field of boron nitride, which is quite complementary to our discovery of graphite to diamond conversion. We have bypassed thermodynamics with the help of kinetics and time control. This research represents a major breakthrough for c-BN and diamond based high-power electronic and photonic devices, and host of other applications related to high-speed machining, deep-sea drilling, field-emission displays and biomedical applications.}, number={37}, journal={MRS ADVANCES}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, pages={2573–2584} }
 @article{narayan_bhaumik_narayan_2016, title={Discovery of Q-phases and direct conversion of carbon into diamond and h-BN into c-BN}, volume={174}, number={3}, journal={Advanced Materials & Processes}, author={Narayan, J. and Bhaumik, A. and Narayan, R.}, year={2016}, pages={24–28} }
 @article{singamaneni_prater_narayan_2016, title={Enhanced Coercivity in BiFeO3/SrRuO3 heterostructures}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.220}, abstractNote={Transition metal oxide thin film heterostructures have garnered increasing research interest in the last decade due to their multifunctional properties, such as ferromagnetism and ferroelectricity, which may be utilized in next generation device applications. Many previous works reported on the deposition of such structures on oxide substrates such as SrTiO_3, which are not compatible with CMOS applications where Si(100) is the mainstay substrate material . BiFeO_3 (BFO) is a room temperature insulating ferroelectric and antiferromagnet, a well-known multiferroic material. SrRuO_3 (SRO) is a ferromagnetic metal with the Curie temperature (T_C) of 165K. Unexpected properties emerge when these two dissimilar materials are conjoined. However, there has been no report on exploring the magnetic properties of BFO when it is in contact with SRO, and particularly when they are integrated with Si(100) substrates, which is the subject of present study. BFO/SRO thin films have been epitaxially grown on Si (100) substrates by introducing MgO/TiN epitaxial buffer layers using pulsed laser deposition. BFO thin films show room temperature ferroelectricity as observed from piezo force microscopy (PFM) measurements. The magnetic data collected from BFO thin films show typical antiferromagnetic features as expected. The T_C of SRO in all the samples studied was found be ~ 170K, close to the reported value of 165K. Interestingly, we have noticed that the coercive field of SRO layer increased from 4 kOe to 15 kOe (nearly fourfold) by reducing its thickness from 180 to 23nm, while keeping the thickness of BFO layer constant at 100nm. Pinning of Ru ions by ferroelectric domain walls in BFO, strong interfacial exchange coupling and SRO layer thickness could cause the observed enhancement in coercivity. Our near future work will address the precise underlying mechanisms in greater detail.}, number={9}, journal={MRS ADVANCES}, author={Singamaneni, Srinivasa Rao and Prater, J. T. and Narayan, J.}, year={2016}, pages={597–602} }
 @article{moatti_bayati_singamaneni_narayan_2016, title={Epitaxial integration of TiO2 with Si(100) through a novel approach of oxidation of TiN/Si(100) epitaxial heterostructure}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.463}, abstractNote={In this study, we provide a novel approach to the epitaxial integration of TiO_2 with Si(100) and investigate the defect mediated ferromagnetism in TiO_2 structure. Epitaxial TiO_2 thin films were grown on a TiN/Si(100) epitaxial heterostructure through oxidation of TiN where a single crystalline rutile-TiO_2 (r-TiO_2) with a [110] out-of-plane orientation was obtained. The epitaxial relationship is determined to be TiO_2(1 $\overline 1 $ 0)||TiN(100) and TiO_2(110)||TiN(110). We rationalized this epitaxy using the domain matching epitaxy paradigm. First TiN is grown epitaxially on Si(100). Subsequently, TiN/Si(100) samples are oxidized to create r-TiO_2/TiN/Si(100) epitaxial heterostructures. The details of the mechanism behind the oxidation of single crystalline TiN to TiO_2 was investigated using atomic scale high resolution electron microscopy techniques. Defects introduced to the heterostructure during oxidation caused ferromagnetism in TiO_2 thin film which is reversible and can be tuned by controlling oxygen partial pressure. The source of magnetization is correlated with the presence of oxygen vacancy leading to introduction of two localized states; hybrid and polaron among neighboring Ti atoms, and titanium vacancy providing four holes to form molecular oxygen. We present structure property correlations and its impact on the next generation solid state devices.}, number={37}, journal={MRS ADVANCES}, author={Moatti, A. and Bayati, R. and Singamaneni, S. and Narayan, J.}, year={2016}, pages={2629–2634} }
 @article{singamaneni_prater_wu_narayan_2016, title={Ferromagnetic oxide heterostructures on silicon}, volume={6}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2016.22}, abstractNote={Heterostructures consisting of two ferromagnetic oxides La_0.7Ca_0.3MnO_3 (LCMO) and SrRuO_3 (SRO) were epitaxially grown by pulsed laser deposition onto a silicon (Si) substrate buffered by SrTiO_3 (STO)/MgO/TiN. The x-ray scans and electron-diffraction patterns reveal the epitaxial nature of all five layers. From transmission electron microscopy, the thicknesses of the LCMO and SRO layers were estimated to be -100 and -200 nm, respectively. The magnetic properties of individual SRO and LCMO layers are in good agreement with the previous studies reported for those individual layers deposited on lattice-matched substrates, such as STO. The LCMO/SRO heterostructures showed enhanced switching field (from 6008 to 7600 Oe), which may originate from the bulk part of the heterostructure. The ability to grow these multifunctional structures on Si provides a route for wafer scale integration with Si, in contrast to oxide substrates that are not suitable for CMOS integration for microelectronics and spintronics applications.}, number={3}, journal={MRS COMMUNICATIONS}, author={Singamaneni, Srinivasa Rao and Prater, J. T. and Wu, Fan and Narayan, J.}, year={2016}, month={Sep}, pages={234–240} }
 @article{narayan_bhaumik_2016, title={Fundamental discovery of new phases and direct conversion of carbon into diamond and hBN into cBN and properties (retraction of vol 47, pg 1481, 2016)}, volume={47A}, number={8}, journal={Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science}, author={Narayan, J. and Bhaumik, A.}, year={2016}, pages={4351–4351} }
 @article{ma_huang_moering_ruppert_hoeppel_goeken_narayan_zhu_2016, title={Mechanical properties of copper/bronze laminates: Role of interfaces}, volume={116}, ISSN={["1873-2453"]}, url={https://doi.org/10.1016/j.actamat.2016.06.023}, DOI={10.1016/j.actamat.2016.06.023}, abstractNote={Interfaces play a crucial role in mechanical behaviors of both laminated and gradient structured materials. In this work, copper/bronze laminates with varying interface spacing were fabricated by accumulative roll bonding and subsequent annealing to systematically study the interface effect on mechanical properties. Heterogeneities exist in chemical composition, grain size, hardness and texture across the interfaces. Simultaneous improvement of strength and ductility with decreasing interface spacing is found in tensile tests. Extra geometrically necessary dislocations (GNDs) are found to accumulate in the vicinity of interfaces, which is due to mechanical incompatibility across the interfaces. Importantly, an interface-affected zone spanning a few micrometers was found, which is not affected by interface spacing. These observations suggest the existence of an optimum spacing, which may produce the highest hardening capacity and ductility without sacrificing strength.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Ma, Xiaolong and Huang, Chongxiang and Moering, Jordan and Ruppert, Mathis and Hoeppel, Heinz Werner and Goeken, Mathias and Narayan, Jagdish and Zhu, Yuntian}, year={2016}, month={Sep}, pages={43–52} }
 @article{singamaneni_prater_lee_misra_narayan_2016, title={Memristive behavior in BaTiO3/La0.7Sr0.3MnO3 heterostructures integrated with semiconductors}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.70}, abstractNote={Ferroelectric materials such as BaTiO_3 have been studied for emerging non-volatile memory applications. However, most of the previous work has been focused on this material when it was deposited on insulting oxide substrates such as SrTiO_3. Unfortunately, this substrate is not suitable for CMOS-based microelectronics applications. This motivated us to carry out the present work. We have studied the resistive switching behavior in BaTiO_3/La_0.7Sr_0.3MnO_3 (BTO/LSMO) heterostructures integrated with semiconducting substrates Si (100) using MgO/TiN buffer layers by pulsed laser deposition. Current-Voltage (I-V) measurements were conducted on BTO (500nm)/LSMO (25nm) devices at 200K. We have observed a broad hysteresis in forward and reverse voltage sweeps which is an important property for memory applications. Secondly, the R_ON/R_OFF ratio is estimated at ~ 150, consistent with the reported numbers (30-100) in the literature. Thirdly, the device is stable at least up to 50 cycles. However, we found that hysteretic behavior was suppressed upon oxygen annealing of the device at 1 atmospheric pressure, 200^o C for 1hr, inferring the important role of oxygen vacancies in the resistive switching behavior of BTO/LSMO device. Future work will focus on investigating the correlation between ferroelectricity and resistive switching in these devices using local probe technique piezo force microscopy (PFM) technique.}, number={4}, journal={MRS ADVANCES}, author={Singamaneni, Srinivasa Rao and Prater, John and Lee, Bongmook and Misra, Veena and Narayan, Jay}, year={2016}, pages={275–280} }
 @article{nellutla_nori_singamaneni_prater_narayan_smirnov_2016, title={Multi-frequency ferromagnetic resonance investigation of nickel nanocubes encapsulated in diamagnetic magnesium oxide matrix}, volume={120}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4971869}, DOI={10.1063/1.4971869}, abstractNote={Partially aligned nickel nanocubes were grown epitaxially in a diamagnetic magnesium oxide (MgO:Ni) host and studied by a continuous wave ferromagnetic resonance (FMR) spectroscopy at the X-band (9.5 GHz) from ca. 117 to 458 K and then at room temperature for multiple external magnetic fields/resonant frequencies from 9.5 to 330 GHz. In contrast to conventional magnetic susceptibility studies that provided data on the bulk magnetization, the FMR spectra revealed the presence of three different types of magnetic Ni nanocubes in the sample. Specifically, three different ferromagnetic resonances were observed in the X-band spectra: a line 1 assigned to large nickel nanocubes, a line 2 corresponding to the nanocubes exhibiting saturated magnetization even at ca. 0.3 T field, and a high field line 3 (geff ∼ 6.2) tentatively assigned to small nickel nanocubes likely having their hard magnetization axis aligned along or close to the direction of the external magnetic field. Based on the analysis of FMR data, the latter nanocubes possess an anisotropic internal magnetic field of at least ∼1.0 T in magnitude.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Nellutla, Saritha and Nori, Sudhakar and Singamaneni, Srinivasa R. and Prater, John T. and Narayan, Jagdish and Smirnov, Alex I.}, year={2016}, month={Dec}, pages={223902} }
 @article{singamaneni_prater_narayan_2016, title={Multifunctional epitaxial systems on silicon substrates}, volume={3}, ISSN={1931-9401}, url={http://dx.doi.org/10.1063/1.4955413}, DOI={10.1063/1.4955413}, abstractNote={Multifunctional heterostructures can exhibit a wide range of functional properties, including colossal magneto-resistance, magnetocaloric, and multiferroic behavior, and can display interesting physical phenomena including spin and charge ordering and strong spin-orbit coupling. However, putting this functionality to work remains a challenge. To date, most of the work reported in the literature has dealt with heterostructures deposited onto closely lattice matched insulating substrates such as DyScO3, SrTiO3 (STO), or STO buffered Si(100) using concepts of lattice matching epitaxy (LME). However, strain in heterostructures grown by LME is typically not fully relaxed and the layers contain detrimental defects such as threading dislocations that can significantly degrade the physical properties of the films and adversely affect the device characteristics. In addition, most of the substrates are incompatible with existing CMOS-based technology, where Si (100) substrates dominate. This review discusses recent advances in the integration of multifunctional oxide and non-oxide materials onto silicon substrates. An alternative thin film growth approach, called “domain matching epitaxy,” is presented which identifies approaches for minimizing lattice strain and unwanted defects in large misfit systems (7%–25% and higher). This approach broadly allows for the integration of multifunctional materials onto silicon substrates, such that sensing, computation, and response functions can be combined to produce next generation “smart” devices. In general, pulsed laser deposition has been used to epitaxially grow these materials, although the concepts developed here can be extended to other deposition techniques, as well. It will be shown that TiN and yttria-stabilized zirconia template layers provide promising platforms for the integration of new functionality into silicon-based computer chips. This review paper reports on a number of thin-film heterostructure systems that span a variety of ferroelectric, multiferroic, magnetic, photocatalytic, and smart materials. Their properties have been extensively investigated and their functionality found to be comparable to films grown on single-crystal oxide substrates previously reported by researchers in this field. In addition, this review explores the utility of using laser processing to introduce stable defects in a controlled way and induce magnetism and engineer the optical and electrical properties of nonmagnetic oxides such as BaTiO3, VO2, NiO, and TiO2 as an alternative for incorporating additional magnetic and conducting layers into the structure. These significant materials advancements herald a flurry of exciting new advances in CMOS-compatible multifunctional devices.}, number={3}, journal={Applied Physics Reviews}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Prater, John Thomas and Narayan, Jagdish}, year={2016}, month={Sep}, pages={031301} }
 @article{narayan_bhaumik_2017, title={Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures}, volume={5}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2016.1249805}, abstractNote={ABSTRACT We report a novel method for synthesis and processing of pure and nitrogen-vacancy (NV)-doped nanodiamonds with sharp NV0 and NV− transitions at ambient temperatures and pressures in air. Carbon films are melted by nanosecond lasers in super undercooled state and quenched rapidly. We can form single-crystal nanodiamonds, microdiamonds, nanoneedles and microneedles, and large-area films. Substitutional nitrogen atoms and vacancies are incorporated into diamond during rapid liquid-phase growth, where dopant concentrations can far exceed thermodynamic solubility limits through solute trapping. These nanodiamonds can be placed deterministically and the transitions between NV− and NV0 can be controlled electrically and optically by laser illumination. GRAPHICAL ABSTRACT IMPACT STATEMENT This research represents a fundamental breakthrough in controlled synthesis of nanodiamonds and doping of diamond with NV centers in nanostructures needed for quantum devices operating at room temperature.}, number={4}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2017}, pages={242–250} }
 @article{yamoah_koten_thompson_nannuri_narayan_shield_kumar_2016, title={Publisher's Note: “Dependence of grain size and defect density on the magnetic properties of mechanically alloyed Fe90W10 powder” [J. Appl. Phys. 120, 143903 (2016)]}, volume={120}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4967924}, DOI={10.1063/1.4967924}, abstractNote={First Page}, number={20}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Yamoah, N. K. and Koten, M. A. and Thompson, D. and Nannuri, C. and Narayan, J. and Shield, J. E. and Kumar, D.}, year={2016}, month={Nov}, pages={209901} }
 @article{narayan_bhaumik_2016, title={Q-carbon discovery and formation of single-crystal diamond nano- and microneedles and thin films}, volume={4}, ISSN={["2166-3831"]}, DOI={10.1080/21663831.2015.1126865}, abstractNote={We report the formation of single-crystal diamond nanoneedles, microneedles and thin films on sapphire (0001). By using nanosecond excimer laser pulses, we convert amorphous carbon into a new state of Q-carbon by rapid melting and quenching. The Q-carbon consists of amorphous mostly sp3 bonded carbon and rest 10–15% sp2, from which diamonds are nucleated. These nanodiamond nuclei in Q-carbon provide a seed for growth of diamond. These nanoneedles and microneedles are found to be single crystals often oriented along ⟨110⟩ directions. The (111) single-crystal diamond film are formed, when sapphire (0001) provides a seed for diamond growth from super undercooled liquid. GRAPHICAL ABSTRACT}, number={2}, journal={MATERIALS RESEARCH LETTERS}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, pages={118–126} }
 @article{narayan_bhaumik_2016, title={RETRACTED ARTICLE: Fundamental Discovery of New Phases and Direct Conversion of Carbon into Diamond and hBN into cBN and Properties}, volume={47}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/S11661-015-3312-7}, DOI={10.1007/S11661-015-3312-7}, number={4}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, month={Jan}, pages={1481–1498} }
 @article{narayan_bhaumik_2016, title={Research Update: Direct conversion of h-BN into pure c-BN at ambient temperatures and pressures in air}, volume={4}, ISSN={2166-532X}, url={http://dx.doi.org/10.1063/1.4941095}, DOI={10.1063/1.4941095}, abstractNote={We report a direct conversion of hexagonal boron nitride (h-BN) into pure cubic boron nitride (c-BN) by nanosecond laser melting at ambient temperatures and atmospheric pressure in air. According to the phase diagram, the transformation from h-BN into c-BN can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa. Using nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to formation of super undercooled BN (Q-BN). The c-BN phase is nucleated from Q-BN depending upon the time allowed for nucleation and growth.}, number={2}, journal={APL Materials}, publisher={AIP Publishing}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, month={Feb}, pages={020701} }
 @article{narayan_bhaumik_2016, title={Retraction Note to: Fundamental Discovery of New Phases and Direct Conversion of Carbon into Diamond and hBN into cBN and Properties}, volume={47}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/S11661-016-3566-8}, DOI={10.1007/S11661-016-3566-8}, abstractNote={We review the discovery of new phases of carbon (Q-carbon) and BN (Q-BN)
 and address critical issues related to direct conversion of carbon into diamond and
 hBN into cBN at ambient temperatures and pressures in air without any need for
 catalyst and the presence of hydrogen. The Q-carbon and Q-BN are formed as a result
 of quenching from super undercooled state by using high-power nanosecond laser
 pulses. We discuss the equilibrium phase diagram (P
 vs
 T) of carbon, and show that by rapid quenching,
 kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from
 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. Similarly,
 the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K
 and atmospheric pressure. It is shown that nanosecond laser heating of amorphous
 carbon and nanocrystalline BN on sapphire, glass, and polymer substrates can be
 confined to melt in a super undercooled state. By quenching this super undercooled
 state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which
 nanocrystals, microcrystals, nanoneedles, microneedles, and thin films are formed
 depending upon the nucleation and growth times allowed and the presence of growth
 template. The large-area epitaxial diamond and cBN films are formed, when
 appropriate planar matching or lattice matching template is provided for growth from
 super undercooled liquid. The Q-phases have unique atomic structure and bonding
 characteristics as determined by high-resolution SEM and backscatter diffraction,
 HRTEM, STEM-Z, EELS, and Raman spectroscopy, and exhibit new and improved mechanical
 hardness, electrical conductivity, and chemical and physical properties, including
 room-temperature ferromagnetism and enhanced field emission. The Q-carbon exhibits
 robust bulk ferromagnetism with estimated Curie temperature of about 500 K and
 saturation magnetization value of 20 emu g−1. We have
 also deposited diamond on cBN by using a novel pulsed laser evaporation of carbon
 and obtained cBN/diamond composites, where cBN acts as template for diamond growth.
 Both diamond and cBN grown from super undercooled liquid can be alloyed with both p-
 and n-type dopants. This process allows carbon to diamond and hBN to cBN conversions
 and formation of useful nanostructures and microstructures at ambient temperatures
 in air at atmospheric pressure on practical and heat-sensitive substrates in a
 controlled way without need for any catalysts and hydrogen to stabilize
 sp3 bonding for diamond and cBN phases.}, number={8}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, month={May}, pages={4351–4351} }
 @article{chen_zhou_zhu_li_zhang_narayan_wang_jia_2016, title={Stabilizing new bismuth compounds in thin film form}, volume={31}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2016.391}, abstractNote={Abstract}, number={22}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Chen, Aiping and Zhou, Honghui and Zhu, Yuanyuan and Li, Leigang and Zhang, Wenrui and Narayan, Jagdish and Wang, Haiyan and Jia, Quanxi}, year={2016}, month={Nov}, pages={3530–3537} }
 @article{punugupati_kumar_nori_hunte_narayan_2016, title={Structural, magnetic and magnetotransport properties of bi-epitaxial La0.7Sr0.3MnO3 (110) thin films integrated on Si (001)}, volume={106}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2015.12.054}, abstractNote={We report the growth of bi-epitaxial La0.7Sr0.3MnO3 (110) thin films on Si (001) substrate with cubic yttria stabilized zirconia (c-YSZ)/SrTiO3 (STO) buffer layers by pulsed laser deposition. The La0.7Sr0.3MnO3 and STO thin films were grown with a single [110] out-of-plane orientation and with two in-plane domain variants, which is confirmed by XRD and detailed TEM studies. The growth of STO on c-YSZ can be explained by the paradigm of domain matching epitaxy. The epitaxial relationship between STO and c-YSZ can be written as [110] (001) c-YSZ ‖ [1¯11¯] (110) STO (or) [110] (001) c-YSZ ‖ [1¯12¯] (110) STO. The La0.7Sr0.3MnO3 thin films are ferromagnetic with Curie temperature 324 K and showed metal to insulator transition at 285 K. The La0.7Sr0.3MnO3 thin films showed hysteresis loops in magnetoresistance when magnetic field is applied along both in-plane (110) and out-of-plane [110] directions. The highest magnetoresistance obtained in this study is −32% at 50 K and 50 kOe for in-plane configuration, whereas the room-temperature magnetoresistance is −4% at 10 kOe and −17% at 50 kOe. The hysteresis in the magnetoresistance and the controlled domain boundaries in bi-epitaxial La0.7Sr0.3MnO3 films integrated on Si can offer significant advantages over the polycrystalline counterparts.}, journal={ACTA MATERIALIA}, author={Punugupati, Sandhyarani and Kumar, Raj and Nori, Sudhakar and Hunte, Frank and Narayan, Jagdish}, year={2016}, month={Mar}, pages={40–47} }
 @article{moatti_bayati_singamaneni_narayan_2016, title={Thin film bi-epitaxy and transition characteristics of TiO2/TiN buffered VO2 on Si(100) substrates}, volume={1}, ISSN={["2059-8521"]}, DOI={10.1557/adv.2016.544}, abstractNote={Bi-epitaxial VO_2 thin films with [011] out-of-plane orientation were integrated with Si(100) substrates through TiO_2/TiN buffer layers. At the first step, TiN is grown epitaxially on Si(100), where a cube-on-cube epitaxy is achieved. Then, TiN was oxidized in-situ ending up having epitaxial r-TiO_2. Finally, VO_2 was deposited on top of TiO_2. The alignment across the interfaces was stablished as VO_2(011)║TiO_2(110)║TiN(100)║Si(100) and VO_2(110) /VO_2(010)║TiO_2(011)║TiN(112)║Si(112). The inter-planar spacing of VO_2(010) and TiO_2(011) equal to 2.26 and 2.50 Å, respectively. This results in a 9.78% tensile misfit strain in VO_2(010) lattice which relaxes through 9/10 alteration domains with a frequency factor of 0.5, according to the domain matching epitaxy paradigm. Also, the inter-planar spacing of VO_2(011) and TiO_2(011) equals to 3.19 and 2.50 Å, respectively. This results in a 27.6% compressive misfit strain in VO_2(011) lattice which relaxes through 3/4 alteration domains with a frequency factor of 0.57. We studied semiconductor to metal transition characteristics of VO_2/TiO_2/TiN/Si heterostructures and established a correlation between intrinsic defects and magnetic properties.}, number={37}, journal={MRS ADVANCES}, author={Moatti, Adele and Bayati, Reza and Singamaneni, Srinivasa Rao and Narayan, Jagdish}, year={2016}, pages={2635–2640} }
 @article{zhang_li_chen_li_zhu_xia_lu_boullay_wu_zhu_et al._2016, title={Two-Dimensional Layered Oxide Structures Tailored by Self Assembled Layer Stacking via Interfacial Strain}, volume={8}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.6b03773}, abstractNote={Study of layered complex oxides emerge as one of leading topics in fundamental materials science because of the strong interplay among intrinsic charge, spin, orbital, and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials that exhibit new phenomena beyond their conventional forms. Here, we report a strain-driven self-assembly of bismuth-based supercell (SC) with a two-dimensional (2D) layered structure. With combined experimental analysis and first-principles calculations, we investigated the full SC structure and elucidated the fundamental growth mechanism achieved by the strain-enabled self-assembled atomic layer stacking. The unique SC structure exhibits room-temperature ferroelectricity, enhanced magnetic responses, and a distinct optical bandgap from the conventional double perovskite structure. This study reveals the important role of interfacial strain modulation and atomic rearrangement in self-assembling a layered singe-phase multiferroic thin film, which opens up a promising avenue in the search for and design of novel 2D layered complex oxides with enormous promise.}, number={26}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Zhang, Wenrui and Li, Mingtao and Chen, Aiping and Li, Leigang and Zhu, Yuanyuan and Xia, Zhenhai and Lu, Ping and Boullay, Philippe and Wu, Lijun and Zhu, Yimei and et al.}, year={2016}, month={Jul}, pages={16845–16851} }
 @article{narayan_bhaumik_2016, title={WITHDRAWN: Discovery of Q-carbon, ferromagnetism and conversion into diamond}, volume={1}, ISSN={1359-0286}, url={http://dx.doi.org/10.1016/J.COSSMS.2016.01.001}, DOI={10.1016/J.COSSMS.2016.01.001}, abstractNote={This article has been withdrawn: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been withdrawn at the request of the Editor and the Publisher, as the article contains a significant amount of material duplicated from the articles: Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air, APL Materials, 3, 100702 (2015); Novel phase of carbon, ferromagnetism, and conversion into diamond, Journal of Applied Physics, 118, 215303 (2015).}, journal={Current Opinion in Solid State and Materials Science}, publisher={Elsevier BV}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2016}, month={Jan} }
 @article{bhaumik_narayan_2016, title={Wafer scale integration of reduced graphene oxide by novel laser processing at room temperature in air}, volume={120}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4962210}, DOI={10.1063/1.4962210}, abstractNote={Physical properties of reduced graphene oxide (rGO) strongly depend on the ratio of sp2 to sp3 hybridized carbon atoms, the presence of different functional groups, and the characteristics of the substrates. This research for the very first time illustrates successful wafer scale integration of 2D rGO with Cu/TiN/Si, employing pulsed laser deposition followed by laser annealing of carbon-doped copper layers using nanosecond excimer lasers. The XRD, SEM, and Raman spectroscopy measurements indicate the presence of large area rGO onto Si having Raman active vibrational modes: D, G, and 2D. A high resolution SEM depicts the morphology and formation of rGO from zone-refined carbon formed after nanosecond laser annealing. Temperature-dependent resistance data of rGO thin films follow the Efros-Shklovskii variable range hopping (VRH) model in the low-temperature region and Arrhenius conduction in the high-temperature regime. The photoluminescence spectra also reveal a less intense and broader blue fluorescence spectra, indicating the presence of miniature sized sp2 domains in the near vicinity of π* electronic states which favor the VRH transport phenomena. This wafer scale integration of rGO with Si employing a laser annealing technique will be useful for multifunctional integrated electronic devices and will open a new frontier for further extensive research in these functionalized 2D materials.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhaumik, Anagh and Narayan, Jagdish}, year={2016}, month={Sep}, pages={105304} }
 @article{ma_xu_zhou_moering_narayan_zhu_2015, title={Alloying effect on grain-size dependent deformation twinning in nanocrystalline Cu-Zn alloys}, volume={95}, ISSN={["1478-6443"]}, DOI={10.1080/14786435.2014.1000418}, abstractNote={Grain-size dependency of deformation twinning has been previously reported in nanocrystalline face-centred-cubic metals, which results in an optimum grain-size range for twin formation. Here, we report, for the first time in experiments, the observed optimum grain sizes for deformation twins in nanocrystalline Cu–Zn alloys which slightly increase with increasing Zn content. This result agrees with the reported trend but is much weaker than predicted by stacking-fault-energy based models. Our results indicate that alloying changes the relationship between the stacking-fault and twin-fault energy and therefore affects the optimum grain size for deformation twinning. These observations should be also applicable to other alloy systems.}, number={3}, journal={PHILOSOPHICAL MAGAZINE}, author={Ma, X. L. and Xu, W. Z. and Zhou, H. and Moering, J. A. and Narayan, J. and Zhu, Y. T.}, year={2015}, month={Jan}, pages={301–310} }
 @article{singamaneni_fan_prater_narayan_2015, title={Complete vertical M-H loop shift in La0.7Sr0.3MnO3/SrRuO3 thin film heterostructures}, volume={117}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4913630}, DOI={10.1063/1.4913630}, abstractNote={In the current work, we have epitaxially integrated La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) BLs with the technologically important substrate Si (100) using pulsed laser deposition. Interestingly, at 4 K, under the magnetic field sweep of ±1500 Oe, a complete vertical M-H loop shift is observed in the sample prepared with 180 nm SRO thickness, which is unusual. This vertical shift persists even up to a field sweep range of ±6000 Oe, at which point the shift disappears and a symmetrical hysteresis loop centered at the origin is observed. In contrast, at the same temperature, under the same field sweep range, we observe a normal M-H loop (no or little vertical shift) from the sample with 45 nm SRO thickness. In both the cases, the LSMO thickness was held constant at ∼100 nm. It appears that SRO moment is frozen in place in the latter case, providing a clear demonstration of the effect that biasing layer (SRO) thickness can have on the magnetic characteristics of bilayer films. We attribute this vertical shift to the strong interplay between the uniaxial magnetocrystalline anisotropy and microscopic interface domain structure.}, number={17}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Fan, Wu and Prater, J. T. and Narayan, J.}, year={2015}, month={May}, pages={17B711} }
 @article{lee_kumar_hunte_narayan_schwartz_2015, title={Control of intrinsic defects and magnetotransport properties of Bi2Se3/c-sapphire epitaxial heterostructures}, volume={95}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/J.ACTAMAT.2015.05.009}, DOI={10.1016/j.actamat.2015.05.009}, abstractNote={We have synthesised Bi2Se3 epitaxial thin films on c-sapphire substrates, where Se-related defects and strains are controlled precisely during pulsed laser deposition. This allows us to tune electrical and magnetotransport properties and probe the role of defects and strains as a function of processing conditions systematically. The defect microstructure has been studied in detail using high resolution X-ray diffraction and high-angle annular dark field scanning transmission electron microscopy. Magnetotransport measurements show a strong dependence on microstructure which is associated with the Se-content. With higher Se content, the film experiences large compressive strain along the [0 0 1] direction which is accompanied by the partial suppression of one family of twin domain formation. As a result, the insulating behavior becomes more pronounced at a low temperature which is understood in terms of the quantum correlation induced by electron–electron interactions. The compressive strain enhances spin–orbit coupling and topological characteristics. These results shed light on the importance of controlling the intrinsic defects during the growth of Bi2Se3 thin films, providing an effective way to suppress the bulk conductivity and establish the correlation between microstructure and strain.}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Lee, Y.F. and Kumar, R. and Hunte, F. and Narayan, J. and Schwartz, J.}, year={2015}, month={Aug}, pages={57–64} }
 @article{bayati_molaei_wu_narayan_yarmolenko_2015, title={Dependence of Semiconductor to Metal Transition of VO2(011)/NiO{100}/MgO{100}/TiN{100}/Si{100} Heterostructures on Thin Film Epitaxy and Nature of Strain}, volume={98}, number={4}, journal={Journal of the American Ceramic Society}, author={Bayati, Reza and Molaei, Roya and Wu, Fan and Narayan, Jagdish and Yarmolenko, Sergey}, year={2015}, month={Apr}, pages={1201–1208} }
 @article{moatti_bayati_narayan_2016, title={Epitaxial growth of rutile TiO2 thin films by oxidation of TiN/Si{100} heterostructure}, volume={103}, ISSN={["1873-2453"]}, url={https://doi.org/10.1016/j.actamat.2015.10.022}, DOI={10.1016/j.actamat.2015.10.022}, abstractNote={We have integrated epitaxial TiO2 on a TiN/Si(100) platform through oxidation of TiN. The oxidation of TiN(100)/Si(100) results in the formation of an epitaxial rutile-TiO2 (r-TiO2) with a [110] out-of-plane orientation. We have studied in detail the r-TiO2 epitaxy and the epitaxial relationship is determined to be TiO2(11¯0)||TiN(100) and TiO2(110)||TiN(110). We rationalized this epitaxy using the domain matching epitaxy paradigm. Below the r-TiO2 epitaxial layer, we observed cuboids, which are mostly voids. We described the mechanism of oxidation where Ti out diffusion during oxidation leads to collapse of the nitrogen octahedron. This collapse makes neighboring Ti bonds weaker, promoting these Ti atoms to diffuse out next. Thus, cuboids filled with atomic nitrogen are formed, which then form N2 gas. The N2 pressure in these cuboids was estimated to be as high as 359 MPa, assuming all N2 is retained in the cuboids. This pressure can exceed the fracture stress of TiO2 and leads to rupture of thin TiO2 surface, which has been observed under certain conditions.}, journal={ACTA MATERIALIA}, publisher={Elsevier BV}, author={Moatti, A. and Bayati, R. and Narayan, J.}, year={2016}, month={Jan}, pages={502–511} }
 @article{wu_zheng_cai_yao_zhu_narayan_2015, title={Fabrication of epitaxial Cu3Ge on sapphire with controlled crystallinity and planar defects}, volume={641}, ISSN={["1873-4669"]}, DOI={10.1016/j.jallcom.2015.03.143}, abstractNote={In this paper, we report the growth of epitaxial Cu3Ge thin films on c-plane sapphire substrate through domain matching epitaxy. Systematic study on the crystallinity of Cu3Ge thin films is carried out to correlate epitaxial characteristics with substrate lattice misfit. The crystallinity and epitaxy of the as-grown Cu3Ge thin films are improved considerably by controlling the parameters of pulsed laser deposition. The epitaxial characteristics and formation of twins in Cu3Ge are investigated and a mechanism of twin formation in Cu3Ge ε1-phase is discussed. The present study proves that the crystallinity and defect structure of Cu3Ge thin film can be controlled by adjusting the deposition parameters. It serves as a fundamental research for future applications of epitaxial Cu3Ge as metallization material in semiconductor industry.}, journal={JOURNAL OF ALLOYS AND COMPOUNDS}, author={Wu, F. and Zheng, J. K. and Cai, W. and Yao, N. and Zhu, Y. T. and Narayan, J.}, year={2015}, month={Aug}, pages={238–243} }
 @article{singamaneni_prater_nori_kumar_lee_misra_narayan_2015, title={Ferroelectric and magnetic properties of multiferroic BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated with Si (100)}, volume={117}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4913811}, DOI={10.1063/1.4913811}, abstractNote={We report on the electrical, ferroelectric, and magnetic properties of BiFeO3 (BFO)-La0.7Sr0.3MnO3 heterostructures deposited epitaxially onto Si(100) substrates. Temperature dependent (200–350 K) current-voltage (I-V), switching spectroscopy piezo-response force microscopy (SSPFM), and temperature dependent (5–300 K) anisotropic magnetization measurements have been performed. The BFO (100-nm thick)-based device structures were fabricated with a 250 nm thick La0.7Sr0.3MnO3 bottom electrode and 200 μm circular top Pt electrodes. I-V measurements performed at various temperatures indicated that the devices retained their as-deposited characteristics and exhibited non-leaky behavior up to at least 50 cycles. The temperature-dependent measurements showed clear diode-like behavior and resistive (hysteretic) switching behaviour. Characteristic butterfly loops (of several cycles) were observed in the PFM amplitude signals of the BFO film. In addition, the phase signal indicated a clear (180°) switching behavior at the switching voltage of 4–5 V, providing unambiguous evidence for the occurrence of ferroelectricity in BFO films integrated on Si (100). The temperature- and angle-dependent zero field cooled isothermal (5 K) magnetization measurements were consistent with the presence of uniaxial magnetic anisotropy. This work makes an important step for the fabrication of CMOS-compatible BFO devices for memory applications.}, number={17}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Prater, J. T. and Nori, S. and Kumar, D. and Lee, Bongmook and Misra, V. and Narayan, J.}, year={2015}, month={May}, pages={17D908} }
 @misc{singamaneni_prater_narayan_2015, title={Magnetic exchange coupling in bilayers of two epitaxial ferromagnetic oxides}, volume={19}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2015.03.002}, abstractNote={Despite a decade of research effort on La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) bilayers (BLs), a full knowledge on the magnetic properties and integration of these BLs on silicon substrate is not yet in sight. In this paper, we report on the magnetic exchange coupling observed from the above two ferromagnetic oxide thin film BLs, prepared through a novel approach, called ‘domain matching epitaxy’. LSMO (100 nm)/SRO (45 nm) and LSMO (31 nm)/SRO (45 nm) bilayers have been epitaxially integrated with Si (1 0 0). Notably, in the former sample, positive exchange bias is observed – an indication of antiferromagnetic exchange coupling and is found to be absent in the latter. Furthermore, in the former sample, the cross-over from antiferromagnetic to ferromagnetic interface exchange coupling is noticed by varying the cooling field. We have verified that this coupling is of magnetic origin, not due to electrostatic interaction by inserting a thin (∼10 nm) SrTiO3 layer between LSMO and SRO. We believe that in addition to the formation of interface domain walls, the strong interplay among Zeeman, anisotropic and exchange energies could play a dominant role. Our results would have important implications for devices comprising of magnetic exchange coupled systems.}, number={5}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Singamaneni, Srinivasa Rao and Prater, John T. and Narayan, Jagdish}, year={2015}, month={Oct}, pages={301–304} }
 @article{lee_kumar_hunte_narayan_schwartz_2015, title={Microstructure and transport properties of epitaxial topological insulator Bi2Se3 thin films grown on MgO (100), Cr2O3 (0001), and Al2O3 (0001) templates}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4932027}, DOI={10.1063/1.4932027}, abstractNote={We report the epitaxial integration of defect-induced room temperature ferromagnetic insulators, Cr2O3 and MgO, with topological insulators Bi2Se3 on c-sapphire substrate by pulsed laser deposition. The structural, magnetic, and magnetotransport properties of ∼15 nm Bi2Se3 thin films are investigated on each template. The lattice misfits of Cr2O3/Bi2Se3 and MgO/Bi2Se3 are ∼16% and ∼39%, respectively, where the critical thickness for pseudomorphic growth is less than one monolayer. The insulating behavior is more pronounced due to the additional scattering of the surface states of the Bi2Se3 layer by interfacing with MgO and Cr2O3. The weak antilocalization effect from the surface states is clearly suppressed, accounting for the presence of magnetic bottom layers. This work demonstrates an effective way to study the emergence of a ferromagnetic phase in topological insulators by the magnetic proximity effect in Bi2Se3, a step toward unveiling their exotic properties.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Lee, Y. F. and Kumar, R. and Hunte, F. and Narayan, J. and Schwartz, J.}, year={2015}, month={Sep}, pages={125309} }
 @misc{singamaneni_narayan_prater_2015, title={Multifunctional heterostructures integrated on Si (100)}, volume={4}, number={1}, journal={Emerging Materials Research}, author={Singamaneni, S. R. and Narayan, J. and Prater, J. T.}, year={2015}, pages={50–70} }
 @article{narayan_bhaumik_2015, title={Novel phase of carbon, ferromagnetism, and conversion into diamond}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4936595}, DOI={10.1063/1.4936595}, abstractNote={We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp3 (75%–85%) with the rest being threefold sp2 bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g−1. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond formation.}, number={21}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2015}, month={Dec}, pages={215303} }
 @article{narayan_bhaumik_2015, title={Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air}, volume={3}, ISSN={2166-532X}, url={http://dx.doi.org/10.1063/1.4932622}, DOI={10.1063/1.4932622}, abstractNote={We report on fundamental discovery of conversion of amorphous carbon into diamond by irradiating amorphous carbon films with nanosecond lasers at room-temperature in air at atmospheric pressure. We can create diamond in the form of nanodiamond (size range <100 nm) and microdiamond (>100 nm). Nanosecond laser pulses are used to melt amorphous diamondlike carbon and create a highly undercooled state, from which various forms of diamond can be formed upon cooling. The quenching from the super undercooled state results in nucleation of nanodiamond. It is found that microdiamonds grow out of highly undercooled state of carbon, with nanodiamond acting as seed crystals.}, number={10}, journal={APL Materials}, publisher={AIP Publishing}, author={Narayan, Jagdish and Bhaumik, Anagh}, year={2015}, month={Oct}, pages={100702} }
 @article{punugupati_narayan_hunte_2015, title={Room temperature ferromagnetism in epitaxial Cr2O3 thin films grown on r-sapphire}, volume={117}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4921435}, DOI={10.1063/1.4921435}, abstractNote={We report on the epitaxial growth and magnetic properties of Cr2O3 thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011¯2) of Cr2O3 grows on r-plane of sapphire. The epitaxial relations can be written as [011¯2] Cr2O3 ‖ [011¯2] Al2O3 (out-of-plane) and [1¯1¯20] Cr2O3 ‖ [1¯1¯20] Al2O3 (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr2O3 thin films is due to the strain caused by defects, such as oxygen vacancies.}, number={19}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Punugupati, Sandhyarani and Narayan, Jagdish and Hunte, Frank}, year={2015}, month={May}, pages={193907} }
 @article{ma_zhou_narayan_zhu_2015, title={Stacking-fault energy effect on zero-strain deformation twinning in nanocrystalline Cu-Zn alloys}, volume={109}, ISSN={["1359-6462"]}, DOI={10.1016/j.scriptamat.2015.07.027}, abstractNote={It has been reported that most deformation twins in nanocrystalline face-centered-cubic metals do not produce macroscopic strain. Here we report the decrease of zero-strain deformation twinning with decreasing stacking-fault energy. One of the two major mechanisms that produce zero-strain twinning is cooperative slip of three partials under external applied stress. Lower stacking-fault energy weakens this mechanism and statistically reduces the fraction of twins with zero-strain.}, journal={SCRIPTA MATERIALIA}, author={Ma, X. L. and Zhou, H. and Narayan, J. and Zhu, Y. T.}, year={2015}, month={Dec}, pages={89–93} }
 @article{jin_nori_lee_kumar_wu_prater_kim_narayan_2015, title={Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4934498}, DOI={10.1063/1.4934498}, abstractNote={We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.}, number={16}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Jin, Zhenghe and Nori, Sudhakar and Lee, Yi-Fang and Kumar, D. and Wu, Fan and Prater, J. T. and Kim, Ki Wook and Narayan, Jagdish}, year={2015}, month={Oct}, pages={165309} }
 @article{molaei_bayati_wu_narayan_2014, title={A microstructural approach toward the effect of thickness on semiconductor-to-metal transition characteristics of VO2 epilayers}, volume={115}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4872030}, DOI={10.1063/1.4872030}, abstractNote={We report the control of semiconductor to metal transition in VO2(010) epilayers integrated with Si{100} substrates buffered with an NiO[111]/YSZ[100] intermediate layer. VO2 epitaxial thin films were grown at different thicknesses varying from 10 to 200 nm using pulsed laser deposition technique. An epitaxial relationship of VO2(010)‖NiO(111)‖ YSZ(001)‖Si(001) and VO2[100]‖NiO[110]‖ YSZ[100]‖Si[100] was established at room temperature. The crystallographic alignment across the VO2/NiO interface changes to VO2(100)‖NiO(111) and VO2[001]‖NiO[110] at the temperature of growth giving rise to a misfit strain of about 33.5% and 3.0% along two orthogonal in-plane orientations. The transition temperature was observed to vary from about 353 to 341 K, the transition amplitude increased by about five orders of magnitude, and the hysteresis decreased to about 3 K, as the thickness of VO2 layers increased from about 10 to 200 nm. These observations were explained based on strain characteristics, overall defect content and grain boundaries, and phenomenological thermodynamic models.}, number={16}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Molaei, R. and Bayati, R. and Wu, F. and Narayan, J.}, year={2014}, month={Apr}, pages={164311} }
 @article{gbordzoe_kotoka_craven_kumar_wu_narayan_2014, title={Effect of substrate temperature on the microstructural properties of titanium nitride nanowires grown by pulsed laser deposition}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4893298}, DOI={10.1063/1.4893298}, abstractNote={The current work reports on the growth and microstructural characterization of titanium nitride (TiN) nanowires on single crystal silicon substrates using a pulsed laser deposition method. The physical and microstructural properties of the nanowires were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The corrosion properties of the TiN nanowires compared to TiN thin film were evaluated using Direct Current potentiodynamic and electrochemical impedance spectroscopy. The nanowires corroded faster than the TiN thin film, because the nanowires have a larger surface area which makes them more reactive in a corrosive environment. It was observed from the FESEM image analyses that as the substrate temperature increases from 600 °C to 800 °C, there was an increase in both diameter (25 nm–50 nm) and length (150 nm–250 nm) of the nanowire growth. There was also an increase in spatial density with an increase of substrate temperature. The TEM results showed that the TiN nanowires grow epitaxially with the silicon substrate via domain matching epitaxy paradigm, despite a large misfit.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Gbordzoe, S. and Kotoka, R. and Craven, Eric and Kumar, D. and Wu, F. and Narayan, J.}, year={2014}, month={Aug}, pages={064310} }
 @misc{lee_punugupati_wu_jin_narayan_schwartz_2014, title={Evidence for topological surface states in epitaxial Bi2Se3 thin film grown by pulsed laser deposition through magneto-transport measurements}, volume={18}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2014.07.001}, abstractNote={We report epitaxial growth via domain matching epitaxy of Bi2Se3 thin films on Al2O3 (0 0 0 1) substrates with over 13% lattice misfit and critical thickness less than one monolayer. X-ray and electron diffraction patterns confirm that the layers are epitaxial with (0 0 0 1) Bi2Se3 || (0 0 0 1) Al2O3 and [21¯1¯0] Bi2Se3 || [21¯1¯0] Al2O3 (or) [21¯1¯0] Bi2Se3 || [112¯0] Al2O3 without the presence of an interfacial pseudomorphic layer. X-ray photoemission spectroscopy reveals that the films are Se-deficient, in agreement with electrical transport data showing n-type carriers and metallic behavior. Magneto-resistance (MR) measurements show a cusp feature corresponding to weak antilocalization and linear-MR shows a non-saturating trend up to 9 T. These results suggest topological surface states in PLD-grown Bi2Se3 films.}, number={5}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Lee, Y. F. and Punugupati, S. and Wu, F. and Jin, Z. and Narayan, J. and Schwartz, J.}, year={2014}, month={Oct}, pages={279–285} }
 @article{singamaneni_punugupati_prater_hunte_narayan_2014, title={Ferroelectric and ferromagnetic properties in BaTiO3thin films on Si (100)}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4894508}, DOI={10.1063/1.4894508}, abstractNote={In this paper, we report on the epitaxial integration of room temperature lead-free ferroelectric BaTiO3 thin (∼1050 nm) films on Si (100) substrates by pulsed laser deposition technique through a domain matching epitaxy paradigm. We employed MgO and TiN as buffer layers to create BaTiO3/SrRuO3/MgO/TiN/Si (100) heterostructures. C-axis oriented and cube-on-cube epitaxial BaTiO3 is formed on Si (100) as evidenced by the in-plane and out-of-plane x-ray diffraction, and transmission electron microscopy. X-ray photoemission spectroscopic measurements show that Ti is in 4(+) state. Polarization hysteresis measurements together with Raman spectroscopy and temperature-dependent x-ray diffraction confirm the room temperature ferroelectric nature of BaTiO3. Furthermore, laser irradiation of BaTiO3 thin film is found to induce ferromagnetic-like behavior but affects adversely the ferroelectric characteristics. Laser irradiation induced ferromagnetic properties seem to originate from the creation of oxygen vacancies, whereas the pristine BaTiO3 shows diamagnetic behavior, as expected. This work has opened up the route for the integration of room temperature lead-free ferroelectric functional oxides on a silicon platform.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Punugupati, Sandhyarani and Prater, John T. and Hunte, Frank and Narayan, Jagdish}, year={2014}, month={Sep}, pages={094103} }
 @article{temizer_nori_narayan_2014, title={Ga and Al doped zinc oxide thin films for transparent conducting oxide applications: Structure-property correlations}, volume={115}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4861420}, DOI={10.1063/1.4861420}, abstractNote={We report a detailed investigation on the structure-property correlations in Ga and Al codoped ZnO films on c-sapphire substrates where the thin film microstructure varies from nanocrystalline to single crystal. We have achieved highly epitaxial films with very high optical transmittance (close to 90%) and low resistivity (∼110 μΩ-cm) values. The films grown in an ambient oxygen partial pressure (PO2) of 5 × 10−2 Torr and at growth temperatures from room temperature to 600 °C show semiconducting behavior, whereas samples grown at a PO2 of 1 × 10−3 Torr show metallic nature. The most striking feature is the occurrence of resistivity minima at relatively high temperatures around 110 K in films deposited at high temperatures. The measured optical and transport properties were found to be a strong function of growth conditions implying that the drastic changes are brought about essentially by native point defects. The structure-property correlations reveal that point defects play an important role in modifying the structural, optical, electrical, and magnetic properties and such changes in physical properties are controlled predominantly by the defect content.}, number={2}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Temizer, Namik K. and Nori, Sudhakar and Narayan, Jagdish}, year={2014}, month={Jan}, pages={023705} }
 @article{gupta_narayan_2014, title={Integration and structural analysis of strain relaxed bi-epitaxial zinc oxide(0001) thin film with silicon(100) using titanium nitride buffer layer}, volume={115}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4861638}, DOI={10.1063/1.4861638}, abstractNote={Epitaxial growth of c-plane ZnO(0001) has been demonstrated on the Si(001) by using TiN as an intermediate buffer layer. Because of different out of plane symmetry of the substrate (Si/TiN) and the film (ZnO), two orientations of ZnO domains were obtained and the ZnO film growth is of bi-epitaxial nature. The ZnO thin film was observed to be nearly strain relaxed from X-ray and Raman measurements. The interface between the ZnO and TiN was investigated by transmission electron microscopy, and atomic arrangement has been modeled to understand the crystallographic orientation and structure of the domain/grain boundaries. Reaction at ZnO/TiN interface at higher growth temperature causing zinc titanate formation was observed. The grain boundary structure between the observed domains investigated by scanning transmission electron microscopy, revealed the ZnO(0001) planes to be contiguous across the grain boundary which is significant from the perspective of conduction electron scattering. In this configuration, the TiN (being electrically conductive) can be effectively used as an electrode for novel vertically integrated device applications (like light emitting diodes) directly on Si(100) substrate.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Gupta, Pranav and Narayan, Jagdish}, year={2014}, month={Jan}, pages={043513} }
 @article{rao_lee_prater_smirnov_narayan_2014, title={Laser annealing induced ferromagnetism in SrTiO3 single crystal}, volume={105}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4891184}, DOI={10.1063/1.4891184}, abstractNote={The appearance of ferromagnetic order up to 400 K upon KrF (248 nm) laser irradiation is reported in un-doped SrTiO3 (STO) single crystal. The high resolution x-ray photo emission spectroscopy (XPS) measurements reveal a strong shift of Sr-, Ti-, and O-related peaks. X-ray diffraction of laser annealed STO does not reveal a signature of either secondary magnetic or amorphous phases. 300 K X-band (∼9.543 GHz) angle-dependent electron paramagnetic resonance (EPR) measurements showed no evidence of additional magnetic peaks upon laser irradiation. XPS and EPR data did not provide a strong evidence of Ti3+ formation upon laser annealing. No differences in the visible 300 K Raman spectra of pristine and laser annealed STO are noticed. Interestingly, the magnetic moment is decreased by almost 10-fold upon oxygen annealing of laser annealed STO, inferring that oxygen vacancies play an important role in establishing the observed ferromagnetism.}, number={4}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Rao, S. S. and Lee, Y. F. and Prater, J. T. and Smirnov, A. I. and Narayan, J.}, year={2014}, month={Jul}, pages={042403} }
 @article{singamaneni_fan_prater_narayan_2014, title={Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4903322}, DOI={10.1063/1.4903322}, abstractNote={Two-phase multiferroic heterostructures composed of room-temperature ferroelectric BaTiO3 (BTO) and ferromagnetic La0.7Sr0.3MnO3 (LSMO) epitaxial thin films were grown on technologically important substrate Si (100). Bilayers of BTO/LSMO thin films display ferromagnetic Curie transition temperatures of ∼350 K, close to the bulk value, which are independent of BTO films thickness in the range of 25–100 nm. Discontinuous magnetization jumps associated with BTO structural transitions were suppressed in M(T) curves, probably due to substrate clamping effect. Interestingly, at cryogenic temperatures, the BTO/LSMO structure with BTO layer thickness of 100 nm shows almost 2-fold higher magnetic coercive field, 3-fold reduction in saturation magnetization, and improved squareness compared to the sample without BTO. We believe that the strong in-plane spin pinning of the ferromagnetic layer induced by BTO layer at BTO/LSMO interface could cause such changes in magnetic properties. This work forms a significant step forward in the integration of two-phase multiferroic heterostructures for CMOS applications.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Singamaneni, Srinivasa Rao and Fan, Wu and Prater, J. T. and Narayan, J.}, year={2014}, month={Dec}, pages={224104} }
 @article{bayati_molaeil_richmond_nori_wu_kumar_narayan_reynolds_reynolds_2014, title={Modification of Properties of Yttria Stabilized Zirconia Epitaxial Thin Films by Excimer Laser Annealing}, volume={6}, ISSN={["1944-8252"]}, DOI={10.1021/am506298y}, abstractNote={This study focuses on the ultrafast improvement of surface wettability, electrical, and room temperature magnetic characteristics of cubic zirconia single crystalline thin films after laser annealing. The point defects generated by the laser treatment are envisaged to play a critical role in altering the above properties. Yttria stabilized zirconia (YSZ) thin films were epitaxially grown on Si(100) substrates by pulsed laser deposition technique and subsequently annealed by a KrF excimer laser beam (τ = 25 ns) using low-energy laser pulses. An atomically sharp interface, parallel to the film free surface, between laser annealed layer and the pristine region was observed. The single crystalline nature of thin films was preserved following the laser treatment. The laser-solid interaction with YSZ led to the introduction of point defects, i.e., oxygen vacancies, resulting in a strained structure which, in turn, resulted in the formation of a tetragonal-like zirconia. With the increase of number of laser pulses the laser treated films got highly disordered due to the high concentration of the point defects, while maintaining their crystalline nature. Although the surface of the pristine sample showed weak hydrophilic characteristics (contact angle ∼ 73°), the laser annealed samples exhibited significantly improved hydrophilic characteristics. It was found that there is an optimum number of laser pulses where the maximum hydrophilicity (contact angle ∼ 22°) is obtained. The carrier concentration in the sample with the highest hydrophilicity was determined to be higher by about 5 orders of magnitude compared to the pristine sample. This sample possessed the lowest electrical resistivity. The laser annealed YSZ epilayers showed a superior room-temperature ferromagnetic behavior, compared to the pristine samples. A 2-fold enhancement in the magnetization of the samples was observed following the laser treatment which is a clear demonstration of the key role of defects and their transient distribution throughout the lattice. All these observations were correlated with the formation of point defects due to the photon interaction with YSZ and absorption of energy of the KrF laser photons to produce defects.}, number={24}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Bayati, R. and Molaeil, R. and Richmond, A. and Nori, S. and Wu, F. and Kumar, D. and Narayan, J. and Reynolds, J. G. and Reynolds, C. L., Jr.}, year={2014}, month={Dec}, pages={22316–22325} }
 @article{bayati_molaei_richmond_narayan_nori_wu_kumar_reynolds_reynold jr._2014, title={Modification of properties of yttria stabilized zirconia epitaxial thin films}, volume={6}, number={24}, journal={ACS Applied Materials and Interfaces}, author={Bayati, R. and Molaei, R. and Richmond, A. and Narayan, J. and Nori, S. and Wu, F. and Kumar, Dhananjay and Reynolds, J.G. and Reynold Jr., C.L.}, year={2014}, month={Apr}, pages={22316–22325} }
 @article{lee_wu_narayan_schwartz_2014, title={Oxygen vacancy enhanced room-temperature ferromagnetism in Sr3SnO/c-YSZ/Si (001) heterostructures}, volume={4}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2014.4}, abstractNote={The magnetic properties of Sr_3SnO (SSO) epitaxial thin films prepared under various post-growth annealing treatments are reported. The SSO films are grown on cubic yttria-stabilized zirconia Si (001) platform by pulsed laser deposition. Post-growth vacuum annealing is found to enhance the room-temperature ferromagnetism (RTFM), whereas oxygen annealing reduces it. The results are explained through the oxygen vacancy constituted bound magnetic polarons (BMP) model. An empirical relationship between the extracted BMP concentration and the oxygen vacancy concentration is shown using X-ray photoelectron spectroscopy data. The results indicate a promising way to tune RTFM by manipulating oxygen vacancies and related defects.}, number={1}, journal={MRS COMMUNICATIONS}, author={Lee, Y. F. and Wu, F. and Narayan, J. and Schwartz, J.}, year={2014}, month={Apr}, pages={7–13} }
 @article{rao_prater_wu_nori_kumar_yue_liou_narayan_2014, title={Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)}, volume={18}, ISSN={1359-0286}, url={http://dx.doi.org/10.1016/J.COSSMS.2014.02.001}, DOI={10.1016/J.COSSMS.2014.02.001}, abstractNote={In magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni82.5Fe17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0).}, number={3}, journal={Current Opinion in Solid State and Materials Science}, publisher={Elsevier BV}, author={Rao, S.S. and Prater, J.T. and Wu, Fan and Nori, S. and Kumar, D. and Yue, L. and Liou, S.-H. and Narayan, J.}, year={2014}, month={Jun}, pages={140–146} }
 @article{punugupati_narayan_hunte_2014, title={Strain induced ferromagnetism in epitaxial Cr2O3 thin films integrated on Si(001)}, volume={105}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4896975}, DOI={10.1063/1.4896975}, abstractNote={We report on the epitaxial growth and magnetic properties of antiferromagnetic and magnetoelectric (ME) Cr2O3 thin films deposited on cubic yttria stabilized zirconia (c-YSZ)/Si(001) using pulsed laser deposition. The X-ray diffraction (2ϴ and Φ) and TEM characterizations confirm that the films were grown epitaxially. The Cr2O3(0001) growth on YSZ(001) occurs with twin domains. There are four domains of Cr2O3 with in-plane rotation of 30° or 150° from each other about the [0001] growth direction. The epitaxial relation between the layers is given as [001]Si ‖ [001]YSZ ‖ [0001]Cr2O3 and [100]Si ǁ [100]YSZ ǁ [101¯0] Cr2O3 or [112¯0] Cr2O3. Though the bulk Cr2O3 is an antiferromagnetic with TN = 307 K, we found that the films exhibit ferromagnetic like hysteresis loops with high saturation and finite coercive field up to 400 K. The thickness dependent magnetizations together with oxygen annealing results suggest that the ferromagnetism (FM) is due to oxygen related defects whose concentration is controlled by strain present in the films. This FM, in addition to the intrinsic magneto-electric properties of Cr2O3, opens the door to relevant spintronics applications.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Punugupati, Sandhyarani and Narayan, Jagdish and Hunte, Frank}, year={2014}, month={Sep}, pages={132401} }
 @article{punugupati_temizer_narayan_hunte_2014, title={Structural and resistance switching properties of epitaxial Pt/ZnO/TiN/Si(001) heterostructures}, volume={115}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4883959}, DOI={10.1063/1.4883959}, abstractNote={We report the bi-epitaxial growth of ZnO and resistance switching characteristics of Pt/ZnO/TiN-based heterojunction devices fabricated on Si(001) substrates by pulsed laser deposition. The structural properties of the heterostructures characterized by XRD (θ-2θ, φ scans) and TEM confirm that the ZnO films having hexagonal wurtzite structure (six-fold symmetry) grow bi-epitaxially on the TiN buffer layer (four-fold symmetry). The Pt(111) grows epitaxially on ZnO(0001). The epitaxial relationship between the various films is given as (111)Pt ‖ (0001)ZnO ‖ (001)TiN ‖ (001)Si and [100]TiN ‖ [100]Si, [21¯1¯0]ZnO ‖ [110]TiN or [101¯0]ZnO ‖ [110]TiN, and [101¯]Pt ‖ [21¯1¯0]ZnO. The effect of ZnO growth temperature on the electrical properties of Pt/ZnO/TiN devices is studied and correlated with the microstructure of the ZnO/TiN interface. The Pt/ZnO/TiN devices exhibited good bi-polar resistance switching characteristics at voltages as low as ±1 V.}, number={23}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Punugupati, Sandhyarani and Temizer, Namik K. and Narayan, Jagdish and Hunte, Frank}, year={2014}, month={Jun}, pages={234501} }
 @article{bharathan_zhou_narayan_rozgonyi_bulman_2014, title={Thermal Misfit Strain Relaxation in Ge/(001)Si Heterostructures}, volume={43}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-014-3247-6}, number={9}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bharathan, Jayesh and Zhou, Honghui and Narayan, Jagdish and Rozgonyi, George and Bulman, Gary E.}, year={2014}, month={Sep}, pages={3196–3203} }
 @article{lee_narayan_schwartz_2014, title={Tunable electronic structure in dilute magnetic semiconductor Sr3SnO/c-YSZ/Si (001) epitaxial heterostructures}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4899438}, DOI={10.1063/1.4899438}, abstractNote={We report a systematic study of the structural, physical, and chemical properties of epitaxial thin films of emerging dilute magnetic semiconductor (DMS) Sr3SnO (SSO) integrated with Si (100) prepared by various post-growth annealing treatments. The transport properties of these films are primarily governed by oxygen vacancies and the results are explained with the variable-range hopping model. The increased oxygen vacancy concentration generated by post-growth vacuum annealing results in a shorter hopping distance and reduced hopping energy and Coulomb gap, leading to lower resistivity; oxygen annealing shows the opposite effects. The work function ranges from 4.54 to 4.02 eV and shows a negative linear relationship with oxygen vacancy concentration, accompanied by a 0.42 eV shift in the surface Fermi level. The transport and ultraviolet photoelectron spectroscopy probes agree quantitatively on measurement of the resistivity and surface electronic structure. The results provide a direct and consistent explanation that the property changes in the bulk and at the surface are primarily attributed to oxygen vacancies, which are believed to be the carriers in the SSO thin films. The ability to manipulate the work function and oxygen vacancy concentration in epitaxial DMS SSO thin films offers great potential for the development of spintronic devices.}, number={16}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Lee, Y. F. and Narayan, J. and Schwartz, J.}, year={2014}, month={Oct}, pages={164903} }
 @misc{wu_rao_prater_zhu_narayan_2014, title={Tuning exchange bias in epitaxial Ni/MgO/TiN heterostructures integrated on Si(100)}, volume={18}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2014.09.002}, abstractNote={Epitaxial Ni thin films are integrated with tunneling barrier MgO on Si(1 0 0) substrate. During pulsed laser deposition, early island-like structure transformed into uniform thin film with increasing number of laser pulses. This led to transitions in exchange bias from positive to negative and back to positive, which is ascribed to morphology associated residual strain. The Ni island structure has a coercive field as high as 3 times of that of the continuous film. The current work holds a tremendous promise in the realization of magnetic devices integrated with the Si-platform.}, number={5}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Wu, F. and Rao, S. S. and Prater, J. T. and Zhu, Y. T. and Narayan, J.}, year={2014}, month={Oct}, pages={263–268} }
 @misc{zhou_chisholm_gupta_pennycook_narayan_2014, title={Two-dimensional metamaterials for epitaxial heterostructures}, volume={18}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2014.01.001}, abstractNote={We review the use of two-dimensional psuedomorphic materials to accommodate an extraordinary range of misfit and allow novel new phases to be grown epitaxially. These materials assume the structure of the substrate and can thus be regarded as metamaterials. We illustrate these principles through a number of systems, including a detailed structural and spectroscopic study of epitaxial VO2/NiO heterostructures. In this case the metamaterial is VO1+x which is structurally and electronically distinct from the bulk of the VO2 film. In the transition region the crystal structure adopts that of the NiO layer, while the oxidation state of vanadium increases from ∼3+ to ∼4+ with thickness, accompanied by increasing lattice disorder. The formation and evolution of this interfacial phase, VO1+x, accommodates the change in crystal symmetry across the interface from the rock-salt structure of NiO to the rutile structure of VO2. The use of two-dimensional metamaterials opens a wealth of new opportunities for the growth of new materials with novel properties.}, number={1}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Zhou, H. and Chisholm, M. F. and Gupta, A. and Pennycook, S. J. and Narayan, J.}, year={2014}, month={Feb}, pages={46–52} }
 @article{narayan_2013, title={A new mechanism for field-assisted processing and flash sintering of materials}, volume={69}, DOI={10.1016/j.scriptamat.2013.02.020}, abstractNote={A unified mechanism for field-assisted phenomena such as enhanced rapid flash sintering, reduction in flow stress and grain growth retardation is proposed. It is argued that defect segregation causes enhanced ionic and electronic transport along dislocations and grain boundaries, which leads to enhanced mobility of dislocations and their selective Joule heating. This selective heating, if uncontrolled, can lead to an avalanche and selective melting of grain boundaries, which is proposed to be the primary mechanism for flash sintering of oxides.}, number={2}, journal={Scripta Materialia}, author={Narayan, Jagdish}, year={2013}, pages={107–111} }
 @article{wu_narayan_2013, title={Controlled Epitaxial Growth of Body-Centered Cubic and Face-Centered Cubic Cu on MgO for Integration on Si}, volume={13}, ISSN={["1528-7505"]}, DOI={10.1021/cg4011983}, abstractNote={The Cu/MgO interface plays a crucial role in applications. Face-centered-cubic (fcc) Cu has been reported to grow on MgO substrate (rock salt structure). However, no body-centered-cubic/tetragonal (bcc(t)) Cu has been stabilized on MgO. The special atomic structure of the bcc(t)/rock salt interface contributes to superior thermal, mechanical, and electrical properties. We report, for the first time, the epitaxial growth of bcc(t) and fcc Cu on Si(100) and Si(111) substrates using MgO(100)/TiN(100) and MgO(111)/TiN(111) buffer layers by pulsed laser deposition. We find that the deposition temperature determines the structure of Cu. At high temperature, only fcc Cu grows on both MgO/TiN(100) and MgO/ TiN(111) templates. At room temperature, an epitaxial layer of bcc(t) Cu grows pseudomorphically on a MgO(100) template up to the critical thickness, while on a MgO/TiN(111) template, the majority of Cu is fcc, and bcc(t) Cu exists occasionally in a three-dimensional island shape. The growth of these heterostructures involves epitaxy across the misfit scale by matching MgO{200} planes with bcc(t) Cu{110} planes. The integration of Cu/MgO on the technologically important Si substrate holds tremendous promise, because the novel bcc(t) Cu/MgO structure can be integrated with present-day microelectronic or nanoelectronic devices.}, number={11}, journal={CRYSTAL GROWTH & DESIGN}, author={Wu, F. and Narayan, J.}, year={2013}, month={Nov}, pages={5018–5024} }
 @article{molaei_bayati_alipour_narayan_2013, title={Controlled epitaxial integration of polar ZnO(0001) with Si(001)}, volume={102}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4795126}, DOI={10.1063/1.4795126}, abstractNote={We have grown ZnO(0001) single-crystalline thin films on Si(001) using cubic yttria-stabilized-zirconia (c-YSZ) buffer and analyzed details of epitaxy, twins, and interfaces. In-plane epitaxial relationship between ZnO and c-YSZ showed an interesting dependence on growth temperature where it changed from (0001)[2¯110]ZnO||(001)[110]c-YSZ to (0001)[2¯110]ZnO||(001)[100]c-YSZ as the temperature increased from 500 to 750 °C. At temperatures in between, a combination of these epitaxial relationships was observed. We found that the epitaxial relationships are determined by the surface termination characteristics of c-YSZ across the ZnO/c-YSZ interface. The crystallographic characteristics of c-ZnO/c-YSZ/Si(001) heterostructures can be precisely tuned to address the needs of next-generation solid-state devices.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Molaei, R. and Bayati, M. R. and Alipour, H. M. and Narayan, J.}, year={2013}, month={Mar}, pages={101602} }
 @article{bayati_molaei_wu_budai_liu_narayan_narayan_2013, title={Correlation between structure and semiconductor-to-metal transition characteristics of VO2/TiO2/sapphire thin film heterostructures}, volume={61}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2013.09.019}, abstractNote={This study focuses on the role of strain and thin film epitaxy on the semiconductor-to-metal transition (SMT) characteristics of single crystalline VO2 thin films. The VO2/TiO2 heterostructures of controlled orientations were epitaxially grown on m-cut, r-cut and c-cut sapphire substrates. Detailed structural investigations were performed using high-resolution X-ray diffraction (2θ–θ and φ scans) and high-resolution transmission electron microscopy techniques to correlate SMT properties with microstructural characteristics. Monoclinic (M1) VO2 thin films with (1 0 0), (0 0 1) and (2¯01) out-of-plane orientations were grown on TiO2(1 0 1)/r-sapphire, TiO2(1 0 0)/c-sapphire and TiO2(0 0 1)/m-sapphire platforms, respectively. The in-plane alignments across the interfaces were established to be [0 1 0](1 0 0)VO2||[0 1 0](1 0 1)TiO2, [1 0 0](0 0 1)VO2||[0 0 1](1 0 0)TiO2 and [010](2¯01)VO2‖[010](001)TiO2 for r-sapphire, c-sapphire and m-sapphire substrates, respectively. We were able to tune the SMT temperature of VO2 epilayers from ∼313 K to 354 K (bulk Tc ≈ 340 K). The SMT characteristics were interpreted based upon the residual strain in the VO2 lattice, particularly along the c-axis of tetragonal VO2. This research introduces the VO2-based single crystalline heterostructures as a potential candidate for a wide range of applications where different transition temperatures are required.}, number={20}, journal={ACTA MATERIALIA}, author={Bayati, M. R. and Molaei, R. and Wu, F. and Budai, J. D. and Liu, Y. and Narayan, R. J. and Narayan, J.}, year={2013}, month={Dec}, pages={7805–7815} }
 @article{molaei_bayati_narayan_2013, title={Crystallographic characteristics and p-Type to n-Type transition in epitaxial NiO thin film}, volume={13}, DOI={10.1021/cg401408f}, abstractNote={We were able to systematically control crystallographic characteristics and electrical properties of nickel oxide epitaxial thin films integrated with cubic yttria-stabilized zirconia (c-YSZ)-buffered silicon(001) substrates. The NiO epilayers were grown under several oxygen partial pressures by pulsed laser deposition. The out-of-plane orientation of the NiO layers showed an interesting behavior where it changed from ⟨111⟩ at lower pressures (7 × 10–6 Torr) to ⟨100⟩ at higher pressures (5 × 10–2 Torr). This observation was attributed to the nature of surface termination and templating effect of the c-YSZ{100} platform at different pressures. With the use of θ–2θ and φ scans of X-ray diffraction, the epitaxial alignment across the NiO/c-YSZ interface was determined to be {111}NiO|||{100}c-YSZ and ⟨110⟩NiO||⟨100⟩c-YSZ for the heterostructure grown under a low pressure and {100}NiO||{100}c-YSZ and ⟨100⟩NiO||⟨100⟩c-YSZ for the heterostructure grown under a high oxygen pressure. Our high-resolution TEM studie...}, number={12}, journal={Crystal Growth and Design}, author={Molaei, R. and Bayati, R. and Narayan, Jagdish}, year={2013}, pages={5459–5465} }
 @article{bharathan_narayan_rozgonyi_bulman_2013, title={Defect Characterization in Ge/(001)Si Epitaxial Films Grown by Reduced-Pressure Chemical Vapor Deposition}, volume={42}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-013-2686-9}, number={10}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bharathan, Jayesh and Narayan, Jagdish and Rozgonyi, George and Bulman, Gary E.}, year={2013}, month={Oct}, pages={2888–2896} }
 @article{gupta_singh_wu_narayan_mcmillen_alapatt_poole_hwu_sulejmanovic_young_et al._2013, title={Deposition and characterization of nanostructured Cu2O thin-film for potential photovoltaic applications}, volume={28}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2013.150}, abstractNote={Abstract}, number={13}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Gupta, Nishant and Singh, Rajendra and Wu, Fan and Narayan, Jagdish and McMillen, Colin and Alapatt, Githin F. and Poole, Kelvin F. and Hwu, Shiou-Jyh and Sulejmanovic, Dino and Young, Matthew and et al.}, year={2013}, month={Jul}, pages={1740–1746} }
 @article{molaei_bayati_nori_kumar_prater_narayan_2013, title={Diamagnetic to ferromagnetic switching in VO2 epitaxial thin films by nanosecond excimer laser treatment}, volume={103}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4857155}, DOI={10.1063/1.4857155}, abstractNote={VO2(010)/NiO(111) epitaxial heterostructures were integrated with Si(100) substrates using a cubic yttria-stabilized zirconia (c-YSZ) buffer. The epitaxial alignment across the interfaces was determined to be VO2(010)‖NiO(111)‖c-YSZ(001)‖Si(001) and VO2[100]‖NiO⟨110⟩‖c-YSZ⟨100⟩‖Si⟨100⟩. The samples were subsequently treated by a single shot of a nanosecond KrF excimer laser. Pristine as-deposited film showed diamagnetic behavior, while laser annealed sample exhibited ferromagnetic behavior. The population of majority charge carriers (e−) and electrical conductivity increased by about two orders of magnitude following laser annealing. These observations are attributed to the introduction of oxygen vacancies into the VO2 thin films and the formation of V3+ defects.}, number={25}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Molaei, R. and Bayati, R. and Nori, S. and Kumar, D. and Prater, J. T. and Narayan, J.}, year={2013}, month={Dec}, pages={252109} }
 @article{molaei_bayati_alipour_nori_narayan_2013, title={Enhanced photocatalytic efficiency in zirconia buffered n-NiO/p-NiO single crystalline heterostructures by nanosecond laser treatment}, volume={113}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4811540}, DOI={10.1063/1.4811540}, abstractNote={We report the formation of NiO based single crystalline p-n junctions with enhanced photocatalytic activity induced by pulsed laser irradiation. The NiO epilayers were grown on Si(001) substrates buffered with cubic yttria-stabilized zirconia (c-YSZ) by using pulsed laser deposition. The NiO/c-YSZ/Si heterostructures were subsequently laser treated by 5 pulses of KrF excimer laser (pulse duration = 25 × 10−9 s) at lower energies. Microstructural studies, conducted by X-ray diffraction (θ-2θ and φ techniques) and high resolution transmission electron microscope, showed a cube-on-cube epitaxial relationship at the c-YSZ/Si interface; the epitaxial relationship across the NiO/c-YSZ interface was established as NiO⟨111 ⟩||c-YSZ⟨001⟩ and in-plane NiO⟨110⟩||c-YSZ⟨100⟩. Electron microscopy studies showed that the interface between the laser annealed and the pristine region as well as the NiO/c-YSZ interface was atomically sharp and crystallographically continuous. The formation of point defects, namely oxygen vacancies and NiO, due to the coupling of the laser photons with the NiO epilayers was confirmed by XPS. The p-type electrical characteristics of the pristine NiO epilayers turned to an n-type behavior and the electrical conductivity was increased by one order of magnitude after laser treatment. Photocatalytic activity of the pristine (p-NiO/c-YSZ/Si) and the laser-annealed (n-NiO/p-NiO/c-YSZ/Si) heterostructures were assessed by measuring the decomposition rate of 4-chlorophenol under UV light. The photocatalytic reaction rate constants were determined to be 0.0059 and 0.0092 min−1 for the as-deposited and the laser-treated samples, respectively. The enhanced photocatalytic efficiency was attributed to the suppressed charge carrier recombination in the NiO based p-n junctions and higher electrical conductivity. Besides, the oxygen vacancies ease the adsorption of 4-chlorophenol, hydroxyl, and water molecules to the surface. Thus, n-NiO/p-NiO single crystalline catalysts can be introduced as a potent candidate to remediate the environmental pollution.}, number={23}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Molaei, R. and Bayati, M. R. and Alipour, H. M. and Nori, S. and Narayan, J.}, year={2013}, month={Jun}, pages={233708} }
 @article{lee_wu_kumar_hunte_schwartz_narayan_2013, title={Epitaxial integration of dilute magnetic semiconductor Sr3SnO with Si (001)}, volume={103}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4820770}, DOI={10.1063/1.4820770}, abstractNote={Epitaxial thin films heterostructures of topological insulator candidate Sr3SnO (SSO) are grown on a cubic yttria-stabilized zirconia (c-YSZ)/Si (001) platform by pulsed laser deposition. X-ray and electron diffraction patterns confirm the epitaxial nature of the layers with cube-on-cube orientation relationship: (001)[100]SSO∥(001)[100]c-YSZ∥(001)[100]Si. The temperature dependent electrical resistivity shows semiconductor behavior with a transport mechanism following the variable-range-hopping model. The SSO films show room-temperature ferromagnetism with a high saturation magnetization, and a finite non-zero coercivity persisting up to room temperature. These results indicate that SSO is a potential dilute magnetic semiconductor, presumably obtained by controlled introduction of intrinsic defects.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Lee, Y. F. and Wu, F. and Kumar, R. and Hunte, F. and Schwartz, J. and Narayan, J.}, year={2013}, month={Sep}, pages={112101} }
 @article{lee_wu_narayan_2013, title={Epitaxial integration of topological insulator SrSnO with c-YSZ/Si(001)}, volume={103}, journal={Applied Physics Letters}, author={Lee, Y. and Wu, F. and Narayan, J.}, year={2013} }
 @article{narayan_2013, title={Field-assisted selective-melt sintering: a novel approach to high-density ceramics}, volume={3}, ISSN={["2159-6867"]}, DOI={10.1557/mrc.2013.27}, abstractNote={Electrical fields can be used to heat selectively dislocations and grain boundaries to a much higher temperature compared with the bulk. This selective joule heating, if uncontrolled by limiting the current flow, can lead to melting of grain boundaries and sintering of poly- and nanocrystalline materials close to the theoretical density in a much shorter time due to fast diffusivities of the order of 10^−4 to 10^−5 cm^2/s in the liquid. I refer to this sintering mode as selective-melt sintering, which can occur at lower overall temperatures with much lower energy consumption compared with conventional sintering involving solid-state diffusion.}, number={3}, journal={MRS COMMUNICATIONS}, author={Narayan, J.}, year={2013}, month={Sep}, pages={139–143} }
 @article{narayan_schwartz_goyal_wang_jin_liao_2013, title={Frontiers in thin film epitaxy and nanostructured materials introduction}, volume={28}, number={13}, journal={Journal of Materials Research}, author={Narayan, J. and Schwartz, J. and Goyal, A. and Wang, H. Y. and Jin, S. H. and Liao, X. Z.}, year={2013}, pages={1625–1625} }
 @article{narayan_2013, title={Grain growth model for electric field-assisted processing and flash sintering of materials}, volume={68}, ISSN={["1359-6462"]}, DOI={10.1016/j.scriptamat.2013.01.008}, abstractNote={This paper proposes a model to explain interesting features of grain growth retardation and saturation during electric field-assisted processing and flash sintering of materials. It is argued that electric field-induced defect generation and segregation of these defects at dislocations and grain boundaries can retard the grain growth rate and reduce it to zero as a result of grain boundary melting under flash sintering. Grain growth rates are derived taking into account kinetic and various thermodynamic factors under an applied field and compared with other models.}, number={10}, journal={SCRIPTA MATERIALIA}, author={Narayan, J.}, year={2013}, month={May}, pages={785–788} }
 @article{zhu_liao_wu_narayan_2013, title={Grain size effect on deformation twinning and detwinning}, volume={48}, ISSN={["1573-4803"]}, DOI={10.1007/s10853-013-7140-0}, abstractNote={This article systematically overviews the grain size effect on deformation twinning and detwinning in face-centered cubic (fcc) metals. With decreasing grain size, coarse-grained fcc metals become more difficult to deform by twinning, whereas nanocrystalline (nc) fcc metals first become easier to deform by twinning and then become more difficult, exhibiting an optimum grain size for twinning. The transition in twinning behavior from coarse-grained to nc fcc metals is caused by the change in deformation mechanisms. An analytical model based on observed deformation physics in nc metals, i.e., grain boundary emission of dislocations, provides an explanation of the observed optimum grain size for twinning in nc fcc metals. The detwinning process is caused by the interaction between dislocations and twin boundaries. Under a certain deformation condition, there exists a grain size range where the twinning process dominates over the detwinning process to produce the highest density of twins.}, number={13}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Zhu, Y. T. and Liao, X. Z. and Wu, X. L. and Narayan, J.}, year={2013}, month={Jul}, pages={4467–4475} }
 @article{wu_zhu_narayan_2013, title={Grain size effect on twin density in as-deposited nanocrystalline Cu film}, volume={93}, ISSN={1478-6435 1478-6443}, url={http://dx.doi.org/10.1080/14786435.2013.829251}, DOI={10.1080/14786435.2013.829251}, abstractNote={Here, we report the formation of twins and grain size dependence of twin density in nanocrystalline (NC) copper films fabricated by pulsed laser deposition. It is found that the percentage of grains containing twins decreases with decreasing grain size in the grain size range of 2–10 nm. Surprisingly, although the twins were formed during the deposition process without mechanical deformation, our analysis suggests that they are most likely deformation twins formed under high internal stress existing in the NC Cu films. This phenomenon may also happen in other NC metallic thin films where internal stresses are high.}, number={35}, journal={Philosophical Magazine}, publisher={Informa UK Limited}, author={Wu, F. and Zhu, Y.T. and Narayan, J.}, year={2013}, month={Dec}, pages={4355–4363} }
 @article{budai_tselev_tischler_strelcov_kolmakov_liu_gupta_narayan_2013, title={In situ X-ray microdiffraction studies inside individual VO2 microcrystals}, volume={61}, ISSN={1359-6454}, url={http://dx.doi.org/10.1016/j.actamat.2012.09.074}, DOI={10.1016/j.actamat.2012.09.074}, abstractNote={Synchrotron X-ray microdiffraction provides quantitative structural measurements with submicron spatial resolution, and hence enables investigations of how local microstructural inhomogeneities affect materials’ properties. A combination of polychromatic and monochromatic X-ray microdiffraction was used to investigate domain formation, interface orientations and strain distributions inside individual vanadium dioxide (VO2) microcrystals. Using in situ measurements near the VO2 metal–insulator phase transition, it was found that the observed phase evolution is critically dependent on external strain. Substrate-induced strains or inhomogeneous sample heating can directly alter phase stability and affect the local domain orientations. In different clamped or freely suspended single-crystal samples, all the predicted twin laws for the M2 phase in VO2 were observed, except one. When the rutile and M2 phases coexist, it was found that different interphase boundary orientations can be stabilized by sample size and by interfacial elastic strain. The large variations in phase sequences and domain orientations observed in relatively simple, small single crystals provide insight into the mechanisms responsible for the broad structural and electronic transitions observed in epitaxial VO2 films.}, number={8}, journal={Acta Materialia}, publisher={Elsevier BV}, author={Budai, J.D. and Tselev, A. and Tischler, J.Z. and Strelcov, E. and Kolmakov, A. and Liu, W.J. and Gupta, A. and Narayan, J.}, year={2013}, month={May}, pages={2751–2762} }
 @misc{rao_prater_wu_nori_kumar_narayan_2014, title={Integration of epitaxial permalloy on Si (100) through domain matching epitaxy paradigm}, volume={18}, ISSN={["1879-0348"]}, DOI={10.1016/j.cossms.2013.07.004}, abstractNote={Abstract This paper addresses epitaxial integration of magnetic materials with Si (1 0 0) based solid state devices. Epitaxial Ni82.5Fe17.5 (permalloy, Py) thin films have been synthesized by pulsed laser deposition (PLD) on Si (1 0 0) using MgO/TiN as a template buffer. This epitaxial growth of these large lattice misfit systems was achieved through domain matching epitaxy (DME). The in-plane XRD pattern and selective area electron diffraction (SAED) results clearly indicate cube-on-cube epitaxial alignment. The bright field TEM image of Py/MgO/TiN/Si (1 0 0) heterostructure infers a Py layer thickness of ∼30 nm, with a well aligned island (150–200 nm) structure that is consistent with Volmer–Weber type growth. Magnetization data collected at 4 K and 300 K indicates that the easy axis of the magnetization lies in the plane of the Py. In addition, we have observed an intrinsic positive exchange bias (PEB) field of ∼104 Oe, where the magnetic hysteresis loop is shifted toward the positive field axis under zero field cooling conditions.}, number={1}, journal={CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE}, author={Rao, S. S. and Prater, J. T. and Wu, Fan and Nori, Sudhakar and Kumar, D. and Narayan, J.}, year={2014}, month={Feb}, pages={1–5} }
 @article{rao_prater_wu_shelton_maria_narayan_2013, title={Interface Magnetism in Epitaxial BiFeO3-La0.7Sr0.3MnO3 Heterostructures Integrated on Si(100)}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl4023435}, abstractNote={We report on the heteroepitaxial growth of ferroelectric (FE)-antiferromagnetic (AFM) BiFeO3 (BFO) on ferromagnetic La0.7Sr0.3MnO3 (LSMO), integrated on Si(100) using pulsed laser deposition via the domain matching epitaxy paradigm. The BFO/LSMO films were epitaxially grown on Si(100) by introducing epitaxial layers of SrTiO3/MgO/TiN. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photo absorption spectroscopy, and atomic force microscopy were employed to fully characterize the samples. Furthermore, we have investigated the magnetic behavior of this five layer heterostructure, in which a d(5) system (Fe(3+)) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn(3+)/Mn(4+) in LSMO. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetic moment and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of HEB when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetic moment and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom, similar to what has previously been reported in the literature. Future work will involve the linearly polarized X-ray absorption measurements to prove this hypothesis. This work represents a starting step toward the realization of magneto-electronic devices integrated with Si(100).}, number={12}, journal={NANO LETTERS}, author={Rao, S. S. and Prater, J. T. and Wu, Fan and Shelton, C. T. and Maria, J. -P. and Narayan, J.}, year={2013}, month={Dec}, pages={5814–5821} }
 @article{mal_nori_narayan_prater_avasthi_2013, title={Ion-irradiation-induced ferromagnetism in undoped ZnO thin films}, volume={61}, ISSN={["1359-6454"]}, DOI={10.1016/j.actamat.2012.09.071}, abstractNote={We have introduced defects in ZnO epitaxial thin films by swift heavy 107Ag9+ ion irradiation and investigated systematically their magnetic, electrical and optical properties. Oxygen annealed ZnO films are epitaxial single crystals that exhibit no long-range magnetic order. However, in this paper it is shown that room-temperature ferromagnetism (RTFM) can be introduced in a controlled manner in these films using ion irradiation and that the magnetization increases with ion dose. This qualitatively agrees with earlier studies which showed that RTFM could be induced in ZnO films through either vacuum thermal annealing or pulsed laser annealing below energy densities that lead to melting. Raman studies of the ion irradiated samples revealed dramatic changes in the vibration modes that correlated with increases in the carrier concentration, indicative of lattice disorder and defect creation. We compare these results with those observed in laser irradiated and vacuum annealed samples, and then discuss these findings in the context of defects and defect complexes created during the high-energy heavy ion irradiation process. We propose a unified mechanism to explain RTFM and n-type conductivity enhancements during irradiation, and laser and vacuum annealing.}, number={8}, journal={ACTA MATERIALIA}, author={Mal, Siddhartha and Nori, Sudhakar and Narayan, J. and Prater, J. T. and Avasthi, D. K.}, year={2013}, month={May}, pages={2763–2768} }
 @article{bayati_joshi_narayan_narayan_2013, title={Low-temperature processing and control of structure and properties of TiO2/c-sapphire epitaxial heterostructures}, volume={28}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2013.42}, abstractNote={Abstract}, number={13}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Bayati, Mohammad Reza and Joshi, Shivani and Narayan, Roger Jay and Narayan, Jay}, year={2013}, month={Jul}, pages={1669–1679} }
 @article{wu_zhu_narayan_2013, title={Macroscopic Twinning Strain in Nanocrystalline Cu}, volume={2}, ISSN={2166-3831}, url={http://dx.doi.org/10.1080/21663831.2013.862874}, DOI={10.1080/21663831.2013.862874}, abstractNote={Most deformation twins in nanocrystalline face-centered cubic (NC fcc) metals are reported to produce zero-macrostrain, which is attributed to either random activation of partials (RAP) or cooperative slip of three partials (CSTP). Here, we report that when the RAP mechanism is suppressed, ∼44% twins in NC Cu produced zero-macrostrain via the CSTP mechanism. This indicates that both RAP and CSTP are major mechanisms to generate zero-macrostrain twins. In addition, our results also indicate that stress state affects the twinning mechanism in NC fcc metals, and monotonic activation of partials with the same Burgers vector dominates twin formation under monotonic stress.}, number={2}, journal={Materials Research Letters}, publisher={Informa UK Limited}, author={Wu, F. and Zhu, Y.T. and Narayan, J.}, year={2013}, month={Nov}, pages={63–69} }
 @article{pennycook_zhou_chisholm_borisevich_varela_gazquez_pennycook_narayan_2013, title={Misfit accommodation in oxide thin film heterostructures}, volume={61}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2012.09.069}, abstractNote={Complex oxides are of intense interest due to their diverse properties, such as colossal magnetoresistance and superconductivity. Their complexity arises not only from the number of constituent elements, but also from their tolerance of non-stoichiometry and the structural complexity of these perovskite-based materials, e.g. the distortions and rotations of the oxygen octahedra surrounding the B-site cation. For these reasons, misfit accommodation in these materials is far more complex than in simpler materials, and can involve several different mechanisms simultaneously. In some cases, interfaces can be free from any misfit dislocations, lattice mismatch being accommodated via incorporation of oxygen vacancies, which take an ordered periodic arrangement. Interfaces may also present a perturbation to the octahedral rotations that can dramatically affect properties, not just close to the interface but through the entire film. In oxygen ion conducting materials, the oxygen sublattice may even melt in some situations.}, number={8}, journal={ACTA MATERIALIA}, author={Pennycook, S. J. and Zhou, H. and Chisholm, M. F. and Borisevich, A. Y. and Varela, M. and Gazquez, J. and Pennycook, T. J. and Narayan, J.}, year={2013}, month={May}, pages={2725–2733} }
 @article{molaei_bayati_alipour_estrich_narayan_2013, title={Nanosecond laser switching of surface wettability and epitaxial integration ofc-axis ZnO thin films with Si(111) substrates}, volume={26}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/26/1/015004}, DOI={10.1088/0953-8984/26/1/015004}, abstractNote={We have achieved integration of polar ZnO[0001] epitaxial thin films with Si(111) substrates where cubic yttria-stabilized zirconia (c-YSZ) was used as a template on a Si(111) substrate. Using XRD (θ–2θ and φ scans) and HRTEM techniques, the epitaxial relationship between the ZnO and the c-YSZ layers was shown to be [0001]ZnO ∥ [111]YSZ and [ 2 1 ̄ 1 ̄ 0 ] ZnO ∥ [ 1 ̄ 01 ] c - YSZ ?> , where the [ 2 1 ̄ 1 ̄ 0?> ] direction lies in the (0001) plane, and the [ 1 ̄ 01?> ] direction lies in the (111) plane. Similar studies on the c-YSZ/Si interface revealed epitaxy as 〈111〉YSZ ∥ 〈111〉Si and in-plane 〈110〉YSZ ∥ 〈110〉Si. HRTEM micrographs revealed atomically sharp and crystallographically continuous interfaces. The ZnO epilayers were subsequently laser annealed by a single pulse of a nanosecond excimer KrF laser. It was shown that the hydrophobic behavior of the pristine sample became hydrophilic after laser treatment. XPS was employed to study the effect of laser treatment on surface stoichiometry of the ZnO epilayers. The results revealed the formation of oxygen vacancies, which are envisaged to control the observed hydrophilic behavior. Our AFM studies showed surface smoothing due to the coupling of the high energy laser beam with the surface. The importance of integration of c-axis ZnO with Si(111) substrates is emphasized using the paradigm of domain matching epitaxy on the c-YSZ[111] buffer platform along with their out-of-plane orientation, which leads to improvement of the performance of the solid-state devices. The observed ultrafast response and switching in photochemical characteristics provide new opportunities for application of ZnO in smart catalysts, sensors, membranes, DNA self-assembly and multifunctional devices.}, number={1}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Molaei, R and Bayati, M R and Alipour, H M and Estrich, N A and Narayan, J}, year={2013}, month={Nov}, pages={015004} }
 @article{narayan_2013, title={Recent progress in thin film epitaxy across the misfit scale (2011 Acta Gold Medal Paper)}, volume={61}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2012.09.070}, abstractNote={This paper discusses recent progress in thin film epitaxy across the misfit scale through the paradigm of domain matching epitaxy (DME). This epitaxy across the misfit scale is critical for integrating multifunctionality on a chip and creating smart structures for next-generation solid-state devices. There are three sources of strains that are cumulative at the growth temperature, and the relaxation process starts during the growth process. Upon cooling, unrelaxed lattice, thermal and defect strains give rise to net residual strains. In large misfit (ε ⩾ 10%) systems, where lattice misfit strain is predominant, it can be relaxed completely, and then only thermal and defect strains remain upon cooling. In low misfit systems, all three sources contribute to the residual strain upon cooling, as result of incomplete lattice relaxation. The predominant strain relaxation mechanism in thin films is by nucleation of dislocations at the free surface, as the nucleation energy in the bulk is considerably higher. At the free surface, the activation barrier for dislocation nucleation is considerably lower at the steps. Since the step formation energy is lower under a compressive stress compared with tensile stress, it reduces nucleation energy under compressive stress and lowers the critical thickness compared with tensile stresses in thin films. Once the dislocation nucleates, it propagates or glides to the interface to relieve the strain. However, if lattice frictional stress in the film is high, most dislocations may not reach the interface, depending upon the growth temperature and rate. Thus, these two key steps, dislocation nucleation and propagation, play a critical role in the thin film relaxation process. Once the dislocations reach the interface, the atomic structure of the dislocation at the heterointerfaces determines its electronic properties, specifically trapping and recombination characteristics. It is found that the atomic structure of the dislocation is determined by the interplay between strain and chemical free energies. Thus, the dislocations (representing missing or extra planes) play a critical role in the relaxation of thin film heterostructures. This paper focuses on epitaxy across the misfit scale, based upon matching of integral multiples of lattice planes. If the misfit falls between the integral multiples, it is accommodated by the principle of domain variation, where domains alternate to accommodate the misfit. Details of epitaxy from low misfit (∼4%) in Ge/Si) to large misfit (∼22%) in TiN/Si are shown. In III-nitride/sapphire and II-oxide/sapphire systems, this paper deals with polar orientations, where misfit is uniform in the basal plane, and non-polar orientations, where misfit varies over an order of magnitude in the film plane. It is shown that the DME paradigm is key to the integration of thin film heterostructures across the misfit scale and other complex systems such as vanadium oxide and PZT systems on Si(1 0 0) substrates for the integration of functionalities on a computer chip. Finally, it is shown that the formation of epitaxial and self-assembled nanodots on Si(1 0 0) provides a critical advance, with tremendous implications for information and data storage and related nanomagnetics applications.}, number={8}, journal={ACTA MATERIALIA}, author={Narayan, J.}, year={2013}, month={May}, pages={2703–2724} }
 @article{zhu_chen_zhou_zhang_narayan_macmanus-driscoll_jia_wang_2013, title={Research Updates: Epitaxial strain relaxation and associated interfacial reconstructions: The driving force for creating new structures with integrated functionality}, volume={1}, ISSN={2166-532X}, url={http://dx.doi.org/10.1063/1.4828936}, DOI={10.1063/1.4828936}, abstractNote={Here, we report detailed strain mapping analysis at heterointerfaces of a new multiferroic complex oxide Bi3Fe2Mn2Ox(BFMO322) supercell and related layered structures. The state-of-the-art aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and the modified geometric phase analysis (GPA) have been used to characterize the self-assembled transitional layers, misfit defects, and, in particular, the biaxial lattice strain distributions. We found that not only a sufficient lattice misfit is required through substrate selection and to be preserved in initial coherent epilayer growth, but also an appropriate interfacial reconstruction is crucial for triggering the growth of the new BFMO322 supercell structure. The observation of new transitional interfacial phases behaving like coherent film layers within the critical thickness challenges the conventional understanding in existing epitaxial growth model.}, number={5}, journal={APL Materials}, publisher={AIP Publishing}, author={Zhu, Yuanyuan and Chen, Aiping and Zhou, Honghui and Zhang, Wenrui and Narayan, Jagdish and MacManus-Driscoll, Judith L. and Jia, Quanxi and Wang, Haiyan}, year={2013}, month={Nov}, pages={050702} }
 @article{bayati_molaei_budai_narayan_narayan_2013, title={Role of substrate crystallographic characteristics on structure and properties of rutile TiO2 epilayers}, volume={114}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4816470}, DOI={10.1063/1.4816470}, abstractNote={To investigate heterostructures of interest for catalytic applications, we integrated rutile TiO2 epitaxial thin films with Al2O3(0001), Al2O3(101¯0), and Al2O3(011¯2) substrates and studied structure and properties of the epilayers as a function of the crystallographic characteristics of the substrate. The epitaxial relationship across the film/substrate interfaces was established as (100)rutile‖(0001)c-sapphire and [001]rutile‖[101¯0]c-sapphire, (001)rutile‖[101¯0)m-sapphire, and [100]rutile‖[0001]m-sapphire, (101)rutile‖(011¯2)r-sapphire and [010]rutile‖(011¯2)r-sapphire. The origin and the relaxation mechanism of stress and strain for each heterostructure were studied in detail. It was revealed that large lattice misfit strains relax easily even if the primary slip system is not active due to the epitaxial alignment between the film and substrate and orientation of the in-plane stresses. We also showed that even small misfit strains can relax provided that the primary slip system is active. The origin of the residual strains in the epilayers was found to be primarily due to thermal misfit and defect/impurity strains. In addition, the decomposition rate of 4-chlorophenol by the rutile/sapphire heterostructures under ultraviolet illumination was measured. The (001)-plane was found to be the most photoactive face of rutile TiO2, while the (100)-plane showed the lowest photocatalytic activity. The difference in the photochemical characteristics was attributed to the atomic arrangement on different crystallographic surface planes.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bayati, M. R. and Molaei, R. and Budai, J. D. and Narayan, R. J. and Narayan, J.}, year={2013}, month={Jul}, pages={044314} }
 @article{narayan_2013, title={Selective-melt sintering brings speed and efficiency to creating high-density ceramics}, volume={171}, number={8}, journal={Advanced Materials & Processes}, author={Narayan, J.}, year={2013}, pages={29–33} }
 @article{bayati_alipour_joshi_molaei_narayan_narayan_misture_2013, title={Thin-Film Epitaxy and Enhancement of Photocatalytic Activity of Anatase/Zirconia Heterostructures by Nanosecond Excimer Laser Treatment}, volume={117}, ISSN={["1932-7447"]}, DOI={10.1021/jp400545t}, abstractNote={We present a novel method to improve the photocatalytic efficiency of epitaxial c-axis anatase TiO2 thin films by a factor of 2 by using nanosecond laser annealing. The anatase films were epitaxially grown by pulsed laser deposition on Si(001) substrates, where a tetragonal yttria-stabilized zirconia (t-YSZ) buffer was used to effectively remove the native SiOx layer from the substrates prior to deposition of anatase. With the information from X-ray and TEM diffraction patterns, the epitaxial relationship across the interfaces was shown to be: (001)[110]anatase||(001)[110]t-YSZ||(001)[001]silicon. Performing high-temperature XRD, we observed that the anatase epilayers were stable up to 1100 °C, far beyond the normal anatase-to-rutile transition temperature (approximately 600–700 °C). The samples were subsequently laser-annealed in air by a single pulse of KrF excimer laser beam at an energy density of ∼0.3 J.cm–2. On the basis of the detailed HRTEM studies, the interface between the laser annealed and the...}, number={14}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Bayati, M. R. and Alipour, H. M. and Joshi, S. and Molaei, R. and Narayan, R. J. and Narayan, J. and Misture, S. T.}, year={2013}, month={Apr}, pages={7138–7147} }
 @article{wu_wen_lavernia_narayan_zhu_2013, title={Twin intersection mechanisms in nanocrystalline fcc metals}, volume={585}, ISSN={["1873-4936"]}, DOI={10.1016/j.msea.2013.07.063}, abstractNote={Deformation twins have been reported to produce high strength and ductility. Intersections of deformation twins may affect the microstructural evolution during plastic deformation and consequently influence mechanical properties. However, the mechanisms governing twin-intersection behavior remain poorly understood. In this study, we investigated twin intersection mechanisms by observing twin transmission across the boundary of another twin using high-resolution transmission electron microscopy. Based on the experimental observations, mechanisms were proposed for twin–twin intersections and associated dislocation reactions in nanocrystalline fcc materials.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Wu, F. and Wen, H. M. and Lavernia, E. J. and Narayan, J. and Zhu, Y. T.}, year={2013}, month={Nov}, pages={292–296} }
 @article{bayati_joshi_molaei_narayan_narayan_2013, title={Ultrafast switching in wetting properties of TiO2/YSZ/Si(001) epitaxial heterostructures induced by laser irradiation}, volume={113}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4790327}, DOI={10.1063/1.4790327}, abstractNote={We have demonstrated dark hydrophilicity of single crystalline rutile TiO2(100) thin films, in which rapid switching from a hydrophobic to a hydrophilic surface was achieved using nanosecond excimer laser irradiation. The TiO2/YSZ/Si(001) single crystalline heterostructures were grown by pulsed laser deposition and were subsequently irradiated by a single pulse of a KrF excimer laser at several energies. The wettability of water on the surfaces of the samples was evaluated. The samples were hydrophobic prior to laser annealing and turned hydrophilic after laser annealing. Superhydrophilic surfaces were obtained at higher laser energy densities (e.g., 0.32 J.cm−2). The stoichiometries of the surface regions of the samples before and after laser annealing were examined using XPS. The results revealed the formation of oxygen vacancies on the surface, which are surmised to be responsible for the observed superhydrophilic behavior. According to the AFM images, surface smoothening was greater in films that were annealed at higher laser energy densities. The samples exhibited hydrophobic behavior after being placed in ambient atmosphere. The origin of laser induced wetting behavior was qualitatively understood to stem from an increase of point defects near the surface, which lowered the film/water interfacial energy. This type of rapid hydrophobic/hydrophilic switching may be used to facilitate fabrication of electronic and photonic devices with novel properties.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bayati, M. R. and Joshi, S. and Molaei, R. and Narayan, R. J. and Narayan, J.}, year={2013}, month={Feb}, pages={063706} }
 @article{chen_zhou_bi_zhu_luo_bayraktaroglu_phillips_choi_macmanus-driscoll_pennycook_et al._2013, title={A New Class of Room-Temperature Multiferroic Thin Films with Bismuth-Based Supercell Structure}, volume={25}, ISSN={["0935-9648"]}, DOI={10.1002/adma.201203051}, abstractNote={Intergrowth of two partially miscible phases of BiFeO(3) and BiMnO(3) gives a new class of room-temperature multiferroic phase, Bi(3) Fe(2) Mn(2) O(10+δ) , which has a unique supercell (SC) structure. The SC heterostructures exhibit simultaneously room-temperature ferrimagnetism and remanent polarization. These results open up a new avenue for exploring room-temperature single-phase multiferroic thin films by controlling the phase mixing of two perovskite BiRO(3) (R = Cr, Mn, Fe, Co, Ni) materials.}, number={7}, journal={ADVANCED MATERIALS}, author={Chen, Aiping and Zhou, Honghui and Bi, Zhenxing and Zhu, Yuanyuan and Luo, Zhiping and Bayraktaroglu, Adrian and Phillips, Jamie and Choi, Eun-Mi and MacManus-Driscoll, Judith L. and Pennycook, Stephen J. and et al.}, year={2013}, month={Feb}, pages={1028–1032} }
 @article{gupta_dutta_mal_narayan_2012, title={Controlledp-type ton-type conductivity transformation in NiO thin films by ultraviolet-laser irradiation}, volume={111}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3671412}, DOI={10.1063/1.3671412}, abstractNote={We report the systematic changes in structural, electrical, and optical properties of NiO thin films on c-sapphire introduced by nanosecond ultraviolet excimer laser pulses. Epitaxial nature of as deposited NiO was determined by x-ray diffraction phi scans and transmission electron microscopy (TEM) and it was established that NiO film growth takes place with twin domains on sapphire where two types of domains have 60° in-plane rotation with respect to each other about the [111] growth direction. We determined that at pulsed laser energy density of 0.275 J/cm2, NiO films exhibited conversion from p-type semiconducting to n-type conductive behavior with three orders of magnitude decrease in resistivity, while maintaining its cubic crystal structure and good epitaxial relationship. Our TEM and electron-energy-loss spectroscopy studies conclusively ruled out the presence of any Ni clustering or precipitation due to the laser treatment. The laser-induced n-type carrier transport and conductivity enhancement were shown to be reversible through subsequent thermal annealing in oxygen. This change in conductivity behavior was correlated with the nonequilibrium concentration of laser induced Ni0-like defect states.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Gupta, Pranav and Dutta, Titas and Mal, Siddhartha and Narayan, Jagdish}, year={2012}, month={Jan}, pages={013706} }
 @article{bayati_ding_lee_narayan_narayan_zhou_pennycook_2012, title={Defect mediated photocatalytic decomposition of 4-chlorophenol on epitaxial rutile thin films under visible and UV illumination}, volume={24}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/24/39/395005}, DOI={10.1088/0953-8984/24/39/395005}, abstractNote={We show that pure rutile TiO2 can be photo-responsive even under low energy visible light after annealing in vacuum where we envisage that the point defects, i.e. oxygen vacancies and titanium interstitials, serve an important role. In this study, single crystal rutile films were grown by the pulsed laser deposition technique and then vacuum annealed under different oxygen pressures to introduce defects into their lattices. 4-chlorophenol was selected as a model material and decomposed by the annealed TiO2 films where the maximum photocatalytic reaction rate constants were determined as 0.0107 and 0.0072 min−1 under UV and visible illumination. Epitaxial growth along the [200] direction was confirmed by φ-scan and 2θ-scan XRD and the epitaxial relationship between the rutile film and the c-sapphire substrate was explained as ( 1 0 0 ) [ 0 1 0 ] R ‖ ( 0 0 0 1 ) [ 1 2 ̄ 1 0 ] S ?> . The formation of atomically sharp interfaces and the epitaxial growth were ascertained by annular dark-field STEM imaging. Based on the XPS, UV–vis and PL spectroscopy results, it was found that the defect concentration increased after annealing under lower pressures, e.g. 5 × 10−6 Torr. In contrast, more perfect crystals were obtained when the films were annealed under high oxygen pressures, namely 5 × 101 Torr. The morphology of the films was also investigated by employing an AFM technique. It was observed that increase of the annealing pressure results in the formation of larger grains. It was also found that the electrical resistivity of the rutile films strongly increased by about three orders of magnitude when the annealing pressure increased from 5 × 10−4 to 5 × 101 Torr.}, number={39}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Bayati, M R and Ding, J and Lee, Y F and Narayan, R J and Narayan, J and Zhou, H and Pennycook, S J}, year={2012}, month={Sep}, pages={395005} }
 @article{mal_nori_mula_narayan_prater_2012, title={Defect mediated reversible ferromagnetism in Co and Mn doped zinc oxide epitaxial films}, volume={112}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4768721}, DOI={10.1063/1.4768721}, abstractNote={We have introduced defects in ZnO (undoped and doped with Co and Mn) epitaxial thin films using laser irradiation from nanosecond laser pulses and thermal annealing in oxygen ambient. In contrast to the as grown samples, the laser irradiated films show a significant increase in conductivity, enhancement in UV emission, while maintaining the same wurtzite crystal structure. Room-temperature ferromagnetism (RTFM) is observed in laser-irradiated samples, which increased with the number of laser pulses up to a certain value where magnetic moment saturates. The induced ferromagnetism as well as the enhanced electrical conductivity can be reversed with thermal annealing in oxygen ambient. The magnetization in Co and Mn doped films was found to be strong function of growth conditions and defect concentration. X-ray diffraction and optical absorption experiments suggested a 2+ valance state and tetrahedral coordination for both Co and Mn ions. There is a simultaneous increase in n-type electrical conductivity with the number of laser pulses and continue to exhibit semiconducting behavior in both undoped and doped films. The saturation magnetization was found to be 0.08 μB/Co and 0.05 μB/Mn, much lower than 3.0 μB/Co and 5.0 μB/Mn, indicating the prominent role of intrinsic defects in RTFM with some contribution from Co2+-oxygen vacancy complexes. We propose a unified mechanism based upon introduction of intrinsic defects to explain RTFM and n-type conductivity enhancements during pulsed laser and thermal annealing.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mal, Siddhartha and Nori, Sudhakar and Mula, Suhrit and Narayan, J. and Prater, J. T.}, year={2012}, month={Dec}, pages={113917} }
 @article{ma_prater_sudakar_rosenberg_narayan_2012, title={Defects in room-temperature ferromagnetic Cu-doped ZnO films probed by x-ray absorption spectroscopy}, volume={24}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/24/30/306002}, DOI={10.1088/0953-8984/24/30/306002}, abstractNote={We report a comprehensive study of the defects in room-temperature ferromagnetic (RTFM) Cu-doped ZnO thin films using x-ray absorption spectroscopy. The films are doped with 2 at.% Cu, and are prepared by reactive magnetron sputtering (RMS) and pulsed laser deposition (PLD), respectively. The results reveal unambiguously that atomic point defects exist in these RTFM thin films. The valence states of the Cu ions in both films are 2+. In the film prepared by PLD, the oxygen vacancies (VO) form around both Zn ions and Cu ions in the hexagonal wurtzite structure. Upon annealing of the film in O2, the VO population reduces and so does the RTFM. In the film prepared by RMS, the VOs around Cu ions are not detected, and the VO population around Zn ions is also smaller than in the PLD-prepared film. However, zinc vacancies (VZn) are evidenced. Given the low doping level of spin-carrying Cu ions, these results provide strong support for defect-mediated ferromagnetism in Cu-doped ZnO thin films.}, number={30}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Ma, Q and Prater, J T and Sudakar, C and Rosenberg, R A and Narayan, J}, year={2012}, month={Jul}, pages={306002} }
 @article{bayati_molaei_narayan_narayan_zhou_pennycook_2012, title={Domain epitaxy in TiO2/alpha-Al2O3 thin film heterostructures with Ti2O3 transient layer}, volume={100}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4729937}, DOI={10.1063/1.4729937}, abstractNote={Rutile TiO2 films were grown epitaxially on α-alumina (sapphire(0001)) substrates and characterized by x-ray diffraction and scanning transmission electron microscopy. It was revealed that the rutile film initially grows pseudomorphically on sapphire as Ti2O3 and, after a few monolayers, it grows tetragonally on the Ti2O3/sapphire platform. Formation of the Ti2O3 transient layer was attributed to the symmetry mismatch between tetragonal structure of TiO2 and hexagonal structure of alumina. The separation between the ½[101¯](101) misfit dislocations was dictated by Ti2O3 and was determined to be 9.7 Å which is consistent with 4/3 and 3/2 alternating domains across the film/substrate interface.}, number={25}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Bayati, M.R. and Molaei, R. and Narayan, J. and Narayan, R.J. and Zhou, H. and Pennycook, S.J.}, year={2012}, month={Jun}, pages={251606} }
 @article{narayan_2012, title={Nanoscience to nanotechnology to manufacturing transition}, volume={9}, number={10-12}, journal={International Journal of Nanotechnology}, author={Narayan, J.}, year={2012}, pages={914–941} }
 @article{bayati_gupta_molaei_narayan_narayan_2012, title={Phase Tuning, Thin Film Epitaxy, Interfacial Modeling, and Properties of YSZ-Buffered TiO2 on Si(001) Substrate}, volume={12}, ISSN={1528-7483 1528-7505}, url={http://dx.doi.org/10.1021/cg3007124}, DOI={10.1021/cg3007124}, abstractNote={We have studied systematically the influence of pulsed laser deposition variables on microstructure and properties of TiO2 epitaxial thin films where integration with Si(100) substrate was achieved by cubic yttria-stabilized-zirconia (c-YSZ) buffer layer. Details of crystallographic and atomic arrangements across the interfaces are discussed in the light of the domain matching epitaxy paradigm. The single crystalline rutile films were obtained at higher substrate temperatures and lower oxygen pressures; whereas, the growth of epitaxial anatase films was promoted by decreasing the temperature and increasing the oxygen pressure. We showed that crystallographic structure of the TiO2 films is determined mainly by the termination structure of the c-YSZ layer and the bonding characteristics across the TiO2/c-YSZ interface. Using 2θ and φ scans of XRD, the epitaxial relationship between Si(100) substrate and the zirconia buffer layer was shown to be cube-on-cube: (001)[100]YSZ∥(001)[100]Si. Furthermore, the epit...}, number={9}, journal={Crystal Growth & Design}, publisher={American Chemical Society (ACS)}, author={Bayati, M. R. and Gupta, P. and Molaei, R. and Narayan, R. J. and Narayan, J.}, year={2012}, month={Aug}, pages={4535–4544} }
 @article{bharathan_narayan_rozgonyi_bulman_2013, title={Poisson Ratio of Epitaxial Germanium Films Grown on Silicon}, volume={42}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-012-2337-6}, abstractNote={An accurate knowledge of elastic constants of thin films is important in understanding the effect of strain on material properties. We have used residual thermal strain to measure the Poisson ratio of Ge films grown on Si ⟨001⟩ substrates, using the sin2 ψ method and high-resolution x-ray diffraction. The Poisson ratio of the Ge films was measured to be 0.25, compared with the bulk value of 0.27. Our study indicates that use of Poisson ratio instead of bulk compliance values yields a more accurate description of the state of in-plane strain present in the film.}, number={1}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Bharathan, Jayesh and Narayan, Jagdish and Rozgonyi, George and Bulman, Gary E.}, year={2013}, month={Jan}, pages={40–46} }
 @article{bayati_joshi_molaei_narayan_narayan_2012, title={Structure-property correlation in epitaxial (200) rutile films on sapphire substrates}, volume={187}, ISSN={["0022-4596"]}, DOI={10.1016/j.jssc.2012.01.031}, abstractNote={We have investigated the influence of the deposition variables on photocatalytic properties of epitaxial rutile films. Despite a large lattice misfit of rutile with sapphire substrate, (2 0 0) epitaxial layers were grown on (0 0 0 1)sapphire by domain matching epitaxy paradigm. Using φ-scan XRD and cross section TEM, the epitaxial relationship was determined to be rutile(1 0 0)||sapphire(0 0 0 1), rutile(0 0 1)||sapphire(1 0 −1 0), and rutile(0 1 0)||sapphire(1 −2 1 0). Based on the XRD patterns, increasing the repetition rate introduced tensile stress along the film normal direction, which may arise as a result of trapped defects. Formation of such defects was studied by UV–VIS, PL, and XPS techniques. AFM studies showed that the film roughness increases with the repetition rate. Finally, photocatalytic performance of the layers was investigated through measuring decomposition rate of 4-chlorophenol on the films surface. The films grown at higher frequencies revealed higher photocatalytic efficiency. This behavior was mainly related to formation of point defects which enhance the charge separation.}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Bayati, M. R. and Joshi, Sh and Molaei, R. and Narayan, R. J. and Narayan, J.}, year={2012}, month={Mar}, pages={231–237} }
 @article{molaei_bayati_narayan_2012, title={Thin film epitaxy and near bulk semiconductor to metal transition in VO2/NiO/YSZ/Si(001) heterostructures}, volume={27}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2012.374}, abstractNote={Abstract}, number={24}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Molaei, Roya and Bayati, Mohammad Reza and Narayan, Jagdish}, year={2012}, month={Dec}, pages={3103–3109} }
 @article{yang_nori_mal_narayan_2011, title={Control of room-temperature defect-mediated ferromagnetism in VO2 films}, volume={59}, ISSN={["1359-6454"]}, DOI={10.1016/j.actamat.2011.06.047}, abstractNote={We report interesting ferromagnetic properties and their control in a vanadium-based oxide system driven by stoichiometric defects. Vanadium oxide (VO2) thin films were grown on c-plane sapphire substrates by a pulsed laser deposition technique under different ambient conditions. The ferromagnetism of the epitaxial VO2 films can be switched on and off by altering the cooling ambient parameters. In addition, the saturated magnetic moments and coercivity of the VO2 films were found to be a function of the oxygen partial pressure during the growth process. The room-temperature ferromagnetic properties of VO2 films were correlated with the nature of the microstructure and the growth parameters. The origin of the induced magnetic properties are qualitatively understood to stem from intrinsic structural and stoichiometric defects.}, number={16}, journal={ACTA MATERIALIA}, author={Yang, Tsung-Han and Nori, Sudhakar and Mal, Siddhartha and Narayan, Jagdish}, year={2011}, month={Sep}, pages={6362–6368} }
 @article{mal_nori_narayan_prater_2011, title={Defect-mediated ferromagnetism and controlled switching characteristics in ZnO}, volume={26}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2011.74}, abstractNote={Abstract}, number={10}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Mal, Siddhartha and Nori, Sudhakar and Narayan, Jagdish and Prater, John T.}, year={2011}, month={May}, pages={1298–1308} }
 @article{gupta_singhal_narayan_avasthi_2011, title={Electronic excitation induced controlled modifications of semiconductor-to-metal transition in epitaxial VO2 thin films}, volume={26}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2011.392}, abstractNote={Abstract}, number={23}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Gupta, Alok and Singhal, Rahul and Narayan, Jagdish and Avasthi, Devesh K.}, year={2011}, month={Dec}, pages={2901–2906} }
 @article{yang_mal_jin_narayan_narayan_2011, title={Epitaxial VO2/Cr2O3/sapphire heterostructure for multifunctional applications}, volume={98}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3541649}, DOI={10.1063/1.3541649}, abstractNote={In this letter, we report integration of magnetic and ultrafast-transition properties of VO2 films with antiferromagnetic (AFM) Cr2O3 template layer in the epitaxial VO2/Cr2O3/Al2O3 heterostructure The Cr2O3 is an AFM material, which can pin the spin momentum of ferromagnetic VO2, in addition to providing epitaxial template. Thus, the magnetic properties of VO2 films grown with Cr2O3 buffer layer can be improved for multifunctional magnetic tunnel junctions and sensor applications. Electrical resistivity measurements as a function of temperature showed a sharp transition width (1.94 °C), with a small hysteresis width (5.7 °C), and large resistance change (∼3.8×104) across the semiconductor to metal transition (SMT). We discuss the correlations of the magnetic properties and SMT characteristics with epitaxial growth and formation of twins.}, number={2}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Yang, Tsung-Han and Mal, S. and Jin, C. and Narayan, R. J. and Narayan, J.}, year={2011}, month={Jan}, pages={022105} }
 @article{zhou_chisholm_yang_pennycook_narayan_2011, title={Role of interfacial transition layers in VO2/Al2O3 heterostructures}, volume={110}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3642980}, DOI={10.1063/1.3642980}, abstractNote={Epitaxial VO2 films grown by pulsed laser deposition (PLD) on c-cut sapphire substrates ((0001) Al2O3) were studied by aberration-corrected scanning transmission electron microscopy (STEM). A number of film/substrate orientation relationships were found and are discussed in the context of the semiconductor-metal transition (SMT) characteristics. A structurally and electronically modified buffer layer was revealed on the interface and was attributed to the interface free-energy minimization process of accommodating the symmetry mismatch between the substrate and the film. This interfacial transition layer is expected to affect the SMT behavior when the interfacial region is a significant fraction of the VO2 film thickness.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Zhou, H. and Chisholm, M. F. and Yang, Tsung-Han and Pennycook, S. J. and Narayan, J.}, year={2011}, month={Oct}, pages={073515} }
 @article{goyal_narayan_lin_2011, title={Self-assembly and directed assembly of advanced materials introduction}, volume={26}, number={2}, journal={Journal of Materials Research}, author={Goyal, A. and Narayan, J. and Lin, Q. H.}, year={2011}, pages={109–110} }
 @article{mal_yang_gupta_prater_narayan_2011, title={Thin film epitaxy and magnetic properties of STO/TiN buffered ZnO on Si(001) substrates}, volume={59}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2010.12.058}, abstractNote={Abstract We report integration of epitaxial ZnO films with Si(0 0 1) substrates using STO/TiN buffer layers. It has been demonstrated that the preferential orientation of the a-plane ( 1 1 2 ¯ 0 ) and c-plane (0 0 0 2) of ZnO can be controlled via deposition temperature and oxygen partial pressure. At lower substrate temperatures ZnO grows solely in the (0 0 0 2) orientation, while the ( 1 1 2 ¯ 0 ) orientation was dominant at high substrate temperatures and low oxygen pressures. At higher pressures, the (0 0 0 2) orientation is preferred, while ( 1 1 2 ¯ 0 ) becomes weaker and a ( 1 0 1 ¯ 2 ) ZnO appears. Epitaxial relationships have been determined from X-ray diffraction φ-scans and it was found that both c- and a-ZnO had two types of orientations due to the cubic symmetry of the STO buffer layer. The orientation relationship of c-ZnO on STO(0 0 1) was ZnO(0 0 0 1) ∥ STO(1 0 0); ZnO[ 1 1 2 ¯ 0 ] ∥ STO[1 1 0] and ZnO[ 1 ¯ 2 1 ¯ 0 ] ∥ STO[ 1 ¯ 1 0 ], while that of a-ZnO on STO(0 0 1) was ZnO( 1 1 2 ¯ 0 ) ∥ STO(1 0 0); ZnO[ 1 1 2 ¯ 0 ] ∥ STO[1 1 0] and ZnO[0 0 0 2] ∥ STO[ 1 ¯ 1 0 ]. High-resolution transmission electron microscopy studies revealed atomically sharp interfaces with no reaction at the interface. Reversible d0 ferromagnetism was found to be present in both ZnO and STO layers. Our electron-energy-loss spectroscopy studies conclusively rule out the presence of any external ferromagnetic ions or impurities. Taken together, our data indicate that the ferromagnetic order in these undoped oxides might be defect mediated.}, number={6}, journal={ACTA MATERIALIA}, author={Mal, Siddhartha and Yang, Tsung-Han and Gupta, P. and Prater, J. T. and Narayan, J.}, year={2011}, month={Apr}, pages={2526–2534} }
 @article{nori_yang_narayan_2011, title={VO2 thin films: Defect mediation in room temperature ferromagnetic switching characteristics}, volume={63}, ISSN={1047-4838 1543-1851}, url={http://dx.doi.org/10.1007/s11837-011-0170-7}, DOI={10.1007/s11837-011-0170-7}, number={10}, journal={JOM}, publisher={Springer Science and Business Media LLC}, author={Nori, Sudhakar and Yang, T. -H. and Narayan, Jagdish}, year={2011}, month={Oct}, pages={29–33} }
 @article{mal_yang_jin_nori_narayan_prater_2011, title={d(0) Ferromagnetism in undoped ZnO thin films: Effect of thickness, interface and oxygen annealing}, volume={65}, DOI={10.1016/j.scriptamat.2011.09.016}, abstractNote={We present a systematic study of the thickness dependency of the structural, electrical and magnetic properties of undoped ZnO thin films. The highest saturation moment (∼36.75 emu cm−3) was observed for the thinnest films. Both the undoped and 5% Co doped ZnO films of different thickness (0.066–1.1 μm) showed a diamagnetic behavior upon annealing in oxygen. Activation energy of quenching of ferromagnetism revealed oxygen vacancies as the key mediating defect in ferromagnetic ZnO thin films.}, number={12}, journal={Scripta Materialia}, author={Mal, Siddhartha and Yang, Tsung-Han and Jin, Chunming and Nori, Sudhakar and Narayan, Jagdish and Prater, John T.}, year={2011}, month={Jan}, pages={1061–1064} }
 @article{zhou_chisholm_pant_gazquez_pennycook_narayan_2010, title={Atomic Resolution Z-Contrast Imaging of the Interface Between Non-Polar a-ZnO Grown on r-Cut Al2O3 by Pulsed Laser Deposition}, volume={16}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927610061349}, DOI={10.1017/S1431927610061349}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Zhou, H and Chisholm, MF and Pant, P and Gazquez, J and Pennycook, SJ and Narayan, J}, year={2010}, month={Jul}, pages={154–155} }
 @article{zhou_chisholm_pant_chang_gazquez_pennycook_narayan_2010, title={Atomic structure of misfit dislocations in nonpolar ZnO/Al2O3 heterostructures}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3489687}, DOI={10.1063/1.3489687}, abstractNote={Understanding dislocation core structures at the atomic level is of significant theoretical and technological importance because of the role dislocations play in the electronic/optical properties of materials. In this paper, we report our aberration-corrected scanning transmission electron microscopy study on misfit dislocation core structures at non-polar (112¯0)ZnO/(11¯02)Al2O3 (a-ZnO/r-Al2O3) interface. The atomic configuration of the core structure is found to be closely related to the preferred interfacial bonding configuration. A significant number of these misfit dislocations have undergone a core structure modification involving the incorporation of Zn in the Al2O3 side of the dislocation.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Zhou, H. and Chisholm, M. F. and Pant, P. and Chang, H. J. and Gazquez, J. and Pennycook, S. J. and Narayan, J.}, year={2010}, month={Sep}, pages={121914} }
 @article{mal_narayan_nori_prater_kumar_2010, title={Defect-mediated room temperature ferromagnetism in zinc oxide}, volume={150}, ISSN={["0038-1098"]}, DOI={10.1016/j.ssc.2010.06.030}, abstractNote={We have introduced systematic changes in the electrical, magnetic and optical properties of undoped ZnO films through irradiation with an UV Excimer laser. Increases in the electrical conductivity and magnetic moment have been controlled precisely with the number of laser pulses, without altering the Wurtzite crystal structure and n-type semiconducting characteristics of the films. The laser induced ferromagnetism and concomitant conductivity enhancement can be reversed through subsequent thermal annealing. Hence, we have successfully demonstrated reversible switching of RTFM in undoped ZnO by employing oxygen annealing (off) and laser irradiation (on). We discuss these findings in terms of defects and defect complexes created by pulsed laser irradiation.}, number={35-36}, journal={SOLID STATE COMMUNICATIONS}, author={Mal, Siddhartha and Narayan, J. and Nori, Sudhakar and Prater, J. T. and Kumar, D.}, year={2010}, month={Sep}, pages={1660–1664} }
 @article{zhu_wu_liao_narayan_kecskes_mathaudhu_2011, title={Dislocation-twin interactions in nanocrystalline fcc metals}, volume={59}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2010.10.028}, abstractNote={Dislocation interaction with and accumulation at twin boundaries have been reported to significantly improve the strength and ductility of nanostructured face-centered cubic (fcc) metals and alloys. Here we systematically describe plausible dislocation interactions at twin boundaries. Depending on the characteristics of the dislocations and the driving stress, possible dislocation reactions at twin boundaries include cross-slip into the twinning plane to cause twin growth or de-twinning, formation of a sessile stair-rod dislocation at the twin boundary, and transmission across the twin boundary. The energy barriers for these dislocation reactions are described and compared.}, number={2}, journal={ACTA MATERIALIA}, author={Zhu, Y. T. and Wu, X. L. and Liao, X. Z. and Narayan, J. and Kecskes, L. J. and Mathaudhu, S. N.}, year={2011}, month={Jan}, pages={812–821} }
 @article{dutta_gupta_gupta_narayan_2010, title={Effect of Li doping in NiO thin films on its transparent and conducting properties and its application in heteroepitaxial p-n junctions}, volume={108}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3499276}, DOI={10.1063/1.3499276}, abstractNote={Li doped NiO (LixNi1−xO) thin films were epitaxially grown along [111] orientation on c-sapphire by pulsed laser deposition. The structural, electrical, and optical properties of the films were investigated using x-ray diffraction, four probe technique, and UV-visible spectra, respectively. The epitaxial growth of [111] Li doped NiO on [0001] sapphire was determined by using high resolution x-ray Φ scan. Effects of the deposition condition and Li doping concentration variations on the electrical and optical properties of Li doped NiO films were also investigated. The analysis of the resistivity data show that doped Li ions occupy the substitutional sites in the films, enhancing the p-type conductivity. The minimum resistivity of 0.15 Ω cm was obtained for Li0.07Ni0.93O film. The activation energy of Li doped NiO films were estimated to be in the range of 0.11–0.14 eV. Based upon these values, a possible electrical transport mechanism is discussed. A p-n heterojunction has also been fabricated for the optimized p-Li doped NiO with n-ZnO. The insertion of i-MgZnO between the p and n layer led to improved current-voltage characteristics due to reduced leakage current. In the diode architecture, a heteroepitaxial relationship of [111]NiO‖[0001]MgZnO‖[0001]ZnO‖[0001]GZO‖[0001]Al2O3 among the layers was obtained. The p-i-n heterojunction showed good rectification behavior with turn on voltage of 2.8 V and breakdown voltage of 8.0 V.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Dutta, Titas and Gupta, P. and Gupta, A. and Narayan, J.}, year={2010}, month={Oct}, pages={083715} }
 @article{dutta_gupta_gupta_narayan_2010, title={High work function (p-type NiO1+x)/Zn0.95Ga0.05O heterostructures for transparent conducting oxides}, volume={43}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/43/10/105301}, DOI={10.1088/0022-3727/43/10/105301}, abstractNote={We report the growth and properties of heterostructure thin films consisting of a thin overlayer of p-NiO1+x on Zn0.95Ga0.05O (GZO) by pulsed laser deposition for transparent electrode applications. The GZO films with a thin p-type NiO1+x overlayer exhibited a higher work function. It is envisaged to facilitate hole injection across the heterojunction in a solid state device resulting in improved device efficiency. The crystalline quality of the bilayer films was investigated by x-ray diffraction. NiO1+x overlayers showed the preferred orientation along the [1 1 1] direction on Zn0.95Ga0.05O (0 0 0 1) films deposited on a glass substrate while they were epitaxial when the substrate used was sapphire. The effects of the NiO1+x overlayer thickness variation and Li doping on the electrical and optical properties of NiO1+x/Zn0.95Ga0.05O bilayer films were also investigated. The bilayer films with an optimized overlayer thickness showed good optical transparency (⩾85%) and low resistivity of ∼10−4 Ω cm up to temperatures as low as 100 K. Using x-ray photoelectron spectroscopy it has been established that nickel in NiO1+x exists in multiple oxidation states of Ni2+ and Ni3+. The presence of Ni3+ gives rise to p-type conductivity in non-stoichiometric NiO1+x. Additionally, ultraviolet photoelectron spectroscopy studies showed that the bilayer films have high work function values ranging from 5.2 to 5.3 eV. A correlation between the surface work function and Ni3+/Ni2+ ratio has also been established.}, number={10}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Dutta, Titas and Gupta, Pranav and Gupta, Alok and Narayan, Jagdish}, year={2010}, month={Feb}, pages={105301} }
 @article{jin_aggarwal_wei_nori_kumar_ponarin_smirnov_narayan_narayan_2011, title={Intrinsic Room-Temperature Ferromagnetic Properties of Ni-Doped ZnO Thin Films}, volume={42}, ISSN={1073-5623 1543-1940}, url={http://dx.doi.org/10.1007/S11661-010-0479-9}, DOI={10.1007/s11661-010-0479-9}, number={11}, journal={Metallurgical and Materials Transactions A}, publisher={Springer Science and Business Media LLC}, author={Jin, C. and Aggarwal, R. and Wei, W. and Nori, S. and Kumar, D. and Ponarin, D. and Smirnov, A. I. and Narayan, J. and Narayan, R. J.}, year={2011}, month={Nov}, pages={3250–3254} }
 @article{wei_nori_jin_narayan_narayan_ponarin_smirnov_2010, title={Mott transition in Ga-doped MgxZn1-xO: A direct observation}, volume={171}, ISSN={["1873-4944"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77953133966&partnerID=MN8TOARS}, DOI={10.1016/j.mseb.2010.03.078}, abstractNote={This paper reports the direct evidence for Mott transition in Ga-doped MgxZn1−xO thin films. Highly transparent Ga-doped MgxZn1−xO thin films were grown on c-plane sapphire substrates using pulsed laser deposition. 0.1 at.%, 0.5 at.% and 1 at.% Ga-doped Mg0.1Zn0.9O films were selected for resistivity measurements in the temperature range from 250 K to 40 mK. The 0.1 at.% Ga-doped Mg0.1Zn0.9O thin film showed typical insulator-like behavior and the 1 at.% Ga-doped Mg0.1Zn0.9O thin film showed typical metal-like behavior. The 0.5 at.% Ga-doped Mg0.1Zn0.9O film showed increasing resistivity with decreasing temperature; resistivity was saturated with a value of 1.15 × 10−2 Ω cm at 40 mK, which is characteristic of the metal–insulator transition region. Temperature-dependent conductivity σ(T) in the low temperature range revealed that the electron-electron scattering is the dominant dephasing mechanism. The inelastic scattering time is found to vary as T−3/2.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS}, publisher={Elsevier BV}, author={Wei, Wei and Nori, Sudhakar and Jin, Chunming and Narayan, Jagdish and Narayan, Roger J. and Ponarin, Dmtri and Smirnov, Alex}, year={2010}, month={Jul}, pages={90–92} }
 @article{gupta_narayan_dutta_2010, title={Near bulk semiconductor to metal transition in epitaxial VO2 thin films}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3503632}, DOI={10.1063/1.3503632}, abstractNote={We have been able to achieve semiconductor-to-metal transition (SMT) temperature in VO2 thin films close to the values reported for bulk VO2 single crystals. This was achieved by complete relaxation of misfit strain, which leads to a negligible tension/compression along VO2 [001], upon introduction of NiO buffer layer on c-plane sapphire substrate. In this paper, we discuss the mechanism behind complete relaxation of misfit strain which occurs under the paradigm of domain-matching epitaxy, where integral multiples of planes match across the interface. NiO buffer layers were grown in situ, prior to the VO2 deposition, using pulsed-laser deposition technique. X-ray θ-2θ, φ, and pole figure scans were performed for structural characterization of the VO2/NiO/Al2O3 (0001) heterostructure. All the constituent layers of the heterostructure were found to be epitaxial with orientation relationship: (020)VO2∥(111)NiO∥(0001)Al2O3 and ⟨100⟩VO2∥⟨110⟩NiO∥⟨101¯0⟩Al2O3. Parameters related to SMT, such as hysteresis and transition width were extracted from the Gaussian fit of temperature dependence of electrical resistance. These parameters have also been discussed in correlation with the strain along c-axis of VO2, in-plane orientation, and microstructure. A comparison has been made between the VO2 thin films deposited with and without NiO buffer layer on c-sapphire substrates to delineate the importance of strain relaxation in attaining near bulk SMT temperature values.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gupta, Alok and Narayan, Jagdish and Dutta, Titas}, year={2010}, month={Oct}, pages={151912} }
 @article{yang_jin_aggarwal_narayan_narayan_2010, title={On growth of epitaxial vanadium oxide thin film on sapphire (0001)}, volume={25}, ISSN={["2044-5326"]}, DOI={10.1557/jmr.2010.0059}, abstractNote={We report the characteristics of epitaxial growth and properties of vanadium oxide (VO2) thin films on sapphire (0001) substrates. Pulsed laser deposition was used to grow (002) oriented VO2 films on sapphire (0001). Transmission electron microscopy studies showed that the orientation relationship between the substrate and the thin film is: (002)f2∥(0006)sub3 and [010]f2 ∥sub. It was also established that VO2 has three different orientations in the film plane which are rotated by 60° from each other. The epitaxial growth of vanadium oxide on sapphire (0001) has been explained in the framework of domain matching epitaxy (DME). Electrical resistivity measurements as a function of temperature showed a sharp transition with a hysteresis width ˜5 °C, and large resistance change (˜1.5 × 104) from the semiconductor phase to the metal phase. It is interesting to note that in spite of large angle twin boundaries in these VO2 films, the SMT characteristics are better than those observed for polycrystalline films. The higher width of thermal hysteresis for the VO2 film on c-sapphire compared to a bulk single VO2 crystal and a single-crystal VO2 film on r-sapphire can be attributed to the existence of these large-angle twin grain boundaries. These findings can provide insight into the phase transformation characteristics of VO2, which has important applications in switching and memory devices.}, number={3}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Yang, Tsung-Han and Jin, Chunming and Aggarwal, Ravi and Narayan, R. J. and Narayan, Jay}, year={2010}, month={Mar}, pages={422–426} }
 @article{wei_jin_narayan_narayan_2010, title={Optical and electrical properties of gallium-doped MgxZn1−xO}, volume={107}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3271415}, DOI={10.1063/1.3271415}, abstractNote={In this study, the optical and electrical properties of epitaxial single crystal gallium-doped MgxZn1−xO thin films grown on c-plane sapphire substrates by pulsed laser deposition were investigated. In these films, the Ga content was varied from 0.05 to 7 at. % and the Mg content was varied from 5 to 15 at. %. X-ray diffraction showed that the solid solubility limit of Ga in MgxZn1−xO is less than 3 at. %. The absorption spectra were fitted to examine Ga doping effects on bandgap and band tail characteristics. Distinctive trends in fitted bandgap and band tail characteristics were determined in films with Ga content below 3 at. % and Ga content above 3 at. %. The effects of bandgap engineering on optical transparency were evaluated using transmission spectra. Carrier concentration and Hall mobility data were obtained as functions of Ga content and Mg content. The electrical properties were significantly degraded when the Ga content exceeded 3 at. %. Correlations between conduction mechanisms and gallium doping of MgxZn1−xO thin films were described. In addition, the effect of bandgap engineering on the electrical properties of epitaxial single crystal gallium-doped MgxZn1−xO thin films was discussed.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Wei, Wei and Jin, Chunming and Narayan, Jagdish and Narayan, Roger J.}, year={2010}, month={Jan}, pages={013510} }
 @article{mal_nori_jin_narayan_nellutla_smirnov_prater_2010, title={Reversible room temperature ferromagnetism in undoped zinc oxide: Correlation between defects and physical properties}, volume={108}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3491037}, DOI={10.1063/1.3491037}, abstractNote={We report a systematic study of the structural, chemical, electrical, optical, and magnetic properties of undoped ZnO thin films grown under different conditions as well as the films that were annealed in various environments. Oxygen-annealed films displayed a sequential transition from ferromagnetism to diamagnetism as a function of the annealing temperature. An increase in the green band intensity has been observed in oxygen-annealed ZnO films. Reversible switching of room-temperature ferromagnetism and n-type conductivity have been demonstrated by oxygen and vacuum annealing. Electron paramagnetic resonance data were found to be in agreement with the results of magnetization and conductivity measurements. Possibility of external ferromagnetic impurity as the origin of the unconventional room temperature ferromagnetism in these films has been ruled out by secondary ion mass spectrometer and electron energy loss spectroscopy studies. Correlation between structural, electrical, optical, and magnetic properties has been established in terms of defects and defect complexes. Taken together, our data indicate that the ferromagnetic order in ZnO matrix might be defect-mediated.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mal, Siddhartha and Nori, Sudhakar and Jin, Chunming and Narayan, J. and Nellutla, S. and Smirnov, A. I. and Prater, J. T.}, year={2010}, month={Oct}, pages={073510} }
 @article{yang_jin_zhou_narayan_narayan_2010, title={Role of twin boundaries in semiconductor to metal transition characteristics of VO2 films}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3481075}, DOI={10.1063/1.3481075}, abstractNote={Epitaxial (002) VO2 films were grown on c-sapphire with Ga:ZnO and ZnO buffer layers. We investigated the influence of twin boundaries on the semiconductor-to-metal transition (SMT) characteristics of VO2, when current flows parallel and perpendicular to the twin boundaries. The structure of the twin boundary was kept the same for these two configurations. The hysteresis in SMT characteristics is considerably reduced when current flows parallel to the boundaries compared to that in the normal direction of the boundaries. We present a model to explain these observations and discuss the role of these boundaries on the SMT characteristics, and the importance of grain boundary engineering in the design of VO2 based devices.}, number={7}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Yang, Tsung-Han and Jin, Chunming and Zhou, Honghui and Narayan, Roger J. and Narayan, J.}, year={2010}, month={Aug}, pages={072101} }
 @article{yang_aggarwal_gupta_zhou_narayan_narayan_2010, title={Semiconductor-metal transition characteristics of VO2 thin films grown on c- and r-sapphire substrates}, volume={107}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3327241}, DOI={10.1063/1.3327241}, abstractNote={We have made a comparative study of epitaxial growth of VO2 thin films on c-cut (0001) and r-cut (11¯02) sapphire substrates, and the semiconductor to metal transition (SMT) characteristics of these films have been correlated with their structural details. On c-sapphire, VO2 grows epitaxially in (002) orientation. These (002) oriented VO2 films have 60° twin boundaries due to three equivalent in-plane orientations. The epitaxial VO2 films on r-sapphire consisted of two orientations, namely (200) and (2¯11). The coexistence of these two orientations of VO2 has been explained on the basis of similarity of atomic arrangements in (200) and (2¯11) planes. The thermal hysteresis (ΔH), sharpness of the transition (ΔT), and the transition temperature for VO2 films on c-sapphire were found to be 4.8, 8.5, and 72.6 °C, respectively, which were higher than the corresponding values of 3.3, 5.4, and 60.3 °C for films on r-sapphire. The SMT temperature for VO2 films on c-sapphire was close to the bulk value of 68.0 °C. The significant decrease in transition temperature to 60.3 °C for VO2 films on r-sapphire has been attributed to the compressive strain along [002] direction of VO2.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Yang, Tsung-Han and Aggarwal, Ravi and Gupta, Alok and Zhou, Honghui and Narayan, Roger J. and Narayan, J.}, year={2010}, month={Mar}, pages={053514} }
 @article{aggarwal_zhou_jin_narayan_narayan_2010, title={Semipolar r-plane ZnO films on Si(100) substrates: Thin film epitaxy and optical properties}, volume={107}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3406260}, DOI={10.1063/1.3406260}, abstractNote={We report heteroepitaxial growth of (101¯2) oriented (r-plane) ZnO films on Si(100) substrates. The films were grown by pulsed laser deposition and integration of ZnO with silicon was achieved using a tetragonal yttria stabilized zirconia (YSZ) buffer layer. It was observed that ZnO films grown at temperatures in the range of 700–750 °C with relatively high oxygen pressure (∼70 mTorr) were (101¯2) oriented. ZnO films deposited with lower oxygen pressures were found to be purely (0002) orientated. Experiments carried out to elucidate the role of oxygen pressure indicated that the crystallographic orientation of ZnO depends on the nature of atomic termination of YSZ layer. It has been proposed that crystallographic orientation of ZnO is controlled by chemical free energy associated with ZnO-YSZ interface. Detailed x-ray diffraction and transmission electron microscopy studies showed existence of four types of in-plane domains in r-plane ZnO films. Optical characterization demonstrated that photoluminescence of r-plane ZnO films was superior to that of c-plane ZnO films grown under similar conditions.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Aggarwal, Ravi and Zhou, Honghui and Jin, Chunming and Narayan, J. and Narayan, Roger J.}, year={2010}, month={Jun}, pages={113530} }
 @article{yang_nori_zhou_narayan_2009, title={Defect-mediated room temperature ferromagnetism in vanadium dioxide thin films}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3224202}, DOI={10.1063/1.3224202}, abstractNote={High quality epitaxial undoped vanadium oxide (VO2) thin films on c-plane sapphire (0001) substrate have been grown using pulsed laser deposition technique. The as-grown films exhibited excellent structural and transport properties without requiring further annealing treatments for these oxygen-deficient oxide films. The epitaxial growth has been achieved via domain matching epitaxy, where matching of integral multiples of planes occurs across the film-substrate interface. The magnetic properties of vanadium oxide (VO2) films investigated at different temperatures in the range of 10–360 K showed significant magnetic hysteresis as well as saturation of the magnetic moment. The origin of ferromagnetic properties with an estimated Curie temperature above 500 K is discussed in the absence of magnetic impurities in VO2 thin films as determined by x-ray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Yang, Tsung-Han and Nori, Sudhakar and Zhou, Honghui and Narayan, Jagdish}, year={2009}, month={Sep}, pages={102506} }
 @article{yang_huang_wu_chen_gan_yeh_narayan_2009, title={Effect of annealing on atomic ordering of amorphous ZrTaTiNbSi alloy}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3273387}, DOI={10.1063/1.3273387}, abstractNote={In this letter, we have reported on initial stages of atomic ordering in ZrTaTiNbSi amorphous films during annealing. The atomic ordering and structure evolution were studied in Zr17Ta16Ti19Nb22Si26 amorphous films as a function of annealing temperature in the temperature range from 473 to 1173 K. Up to annealing temperature of 1173 K, the films retained amorphous structure, but the degree of disorder is increased with the increase in temperature. The formation of Si–M covalent bonds, which contributed to the local atomic arrangement, occurred in the initial stages of ordering. The bonding reactions between Si and other metal species explain the anomalous structural changes which were observed in x-ray diffraction and transmission electron microscopy. We discuss the stages of phase transformation for amorphous films as a function of annealing temperature. From these results, we propose that annealing leads to formation of random Si–M4 tetrahedron, and two observed rings, a first and second in the electron diffraction patterns compared to M–M and Si–M bond length, respectively.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Yang, Tsung-Han and Huang, Rong-Tang and Wu, Cheng-An and Chen, Fu-Rong and Gan, Jon-Yiew and Yeh, Jien-Wei and Narayan, Jagdish}, year={2009}, month={Dec}, pages={241905} }
 @article{zhu_narayan_hirth_mahajan_wu_liao_2009, title={Formation of single and multiple deformation twins in nanocrystalline fcc metals}, volume={57}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2009.04.020}, abstractNote={Deformation twins are often observed to meet each other to form multi-fold twins in nanostructured face-centered cubic (fcc) metals. Here we propose two types of mechanism for the nucleation and growth of four different single and multiple twins. These mechanisms provide continuous generation of twinning partials for the growth of the twins after nucleation. A relatively high stress or high strain rate is needed to activate these mechanisms, making them more prevalent in nanocrystalline materials than in their coarse-grained counterparts. Experimental observations that support the proposed mechanisms are presented.}, number={13}, journal={ACTA MATERIALIA}, author={Zhu, Y. T. and Narayan, J. and Hirth, J. P. and Mahajan, S. and Wu, X. L. and Liao, X. Z.}, year={2009}, month={Aug}, pages={3763–3770} }
 @article{gupta_narayan_kumar_2009, title={Magnetic Properties of Self-Assembled Ni Nanoparticles in Two Dimensional Structures}, volume={9}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2009.214}, abstractNote={A pulsed laser deposition technique has been used to synthesize a uniform distribution of Ni nanoparticles of controllable size in Al2O3 thin film matrix. The ability to control particle size in confined layers provides a very convenient means to tune the magnetic properties from superparamagnetic to ferromagnetic. The coercivity of these particles was measured at various temperatures as a function of particle size. The results indicate that the magnetic transition from single- to multi-domain region occurs at a larger particle size at higher temperature than at lower temperature. Stronger magnetic interaction among particles at lower temperatures is believed to lead to the formation of smaller sized domains for any given particle size in order to minimize the interaction energy.}, number={6}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Gupta, A. and Narayan, J. and Kumar, Dhananjay}, year={2009}, month={Jun}, pages={3993–3996} }
 @article{aggarwal_nori_jin_pant_trichy_kumar_narayan_narayan_2009, title={Magnetic properties and their dependence on deposition parameters of Co/Al2O3 multilayers grown by pulsed laser deposition}, volume={57}, ISSN={["1359-6454"]}, DOI={10.1016/j.actamat.2009.01.018}, abstractNote={Co/Al2O3 multilayered thin films were grown on Si (111) substrates by pulsed laser deposition (PLD) at temperatures from room temperature (RT) to 600 °C. The Co/Al2O3 multilayered thin film grown at RT contains continuous cobalt layers in alumina matrices, with no evidence of island formation. On the other hand, cobalt showed a tendency to form islands in alumina matrices for growth temperatures in the range of 300–600 °C. All the Co/Al2O3 multilayered thin films showed ferromagnetic behavior up to RT. It was observed that variations in the deposition parameters can significantly influence the magnetic properties of Co/Al2O3 multilayers. Depending on the temperature and pulse rate, RT coercivities in the 50–300 Oe range were observed. Films deposited at 600 °C using a laser pulse rate of 10 Hz exhibited a decrease of coercivity with increasing measurement temperature. On the other hand, films deposited at 600 °C using a reduced pulse rate of 2 Hz demonstrated an “anomalous” relationship between low-temperature coercivity and temperature. In these films, coercivity exhibited a weak tendency to increase with temperature. Squareness (Mr/Ms) of the hysteresis loops and its dependence on the temperature was also shown to be strongly affected by the deposition parameters. These observations have been rationalized on the basis of two competing magnetic anisotropies that act along different directions in the material.}, number={6}, journal={ACTA MATERIALIA}, author={Aggarwal, Ravi and Nori, Sudhakar and Jin, Chunming and Pant, Punam and Trichy, Gopinath R. and Kumar, Dhananjay and Narayan, J. and Narayan, Roger J.}, year={2009}, month={Apr}, pages={2040–2046} }
 @article{dutta_gupta_bhosle_narayan_2009, title={MoOx modified ZnGaO based transparent conducting oxides}, volume={105}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3078812}, DOI={10.1063/1.3078812}, abstractNote={We report here the growth of high work function bilayered structures of thin MoOx (2.0<x<2.75) layer (few nanometers) on Zn0.95Ga0.05O films by pulsed laser deposition (PLD) on glass and sapphire substrates for transparent electrode applications. It was found that the films were highly textured along [0001] direction. The crystalline quality of the films deposited at different substrate temperatures was investigated by x-ray diffraction, transmission electron microscopy (TEM) imaging, and selected area diffraction pattern (SAED). In the MoOx layer, molybdenum exists in Mo4+, Mo5+, and Mo6+ oxidation states, and the ratio of (Mo4++Mo5+) to Mo6+ was determined to be ∼2:1. The bilayer films showed good optical transparency (≥80%) and low resistivity of ∼10−4 Ω cm. Different transport behavior of the MoOx/ZnGa0.05O films grown at different Ts (substrate temperature) was observed in temperature-dependent resistivity measurements. The bilayer film at higher Ts showed metallic conductivity behavior down to 113 K. Moreover, a blueshift of the absorption edge in the transmission spectrum was observed with the increase in Ts, indicating an increase in the carrier concentration. It was observed that the ZnGa0.05O films with ultrathin MoOx (∼1–2 nanometers) overlayer showed a higher work function (varying from 4.7 to 5.1 eV) as compared to the single layer ZnGa0.05O film work function (∼4.4 eV). A correlation between the surface work function and MoOx layer thickness is observed. The higher work function of the MoOx overlayer is envisaged to improve the transport of the carriers across the heterojunction in a solid state device, thus resulting an increase in device efficiency.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Dutta, Titas and Gupta, P. and Bhosle, V. and Narayan, J.}, year={2009}, month={Mar}, pages={053704} }
 @inproceedings{narayan_2009, title={New frontier in thin film epitaxy and nanostructured materials}, volume={6}, number={5-6}, booktitle={International Journal of Nanotechnology}, author={Narayan, J.}, year={2009}, pages={493–510} }
 @article{pant_budai_narayan_2010, title={Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation}, volume={58}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2009.10.026}, abstractNote={Using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, we investigated the strain relaxation mechanisms for nonpolar (1 1 −2 0) a-plane ZnO epitaxy on (1 −1 0 2) r-plane sapphire, where the in-plane misfit ranges from −1.5% for the [0 0 0 1]ZnO‖[1 −1 0 −1]sapphire to −18.3% for the [−1 1 0 0]ZnO‖[−1 −1 2 0]sapphire direction. For the large misfit [−1 1 0 0]ZnO direction the misfit strains are fully relaxed at the growth temperature, and only thermal misfit and defect strains, which cannot be relaxed fully by slip dislocations, remain on cooling. For the small misfit direction, lattice misfit is not fully relaxed at the growth temperature. As a result, additive unrelaxed lattice and thermal misfit and defect strains contribute to the measured strain. Our X-ray diffraction measurements of lattice parameters show that the anisotropic in-plane biaxial strain leads to a distortion of the hexagonal symmetry of the ZnO basal plane. Based on the anisotropic strain relaxation observed along the orthogonal in-plane [−1 1 0 0] and [0 0 0 1]ZnO stress directions and our HRTEM investigations of the interface, we show that the plastic relaxation occurring in the small misfit direction [0 0 0 1]ZnO by dislocation nucleation is incomplete. These results are consistent with the domain-matching paradigm of a complete strain relaxation for large misfits and a difficulty in relaxing the film strain for small misfits.}, number={3}, journal={ACTA MATERIALIA}, author={Pant, P. and Budai, J. D. and Narayan, J.}, year={2010}, month={Feb}, pages={1097–1103} }
 @article{wei_jin_narayan_narayan_2009, title={Optical and electrical properties of bandgap engineered gallium-doped MgxZn1-xO films}, volume={149}, ISSN={["1879-2766"]}, DOI={10.1016/j.ssc.2009.06.021}, abstractNote={In this study, the optical and electrical properties of heavily gallium-doped MgxZn1−xO films were investigated. Films were epitaxially grown on c-plane sapphire substrates using pulsed laser deposition. Film transparency was shown to be greater than 90% in the visible spectrum. Absorption was shown to be extended to lower wavelengths in films with higher magnesium concentration values. Although transparency in the ultraviolet wavelength range was improved, conductivity was decreased. In MgxZn1−xO films with 0.5 at.% gallium, resistivity was increased from 1.9×10−3Ωcm to 3.62×10−2Ωcm as the magnesium concentration was increased from five atomic percent to fifteen atomic percent. These efforts will facilitate the development of zinc oxide-based ultraviolet–blue light emitting diodes, ultraviolet–blue light laser diodes, and other optoelectronic devices.}, number={39-40}, journal={SOLID STATE COMMUNICATIONS}, author={Wei, Wei and Jin, Chunming and Narayan, Jagdish and Narayan, Roger J.}, year={2009}, month={Oct}, pages={1670–1673} }
 @article{hushur_manghnani_narayan_2009, title={Raman studies of GaN/sapphire thin film heterostructures}, volume={106}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3213370}, DOI={10.1063/1.3213370}, abstractNote={Using Raman spectroscopy, we have studied the optical phonon modes of GaN nucleation layers with the thicknesses of 7 and 45nm, grown on sapphire (0001) substrates by metal organic chemical vapor deposition at low temperatures (500–600°C). These layers consisted of mixed hexagonal and cubic phases. The Raman results from mixed phases were compared with those from pure hexagonal layers which were grown at higher temperatures over 1000°C. The E2H and A1(LO) phonon modes are observed at 548 and 733cm−1 for 45nm thick nucleation layer, while the silent low-frequency B1 mode which is forbidden in good quality hexagonal GaN is observed at 314cm−1. The presence of the strong hexagonal modes for GaN nucleation layers of 45nm thick confirms the crystalline nature of the GaN nucleation layer and dominant hexagonal phase in this mixed cubic-hexagonal nucleation layer. The observed frequencies are shifted with respect to the corresponding A1 and E2 phonon modes in hexagonal GaN. The decrease in mode frequency implies the presence of in-plane tensile strain in these GaN nucleation layers of 45nm thick. The Raman scattering spectra taken from different positions on the sample show similar spectral features, indicating that the GaN nucleation layers of 45nm thick are homogeneous in micron scale.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Hushur, Anwar and Manghnani, Murli H. and Narayan, Jagdish}, year={2009}, month={Sep}, pages={054317} }
 @article{gupta_aggarwal_gupta_dutta_narayan_narayan_2009, title={Semiconductor to metal transition characteristics of VO2 thin films grown epitaxially on Si (001)}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3232241}, DOI={10.1063/1.3232241}, abstractNote={We report semiconductor to metal transition (SMT) characteristics of vanadium dioxide (VO2) grown epitaxially on Si (001) at 500 °C. The epitaxial integration with Si (001) was achieved by using epitaxial tetragonal yttria-stabilized zirconia (YSZ) as an intermediate buffer layer, which was grown in situ. From x-ray (θ-2θ and ϕ-scan) and electron diffraction studies, we established that VO2 and YSZ grow in (020) and (001) orientations, respectively, on Si (001) substrate and epitaxial relationship was established to be “VO2[001] or VO2[100]”//YSZ[110]//Si [100] and VO2(010)//YSZ(001)//Si(001). VO2/YSZ/Si(001) heterostructures showed approximately three orders of magnitude reversible change in resistivity and hysteresis of ∼6 K upon traversing the transition temperature. A 10 °C increase in the SMT temperature of these VO2 films, compared to the value reported for bulk VO2, has been explained on the basis of uniaxial stress along the c-axis, which can stabilize the covalent monoclinic phase up to higher temperatures. A correlation between in-plane orientations of the film and the transition width has also been suggested, which is consistent with our previously published thermodynamic model.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Gupta, A. and Aggarwal, R. and Gupta, P. and Dutta, T. and Narayan, Roger J. and Narayan, J.}, year={2009}, month={Sep}, pages={111915} }
 @article{pant_budai_aggarwal_narayan_narayan_2009, title={Structural characterization of two-step growth of epitaxial ZnO films on sapphire substrates at low temperatures}, volume={42}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/42/10/105409}, DOI={10.1088/0022-3727/42/10/105409}, abstractNote={We have investigated two-step growth of high-quality epitaxial ZnO films, where the first layer—the buffer layer (nucleation layer template)—is grown at a low temperature (230–290 °C) to induce a smooth (two-dimensional) growth. This is followed by growth at a moderate temperature ∼430 °C to form high-quality smooth ZnO layers for device structures. It was possible to reduce the growth temperature to 250–290 °C and obtain a smooth epitaxial template layer on sapphire (0 0 0 1) substrates with surface roughness less than 1 nm. After the high-temperature growth, the film surface undulations (roughness) increased to about 2 nm, but it is still quite smooth. The calculation of c and a lattice parameters by high-resolution x-ray diffraction shows that the a lattice parameter is fully relaxed at the growth temperatures but the c lattice parameter is dependent on the defect concentration in the growing film. A decoupling between a and c lattice parameters of the films is observed, which leads to abnormal Poisson's ratios ranging from 0.08 to 0.54. The decoupling of the lattice parameters is analysed based on growth characteristics and the presence of strain and defects in the grown films. We present our detailed studies on the nature of epitaxy, defects and interfaces by using comprehensive x-ray diffraction and high-resolution TEM studies.}, number={10}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Pant, P and Budai, J D and Aggarwal, R and Narayan, R J and Narayan, J}, year={2009}, month={Apr}, pages={105409} }
 @article{narayan_nori_ramachandran_prater_2009, title={The synthesis and magnetic properties of a nanostructured Ni-MgO system}, volume={61}, ISSN={["1543-1851"]}, DOI={10.1007/s11837-009-0093-8}, number={6}, journal={JOM}, author={Narayan, J. and Nori, Sudhakar and Ramachandran, S. and Prater, J. T.}, year={2009}, month={Jun}, pages={76–81} }
 @article{pant_budai_aggarwal_narayan_narayan_2009, title={Thin film epitaxy and structure property correlations for non-polar ZnO films}, volume={57}, ISSN={["1873-2453"]}, DOI={10.1016/j.actamat.2009.05.031}, abstractNote={Heteroepitaxial growth and strain relaxation were investigated in non-polar a-plane (1 1 −2 0)ZnO films grown on r-plane (1 0 −1 2)sapphire substrates in the temperature range 200–700 °C by pulsed laser deposition. The lattice misfit in the plane of the film for this orientation varied from −1.26% in [0 0 0 1] to −18.52% in the [−1 1 0 0] direction. The alignment of (1 1 −2 0)ZnO planes parallel to (1 0 −1 2)sapphire planes was confirmed by X-ray diffraction θ−2θ scans over the entire temperature range. X-ray ϕ-scans revealed the epitaxial relationship:[0 0 0 1]ZnO‖[−1 1 0 1]sap; [–1 1 0 0]ZnO‖[−1 −1 2 0]sap. Depending on the growth temperature, variations in the structural, optical and electrical properties were observed in the grown films. Room temperature photoluminescence for films grown at 700 °C shows a strong band-edge emission. The ratio of the band-edge emission to green band emission is 135:1, indicating reduced defects and excellent optical quality of the films. The resistivity data for the films grown at 700 °C shows semiconducting behavior with room temperature resistivity of 2.2 × 10−3 Ω-cm.}, number={15}, journal={ACTA MATERIALIA}, author={Pant, P. and Budai, J. D. and Aggarwal, R. and Narayan, Roger J. and Narayan, J.}, year={2009}, month={Sep}, pages={4426–4431} }
 @article{zhu_wu_liao_narayan_mathaudhu_kecskés_2009, title={Twinning partial multiplication at grain boundary in nanocrystalline fcc metals}, volume={95}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3187539}, DOI={10.1063/1.3187539}, abstractNote={Most deformation twins in nanocrystalline face-centered cubic (fcc) metals have been observed to form from grain boundaries. The growth of such twins requires the emission of Shockley partials from the grain boundary on successive slip planes. However, it is statistically improbable for a partial to exist on every slip plane. Here we propose a dislocation reaction and cross-slip mechanism on the grain boundary that would supply a partial on every successive slip plane for twin growth. This mechanism can also produce a twin with macrostrain smaller than that caused by a conventional twin.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Zhu, Y. T. and Wu, X. L. and Liao, X. Z. and Narayan, J. and Mathaudhu, S. N. and Kecskés, L. J.}, year={2009}, month={Jul}, pages={031909} }
 @article{idrobo_pant_narayan_pennycook_pantelides_2008, title={Atomic Investigation of Al2O3/GaN Heterostructures Interfaces using Aberration-Corrected STEM Combined with First-Principles Methods}, volume={14}, ISSN={1431-9276 1435-8115}, url={http://dx.doi.org/10.1017/S1431927608087187}, DOI={10.1017/S1431927608087187}, abstractNote={Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008}, number={S2}, journal={Microscopy and Microanalysis}, publisher={Cambridge University Press (CUP)}, author={Idrobo, JC and Pant, P and Narayan, J and Pennycook, SJ and Pantelides, ST}, year={2008}, month={Aug}, pages={1402–1403} }
 @article{pant_narayan_wushuer_manghnani_2008, title={Comparative Raman and HRTEM Study of Nanostructured GaN Nucleation Layers and Device Layers on Sapphire (0001)}, volume={8}, ISSN={["1533-4880"]}, DOI={10.1166/jnn.2008.334}, abstractNote={Raman spectroscopy in conjunction with high-resolution transmission electron microscopy (HRTEM) has been used to study structural characteristics and strain distribution of the nanostructured GaN nucleation layer (NL) and the GaN device layer on (0001) sapphire substrates used for light-emitting diodes and lasers. Raman peaks corresponding to the cubic and the hexagonal phase of GaN are observed in the Raman spectrum from 15 nm and 45 nm NLs. A comparison of the peak intensities for the cubic and hexagonal phases of GaN in the NLs suggests that the cubic phase is dominant in the 15 nm NL and the hexagonal phase in the 45 nm NL. An increase in the density of stacking faults in the metastable cubic GaN (c-GaN) phase with increasing growth time lowers the system energy as well as locally converts c-GaN phase into hexagonal GaN (h-GaN). It also explains the observation of the more intense peaks of h-GaN in the 45 nm NL compared to c-GaN peaks. For the sample wherein an h-GaN device layer was grown at higher temperatures on the NL, narrow Raman peaks corresponding to only h-GaN were observed, confirming the high-quality of the films. The peak shift of the E2(H)(LO) mode of h-GaN in the NLs and the h-GaN film suggests the presence of a tensile stress in the NL which is attributed to defects such as stacking faults and twins, and a compressive stress in high-temperature grown h-GaN film which is attributed to the thermal-expansion mismatch between the film and the substrate. The peak shifts of the substrate also reveal that during the low temperature growth of the NL the substrate is under a compressive stress which is attributed to defects in the NL and during the high temperature growth of the device layer, there is a tensile strain in the substrate as expected from differences in coefficients of thermal expansion of the film and the substrate during the cooling cycle.}, number={11}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Pant, P. and Narayan, J. and Wushuer, A. and Manghnani, M. H.}, year={2008}, month={Nov}, pages={5985–5992} }
 @article{narayan_nori_pandya_avasthi_smirnov_2008, title={Defect dependent ferromagnetism in MgO doped with Ni and Co}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2977614}, DOI={10.1063/1.2977614}, abstractNote={We have investigated magnetic properties of MgO single crystals doped with Ni and Co impurities, and studied changes in magnetic properties after heavy ion irradiation. These results are compared with doped single-crystal thin films that contain a higher concentration of trapped defects. The as-grown bulk single crystals, which contain a small equilibrium concentration of vacancies, exhibit a perfect paramagnetic behavior throughout the temperature range and magnetic field. By introducing defects either by ion irradiation or by thin film deposition, which have trapped defects, we are able to achieve defect-mediated ferromagnetic ordering.}, number={8}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Narayan, J. and Nori, Sudhakar and Pandya, D. K. and Avasthi, D. K. and Smirnov, A. I.}, year={2008}, month={Aug}, pages={082507} }
 @article{wu_narayan_zhu_2008, title={Deformation twin formed by self-thickening, cross-slip mechanism in nanocrystalline Ni}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2949685}, DOI={10.1063/1.2949685}, abstractNote={We report the observation of a deformation twin formed by a recently proposed self-thickening, cross-slip twinning mechanism. This observation verifies one more twinning mechanism, in addition to those reported before, in nanocrystalline face-centered-cubic metals. In this mechanism, once the first Shockley partial is emitted from a grain boundary, and cross slips onto another slip plane, a deformation twin could nucleate and grow in both the primary and cross-slip planes without requiring the nucleation of additional Shockley partials from the grain boundary.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Wu, X. L. and Narayan, J. and Zhu, Y. T.}, year={2008}, month={Jul}, pages={031910} }
 @article{aggarwal_jin_pant_narayan_narayan_2008, title={Growth of biepitaxial zinc oxide thin films on silicon (100) using yttria-stabilized zirconia buffer layer}, volume={93}, ISSN={["0003-6951"]}, DOI={10.1063/1.3050529}, abstractNote={In this work, an approach for integrating zinc oxide thin films with Si(100) substrates using an epitaxial tetragonal yttria-stabilized zirconia buffer layer is reported. Selected area electron diffraction measurements revealed the following epitaxial relationship: [110]YSZ∥[100]Si and (001)YSZ∥(001)Si. X-ray diffraction studies demonstrated that subsequent growth of the zinc oxide thin film on the yttria-stabilized zirconia buffer layer occurred with the following epitaxial relationship: (0002)ZnO∥(001)YSZ. The full width at half maximum value for the (0002) peak of zinc oxide was small (∼0.16°), which indicated good crystalline quality. Transmission electron microscopy revealed that the zinc oxide thin film grew epitaxially on an yttria-stabilized zirconia buffer layer in two different orientations, where one orientation was rotated by 30° from the other. The orientation relationship in this case was [101¯0]ZnO∥[100]YSZ or [21¯1¯0]ZnO∥[100]YSZ and (0002)ZnO∥(001)YSZ. The biepitaxial growth of the zinc oxide thin film has been explained in the framework of domain matching epitaxy. Optical emission measurements showed a strong excitonic emission peak from the zinc oxide thin film at ∼377 nm. Minimal green band emission in the photoluminescence spectrum indicated that the concentration of point defects was low. Integration of epitaxial zinc oxide thin films with Si(100) substrates is an important step toward developing practical applications of zinc oxide in a variety of optoelectronic devices.}, number={25}, journal={Applied Physics Letters}, author={Aggarwal, Ravi and Jin, Chunming and Pant, Punam and Narayan, Jagdish and Narayan, Roger J.}, year={2008}, month={Dec}, pages={251905} }
 @article{bhosle_narayan_2008, title={Observation of room temperature ferromagnetism in Ga:ZnO: A transition metal free transparent ferromagnetic conductor}, volume={93}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2953705}, DOI={10.1063/1.2953705}, abstractNote={This paper reports our results on room temperature ferromagnetism characteristics in Ga-doped ZnO. The Ga-doped ZnO films were grown epitaxially on (0001) sapphire with Ga concentration up to 5at.%. Detailed x-ray diffraction and high resolution transmission electron microscopy results showed a high-quality epitaxy without the presence of any secondary phases. Magnetic measurements showed characteristic ferromagnetism behavior with room temperature coercivity ∼50Oe, which remained fairly constant with temperature. Upon annealing coercivity disappeared with typical diamagnetic characteristics of ZnO. The x-ray photoelectron spectroscopy and electrical measurements as function of annealing showed a critical role of vacancies and Ga-vacancy complexes to be critical for the observed ferromagnetic behavior.}, number={2}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Bhosle, V. and Narayan, J.}, year={2008}, month={Jul}, pages={021912} }
 @article{haverkamp_bourham_du_narayan_2008, title={Plasma instabilities in magnetically assisted pulsed laser deposition}, volume={41}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/41/11/115206}, DOI={10.1088/0022-3727/41/11/115206}, abstractNote={The laser ablation of a carbon target in a transverse magnetic field is studied using a quadruple Langmuir probe. Ion saturation signals indicate the presence of wavelike behaviour not found in field-free laser ablation of carbon. Results are discussed in terms of the lower-hybrid drift instability and the electron–ion hybrid instability. The results are found to be most consistent with the electron–ion hybrid instability.}, number={11}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Haverkamp, J D and Bourham, M A and Du, S and Narayan, J}, year={2008}, month={May}, pages={115206} }
 @article{haverkamp_bourham_du_narayan_2008, title={Plasma plume dynamics in magnetically assisted pulsed laser deposition}, volume={42}, ISSN={0022-3727 1361-6463}, url={http://dx.doi.org/10.1088/0022-3727/42/2/025201}, DOI={10.1088/0022-3727/42/2/025201}, abstractNote={The expansion of a laser produced plasma perpendicular to a magnetic field is studied with a quadruple Langmuir probe and a B-dot probe. In regions where the kinetic beta is less than one, we find plume deceleration and weak displacement of the magnetic field. As the plume expands into regions of weak magnetic field, plume deceleration stops and the displacement of the magnetic field is large. The diffusion time of the magnetic field lines was consistent with anomalously large resistivity driven by the presence of an instability. Electron temperatures are larger than in the field-free case due to Ohmic heating mediated by the anomalously large resistivity.}, number={2}, journal={Journal of Physics D: Applied Physics}, publisher={IOP Publishing}, author={Haverkamp, J D and Bourham, M A and Du, S and Narayan, J}, year={2008}, month={Dec}, pages={025201} }
 @article{narayan_zhu_2008, title={Self-thickening, cross-slip deformation twinning model}, volume={92}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2911735}, DOI={10.1063/1.2911735}, abstractNote={We propose a cross-slip deformation twinning model based upon our experimental in situ deformation of Cu–Ge alloys using a transmission electron microscope. During the deformation, Shockley partials are emitted from the grain boundaries, which encounter an obstacle within the grain and split to nucleate deformation twins in the cross slip as well as primary planes. Upon further deformation a thickening process for twins is directly observed. The proposed model provides a dislocation mechanism for the observed simultaneous twin thickening in both the cross-slip and primary planes. The role of the proposed mechanism in the deformation of nanocrystalline materials is discussed.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Narayan, J. and Zhu, Y. T.}, year={2008}, month={Apr}, pages={151908} }
 @article{trichy_chakraborti_narayan_prater_2008, title={Structure-magnetic property correlations in the epitaxial FePt system}, volume={92}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2883933}, DOI={10.1063/1.2883933}, abstractNote={We present findings on the effect of microstructure on magnetic properties of the epitaxial FePt system. Epitaxial c-axis oriented FePt was synthesized on Si (100) using TiN as a template buffer. The microstructure was progressively varied from a 9nm nanoparticle system to a 30nm thick continuous thin film. We found that individual nanoparticles showed higher coercivity than the continuous thin film. Within the nanoparticle regime, coercivity increased with increasing particle size. The highest coercivity of 13500Oe was realized for a beadlike microstructure, when the individual nanoparticles just begin to merge to form a continuous thin film.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Trichy, G. R. and Chakraborti, D. and Narayan, J. and Prater, J. T.}, year={2008}, month={Mar}, pages={102504} }
 @article{darling_guduru_reynolds_bhosle_chan_scattergood_koch_narayan_aboelfotoh_2008, title={Thermal stability, mechanical and electrical properties of nanocrystalline Cu3Ge}, volume={16}, ISSN={0966-9795}, url={http://dx.doi.org/10.1016/j.intermet.2007.11.005}, DOI={10.1016/j.intermet.2007.11.005}, abstractNote={The intermetallic ɛ1 compound Cu3Ge was produced through a mechanical alloying procedure that enables the formation of a nanograined microstructure. There is a dependence of grain size (20–11 nm) on milling conditions. The microstructure remained very stable even at temperatures up to 500 °C for 5 h which is a minimum of 76% of the melting temperature. The materials produced by these methods were in the form of powders with particle size ranging from 200 nm to 10 μm. The morphology of the particles varied with the largest being rough and irregular and the smallest being spherical. Preliminary resistivity measurements showed low resistivity, 8.8 μΩ cm, which is comparable to that previously reported for thin films with grain sizes thousands of times larger. Nanoindentation was also performed, yielding an elastic modulus of ∼110 GPa.}, number={3}, journal={Intermetallics}, publisher={Elsevier BV}, author={Darling, Kris A. and Guduru, R.K. and Reynolds, C. Lewis, Jr and Bhosle, Vikram M. and Chan, Ryan N. and Scattergood, Ronald O. and Koch, Carl C. and Narayan, J. and Aboelfotoh, M.O.}, year={2008}, month={Mar}, pages={378–383} }
 @article{bhosle_prater_narayan_2007, title={Anisotropic magnetic properties in [110] oriented epitaxial La0.7Sr0.3MnO3 films on (0001) sapphire}, volume={102}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2751118}, DOI={10.1063/1.2751118}, abstractNote={We have grown virtually strain-free [110] oriented epitaxial La0.7Sr0.3MnO3 films on (0001) sapphire and investigated orientation dependent magnetic properties to study magnetic anisotropy in detail. Measurements of angular dependence of magnetization in the plane of LSMO films reveal that the easy axis lies along [002], whereas [1¯10] acts as the hard axis. We also show that there is no out-of-plane anisotropy, when the magnetization is measured along the equivalent directions, which suggests uniaxial magnetic anisotropy. The observation of uniaxial magnetic anisotropy in the LSMO films deposited on sapphire is attributed to magnetocrystalline anisotropy and is substantiated with detailed transmission electron microscopy analysis and theoretical correlations.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhosle, V. and Prater, J. T. and Narayan, J.}, year={2007}, month={Jul}, pages={013527} }
 @article{chakraborti_trichy_narayan_prater_kumar_2007, title={Effect of Al doping on the magnetic and electrical properties of Zn(Cu)O based diluted magnetic semiconductors}, volume={102}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2817824}, DOI={10.1063/1.2817824}, abstractNote={The effect of Al doping on the magnetic properties of Zn(Cu)O based dilute magnetic semiconducting thin films has been systematically investigated. Epitaxial thin films have been deposited onto sapphire c-plane single crystals using pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy studies show that the Zn(Cu,Al)O films are epitaxially grown onto (0001) sapphire substrates with a 30°/90° rotation in the basal plane. The large lattice misfit of the order of 16% is accommodated by matching integral multiples of lattice and substrate planes. In these large mismatch systems, the resulting films are fully relaxed following deposition of the first complete monolayer of ZnO (consistent with a critical thickness that is less than one monolayer). Magnetic hysteresis measurements indicate that the pure Zn(Cu)O thin films are ferromagnetic at room temperature. Doping with up to 5% Al (n type) does not significantly affect the ferromagnetism even though it results in an increase in carrier densities of more than 3 orders of magnitude, rising from 1×1017 to 1.5×1020 cm−3. However, for Al additions above 5%, a drop in net magnetization is observed. Annealing the films in an oxygen atmosphere at 600 °C also resulted in a dramatic drop in magnetic moment of the samples. These results strongly suggest that carrier induced exchange is not directly responsible for the magnetic properties of these materials. Rather, a defect mediated exchange mechanism needs to be invoked for this system.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Chakraborti, D. and Trichy, G. and Narayan, J. and Prater, J. T. and Kumar, D.}, year={2007}, month={Dec}, pages={113908} }
 @article{trichy_chakraborti_narayan_prater_2007, title={Epitaxial FePt thin films and nanodots integrated with Si (1 0 0)}, volume={40}, DOI={10.1088/0022-3727/40/23/003}, abstractNote={We present findings on the synthesis and processing of various FePt nanostructures using pulsed laser deposition. FePt was deposited as (a) continuous thin films, (b) single layered nanodots and (c) multi-layered nanodots. Integration of these FePt nanostructures with Si (1 0 0) was achieved by using epitaxial TiN as a template buffer layer. Epitaxy and L10 order in the FePt structures were investigated in detail by x-ray diffraction and transmission electron microscopy techniques. Remarkably, we achieved ⟨0 0 1⟩ c-axis growth orientation and L10 ordering at a low processing temperature of 500 °C. The following epitaxial relationship was obtained in the FePt structures: FePt (0 0 1) ⟨0 0 1⟩ ∥ TiN (1 0 0) ⟨0 0 1⟩ ∥ Si (1 0 0) ⟨0 0 1⟩. The 9.5% misfit strain between FePt and TiN is relaxed by domain matching epitaxy where 10/19 and 11/10 domains alternate across the interface. The composition of the nanostructures was determined by Rutherford backscattering and was found to be Fe41Pt59. The magnetic properties of each of the three nanostructured systems were studied individually and then compared to evaluate them as potential information storage media. Room temperature perpendicular coercivity of 3200 Oe for the single layered FePt nanodot sample was much improved when compared with the continuous epitaxial FePt film sample showing a coercivity of 2250 Oe. In the FePt nanodot system, each nanodot acts as a single domain and assuming one bit of information is stored in each nanodot, magnetic storage density can exceed one terabit per square inch, corresponding to 250 million pages of information per chip.}, number={23}, journal={Journal of Physics D: Applied Physics}, author={Trichy, G.R. and Chakraborti, D. and Narayan, J. and Prater, J.T.}, year={2007}, month={Nov}, pages={7273–7280} }
 @article{bhosle_narayan_2007, title={Epitaxial growth and magnetic properties of La0.7Sr0.3MnO3 films on (0001) sapphire}, volume={90}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2472537}, DOI={10.1063/1.2472537}, abstractNote={In this letter the authors report the growth of (110) oriented La0.7Sr0.3MnO3 films on (0001) single-crystal sapphire substrate. Growth of La0.7Sr0.3MnO3 (LSMO) films with a fixed orientation was achieved by carefully controlling the deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the sapphire substrate ((110)f‖(0002)s, (1¯10)f‖(01¯10)s, (002)f‖(2¯110)s), has been explained via domain matching epitaxy, where there is perfect matching in one direction and 19% planar misfit in the perpendicular direction. LSMO films showed interesting magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [002]f as strong and [1¯10]f as weak magnetization directions.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Bhosle, V. and Narayan, J.}, year={2007}, month={Mar}, pages={101903} }
 @article{bhosle_prater_yang_burk_forrest_narayan_2007, title={Gallium-doped zinc oxide films as transparent electrodes for organic solar cell applications}, volume={102}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2750410}, DOI={10.1063/1.2750410}, abstractNote={We report microstructural characteristics and properties of gallium-doped ZnO films deposited on glass by pulsed laser deposition. The Zn0.95Ga0.05O film deposited at 200 °C and 1×10−3 Torr showed predominant ⟨0001⟩ orientation with a metallic behavior and a resistivity of 2×10−4 Ω cm at room temperature. Low resistivity of the ZnGaO films has been explained in terms of optimal combination of carrier concentration and minimized scattering, and is correlated with the microstructure and the deposition parameters. Power conversion efficiency comparable to indium tin oxide-based devices (1.25±0.05%) is achieved on a Zn0.95Ga0.05O∕Cu-phthalocyanine∕C60 double-heterojunction solar cell.}, number={2}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhosle, V. and Prater, J. T. and Yang, Fan and Burk, D. and Forrest, S. R. and Narayan, J.}, year={2007}, month={Jul}, pages={023501} }
 @article{trichy_chakraborti_narayan_zhou_2007, title={Growth, characterization, and magnetic properties of FePt nanodots on Si (100)}, volume={102}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2761832}, DOI={10.1063/1.2761832}, abstractNote={We report on the pulsed laser deposition of epitaxial FePt nanodots onto Si (100) substrates using TiN as a template buffer. X-ray diffraction studies show that the FePt nanodots are primarily oriented along the [001] direction and show L10 ordering with order parameter (S) equal to 0.75. The composition of the nanodots was determined by Rutherford backscattering and was found to be Fe41Pt59. Cross sectional transmission electron microscopy revealed the following epitaxial relationship: FePt(001)⟨001⟩∥TiN(100)⟨001⟩∥Si(100)⟨001⟩. Plan view transmission electron microscopy analysis showed that the FePt nanodots are well separated and have an average size of 18nm. Selected area electron diffraction patterns along the ⟨110⟩ and ⟨001⟩ zone axes were analyzed to study the L10 order in the FePt nanodots. Room temperature magnetic hysteresis measurements showed that the islands are predominantly magnetized in the perpendicular direction with higher coercivity (Hc⊥=3200Oe) as compared to the parallel direction (Hc‖=1000Oe). These values of coercivity at room temperature are highly desirable for information storage applications.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Trichy, G. R. and Chakraborti, D. and Narayan, J. and Zhou, H.}, year={2007}, month={Aug}, pages={033901} }
 @article{venkateshan_singh_poole_harriss_senter_teague_narayan_2007, title={High- gate dielectrics with ultra-low leakage current for sub-45 nm CMOS}, volume={43}, ISSN={0013-5194}, url={http://dx.doi.org/10.1049/el:20072178}, DOI={10.1049/el:20072178}, abstractNote={The results of a new method of high-κ dielectric formation are reported. For effective oxide thickness of 0.39 nm, the leakage current density of metal-high-κ-silicon structure is about 1×10−12 A/cm2 for gate voltage from +3 to −3 V. The descriptive statistics and process variation data presented demonstrate that the process is robust and manufacturing tools can be developed without any fundamental barrier.}, number={21}, journal={Electronics Letters}, publisher={Institution of Engineering and Technology (IET)}, author={Venkateshan, A. and Singh, R. and Poole, K.F. and Harriss, J. and Senter, H. and Teague, R. and Narayan, J.}, year={2007}, pages={1130} }
 @article{venkateshan_singh_poole_harriss_senter_teague_narayan_2007, title={High-kappa gate dielectrics with ultra-low leakage current for sub-45 nm CMOS}, volume={43}, DOI={10.1049/e1:20072178}, number={21}, journal={Electronics Letters}, author={Venkateshan, A. and Singh, R. and Poole, K. F. and Harriss, J. and Senter, H. and Teague, R. and Narayan, Jagdish}, year={2007}, pages={1130–1132} }
 @article{ramachandran_narayan_prater_2007, title={Magnetic properties of Ni-doped MgO diluted magnetic insulators Author(s}, volume={90}, ISSN={["1077-3118"]}, DOI={10.1063/1.2717574}, abstractNote={Magnesium oxide doped with Ni has been studied in two different forms: one in which the Ni ions are incorporated into the substitutional sites and the other in which Ni is present both in substitutional sites and in the form of metallic Ni precipitates embedded in the MgO matrix. Magnetic properties of these materials have been studied and correlated with the microstructural properties. There is a significant difference in the magnetic properties between the two forms. From these studies the authors envisage that a diluted magnetic insulator will be paramagnetic in the absence of intrinsic defects such as vacancies and interstitials. MgO is a good system to perform the present studies as it can be synthesized as a high quality crystal devoid of defects to a high degree. Moreover, the magnetic properties of the Ni precipitates can be used to compare the results when a diluted magnetic semiconductor material is not fully devoid of nanoclusters/precipitates and secondary phases.}, number={13}, journal={Applied Physics Letters}, author={Ramachandran, S. and Narayan, J. and Prater, J.T.}, year={2007}, month={Mar}, pages={132511} }
 @article{ramachandran_prater_sudhakar_kumar_narayan_2008, title={Magnetic properties of epitaxial oxide heterostructures}, volume={145}, ISSN={["1879-2766"]}, DOI={10.1016/j.ssc.2007.10.005}, abstractNote={Diluted Magnetic Semiconductors (DMS) are of great interest as injection sources for spin-polarized currents into semiconductors. Epitaxial devices have been synthesized with an intermediate spacer layer of the same semiconductor (zinc oxide, ZnO) used to produce the DMS material (ZnCoO) ensuring a homoepitaxial junction to help reduce the interface states and conduction mismatch. We observe a large magnetoresistance of about 32% in the devices at low temperatures. The present work suggests that spin polarized transport could be achieved with DMS materials acting as the source of injected spins into a non-magnetic host.}, number={1-2}, journal={SOLID STATE COMMUNICATIONS}, author={Ramachandran, S. and Prater, J. T. and Sudhakar, N. and Kumar, D. and Narayan, J.}, year={2008}, month={Jan}, pages={18–22} }
 @article{chakraborti_ramachandran_trichy_narayan_prater_2007, title={Magnetic, electrical, and microstructural characterization of ZnO thin films codoped with Co and Cu}, volume={101}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2711082}, DOI={10.1063/1.2711082}, abstractNote={Here we report on systematic studies of the epitaxial growth and properties of Co and Cu codoped ZnO thin films deposited onto sapphire c-plane single crystals using pulsed-laser deposition. The films display ferromagnetic behavior at room temperature. Detailed atomic scale characterization rules out the presence of clusters and secondary phases as the source of ferromagnetism. Optical measurements and x-ray photoelectron spectroscopy confirm the direct substitution of dopant atoms into Zn lattice sites. At low concentrations of Cu (∼5%) the magnetic moment of Zn1−(0.05+x)Co0.05CuxO materials appears to be additive. At higher concentrations of Cu the net magnetic moment per atom drops off sharply and seems to be relatively insensitive to the Co content. There is a dramatic increase in resistivity of the Co-doped films that accompanies Cu doping. Yet, this change of resistivity does not affect the magnetic moment, suggesting that free carrier mediated mechanism is not a feasible explanation for ferromagnetism in these films. The known presence of high oxygen vacancies in these films does allow for possible defect mediated mechanisms (e.g., bound magnetic polarons) for mediating exchange coupling of the dopant (Co,Cu) ions resulting in room temperature ferromagnetism.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Chakraborti, D. and Ramachandran, S. and Trichy, G. and Narayan, J. and Prater, J. T.}, year={2007}, month={Mar}, pages={053918} }
 @article{narayan_pant_wei_narayan_budai_2007, title={Nanostructured GaN nucleation layer for light-emitting diodes}, volume={7}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2007.670}, abstractNote={This paper addresses the formation of nanostructured gallium nitride nucleation (NL) or initial layer (IL), which is necessary to obtain a smooth surface morphology and reduce defects in h-GaN layers for light-emitting diodes and lasers. From detailed X-ray and HR-TEM studies, researchers determined that this layer consists of nanostructured grains with average grain size of 25 nm, which are separated by small-angle grain boundaries (with misorientation approximately 1 degrees), known as subgrain boundaries. Thus NL is considered to be single-crystal layer with mosaicity of about 1 degrees. These nc grains are mostly faulted cubic GaN (c-GaN) and a small fraction of unfaulted c-GaN. This unfaulted Zinc-blende c-GaN, which is considered a nonequilibrium phase, often appears as embedded or occluded within the faulted c-GaN. The NL layer contained in-plane tensile strain, presumably arising from defects due to island coalescence during Volmer-Weber growth. The 10L X-ray scans showed c-GaN fraction to be over 63% and the rest h-GaN. The NL layer grows epitaxially with the (0001) sapphire substrate by domain matching epitaxy, and this epitaxial relationship is remarkably maintained when c-GaN converts into h-GaN during high-temperature growth.}, number={8}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Narayan, J. and Pant, P. and Wei, W. and Narayan, R. J. and Budai, J. D.}, year={2007}, month={Aug}, pages={2719–2725} }
 @article{sudhakar_rajeev_tiwari_narayan_2007, title={Room temperature ferromagnetism and magnetotransport properties of the layered manganite system La1.2Ba1.8Mn2-xRuxO7 (0 <= x <= 1-0)}, volume={142}, ISSN={["1879-2766"]}, DOI={10.1016/j.ssc.2007.03.041}, abstractNote={The dc magnetization and ac susceptibility measurements on two dimensional layered manganite La1.2Ba1.8Mn2O7 samples reveal the occurrence of ferromagnetism above room temperature with ferromagnetic (FM) to paramagnetic (PM) transitions at 338 K. The bifurcation temperatures shown by the zero-field cooled (ZFC) and field cooled (FC) dc magnetization curves at high temperatures shift towards lower temperatures as the applied field is increased from 100 to 2500 Oe. The data are suggestive of a large magnetic anisotropy due to the strong competing ferromagnetic and antiferromagnetic interactions resulting in a spin-glass-like state. Ru doping is found to enhance the ferromagnetism and metallicity of the system in a remarkable way. The magnetoresistance (MR) values obtained are very high and about 40% even at 260 K for the undoped sample.}, number={9}, journal={SOLID STATE COMMUNICATIONS}, author={Sudhakar, N. and Rajeev, K. P. and Tiwari, A. and Narayan, J.}, year={2007}, month={Jun}, pages={519–524} }
 @article{chakraborti_narayan_prater_2007, title={Room temperature ferromagnetism in Zn1−xCuxO thin films}, volume={90}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2450652}, DOI={10.1063/1.2450652}, abstractNote={Here the authors report systematic studies on the epitaxial growth and properties of Zn1−xCuxO (x=0.02–0.1) thin films deposited onto sapphire c-plane single crystals using pulsed-laser deposition. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) were employed to study the epitaxial relations of Zn1−xCuxO with the substrate, and x-ray photoelectron spectroscopy was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature ferromagnetism was observed in the Zn1−xCuxO films with magnetic moment per Cu atom decreasing with an increasing Cu content. The presence of any magnetic phase was ruled out using HRTEM. Thus, the ferromagnetism was attributed to Cu ions substituted into the ZnO lattice.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Chakraborti, D. and Narayan, J. and Prater, J. T.}, year={2007}, month={Feb}, pages={062504} }
 @article{sudhakar_ningthoujam_rajeev_gajbhiye_narayan_2007, title={Structural, magnetic, and electron transport studies on nanocrystalline layered manganite La1.2Ba1.8Mn2O7 system}, volume={7}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2007.405}, abstractNote={The structure property relationship for Ru doped La1.2Ba1.8Mn2-RuxO7 system has been studied systematically. The system crystallizes in the single-phase tetragonal structure with space group of 14/mmm. The unit cell volume is found to increase with Ru doping. The sheet type microstructure could be seen in this system, which is important for anisotropic nature of layered structure. The crystallite size is found to be 25 nm indicating nanocrystalline nature of the system. Ferromagnetic to paramagnetic (Tc) transition above the room temperature is observed in all except the highest doped Ru (x = 1.0) where the Tc is 254 K using a.c. susceptibility measurement. The large values of magnetoresistance for the x = 0.0 sample at 10 K is found to be 57% and 64% at applied fields of 5 and 10 T, respectively.}, number={3}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Sudhakar, N. and Ningthoujam, R. S. and Rajeev, K. P. and Gajbhiye, N. S. and Narayan, J.}, year={2007}, month={Mar}, pages={965–969} }
 @article{chakraborti_trichy_prater_narayan_2007, title={The effect of oxygen annealing on ZnO : Cu and ZnO :(Cu,Al) diluted magnetic semiconductors}, volume={40}, ISSN={["1361-6463"]}, DOI={10.1088/0022-3727/40/24/002}, abstractNote={Here we report a systematic study of magnetic, electronic and microstructural properties of Cu-doped and Cu and Al codoped ZnO thin films, grown epitaxially on a (0 0 0 1) sapphire substrate by the pulsed laser deposition technique. The films were annealed in oxygen at high temperature (600 °C) and their properties were compared with the as deposited films in order to study the role of defects like oxygen vacancies on the ferromagnetic properties. The doping of ZnO : Cu specimens with Al increased the carrier concentration by three orders of magnitude (from 1017 to 1020 cm−3) without altering the ferromagnetic ordering. On the other hand, a reduction in oxygen vacancies concentration brought about by high temperature annealing in oxygen had a large detrimental effect on ferromagnetism. These results tend to eliminate a free carrier mediated mechanism and point towards a defect mediated mechanism, such as a bound-magnetic-polaron mediated exchange, as being responsible for stabilizing long-range ferromagnetic ordering in these systems.}, number={24}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Chakraborti, D. and Trichy, G. R. and Prater, J. T. and Narayan, J.}, year={2007}, month={Dec}, pages={7606–7613} }
 @article{narayan_pant_chugh_choi_fan_2006, title={Characteristics of nucleation layer and epitaxy in GaN/sapphire heterostructures}, volume={99}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2178660}, DOI={10.1063/1.2178660}, abstractNote={We present the details of GaN nucleation layer grown on (0001) sapphire substrates below 600°C by metal organic chemical vapor deposition. These films have cubic (c-GaN) zinc blende structure which starts to transform into a hexagonal (h-GaN) wurtzite structure upon annealing around 650°C and above. The films deposited above 700°C by pulsed laser deposition directly on sapphire substrate showed the wurtzite structure. Both c-GaN and h-GaN films grow epitaxially on (0001) sapphire substrates via domain matching epitaxy, where integral multiples of planes match across the film-substrate interface. The c-GaN has the following epitaxial relationship: ⟨111⟩c-GaN‖⟨0001⟩sap, ⟨110⟩c-GaN‖⟨10-10⟩sap, and ⟨211⟩c-GaN‖⟨−2110⟩sap. In terms of planar matching, (220) planes of c-GaN match with (30-30) planes of sapphire, and 1∕3(4¯2¯2¯) planes of c-GaN match with (−2110) planes of sapphire in the perpendicular direction. The transformation from c-GaN into h-GaN involves the transformation of (220) planes of c-GaN into (−2110) planes of h-GaN and 1∕3(422) planes of c-GaN into (30-30) planes of h-GaN, and the epitaxial relationship changes to ⟨0001⟩h-GaN‖⟨0001⟩sap and ⟨−2110⟩h-GaN‖⟨10-10⟩sap. In terms of planar matching epitaxy, (−2110) planes of h-GaN match with (30-30) planes of sapphire, and, in the perpendicular direction, (30-30) planes of h-GaN match with (−2110) planes of sapphire. This epitaxial relationship is known as 30° or 90° rotation. It is interesting to note that relative spacing for c-GaN as well as h-GaN planes remains the same during this transformation because of a(c-GaN)=√2a(h-GaN)=√3c(h-GaN)∕2 equivalence between lattice constants of cubic and hexagonal structures. The transformation from cubic to hexagonal structure can occur via insertion or removal of stacking faults in {111} planes of c-GaN and {0001} planes of h-GaN. The hexagonal structure is preferred as a template for higher-temperature growth, however, the cubic structure, which is a defective hexagonal with stacking faults in alternate layers, can also provide a template for epitaxy. The role of Shockley partials terminating at the island edges and the dislocations associated with subgrain boundaries in the generation of threading dislocations is discussed.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, J. and Pant, Punam and Chugh, A. and Choi, H. and Fan, J. C. C.}, year={2006}, month={Mar}, pages={054313} }
 @article{prater_ramachandran_tiwari_narayan_2006, title={Co-doped ZnO dilute magnetic semiconductor}, volume={35}, ISSN={["0361-5235"]}, DOI={10.1007/BF02692539}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Prater, JT and Ramachandran, S and Tiwari, A and Narayan, J}, year={2006}, month={May}, pages={852–856} }
 @article{narayan_2006, title={Critical size for defects in nanostructured materials}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2220472}, DOI={10.1063/1.2220472}, abstractNote={This paper addresses some of the fundamental issues and critical advantages in reducing the grain size/feature size to the nanoscale regime. We find that as the grain size or feature size is reduced, there is a critical size below which the defect content can be reduced virtually to zero. This critical size for most defects in solid state materials falls in the nanoscale regime. Thus, nanostructured materials offer a unique opportunity to realize the property of a perfect material. However, with this opportunity comes a great challenge in terms of engineering a large fraction of atoms near the surfaces/interfaces. Since the fraction of atoms near the surfaces/interfaces increases inversely with size, this fraction can get closer to unity and determine efficacy of nanostructured materials in terms of efficiency, stability, and reliability of nanostructures. We discuss briefly ways to enhance the stability and reliability of nanostructured systems by controlling the properties of interfaces.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, Jagdish}, year={2006}, month={Aug}, pages={034309} }
 @article{ramachandran_narayan_prater_2006, title={Effect of oxygen annealing on Mn doped ZnO diluted magnetic semiconductors}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2213930}, DOI={10.1063/1.2213930}, abstractNote={We have investigated the properties of Zn1−xMnxO (x=0.01–0.1) thin films grown on c-plane sapphire single crystals by pulsed laser deposition. The electrical, magnetic, optical, and microstructural properties of these thin films have been characterized systematically, with a primary focus on establishing a correlation between magnetic properties and electrical conductivity. We have shown that this system exhibits ferromagnetism at room temperature when in the conducting as-deposited state. However, upon high temperature annealing in excess oxygen, the samples become insulating and exhibit nonferromagnetic behavior at room temperature. Thus, it is possible to tune ferromagnetism in Zn1−xMnxO diluted magnetic semiconductors by controlling the concentrations of oxygen vacancies and substitutional Mn dopants.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Ramachandran, S. and Narayan, J. and Prater, J. T.}, year={2006}, month={Jun}, pages={242503} }
 @article{bhosle_tiwari_narayan_2006, title={Electrical properties of transparent and conducting Ga doped ZnO}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2218466}, DOI={10.1063/1.2218466}, abstractNote={In this paper, we report on the metal-semiconductor transition behavior observed in transparent and conducting ZnO:Ga films grown by pulsed-laser deposition. The electrical resistivity measurements were carried out on ZnO films with varying Ga concentration in the temperature range of 14to300K. The electrical properties were correlated with film structure, and detailed structural characterization was performed using x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. The room-temperature resistivity of these films was found to decrease with Ga concentration up to 5% Ga, and then increase. The lowest value of resistivity (1.4×10−4Ωcm) was found at 5% Ga. Temperature dependent resistivity measurements showed a metal-semiconductor transition, which is rationalized by localization of degenerate electrons. A linear variation of conductivity with T below the transition temperature suggests that the degenerate electrons are in a weak-localization regime. It was also found that the transition temperature is dependent on the Ga concentration and is related to the increase in disorder induced by dopant addition. The results of this research help to understand the additional effects of dopant addition on transport characteristics of transparent conducting oxides (TCOs) and are critical to further improvement and optimization of TCO properties.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, year={2006}, month={Aug}, pages={033713} }
 @article{chugh_ramachandran_tiwari_narayan_2006, title={Epitaxial ZnO/Pt layered structures and ZnO-Pt nanodot composites on sapphire (0001)}, volume={35}, ISSN={["1543-186X"]}, DOI={10.1007/BF02692537}, number={5}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Chugh, Amit and Ramachandran, S. and Tiwari, A. and Narayan, J.}, year={2006}, month={May}, pages={840–845} }
 @article{tiwari_bhosle_ramachandran_sudhakar_narayan_budak_gupta_2006, title={Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2193431}, DOI={10.1063/1.2193431}, abstractNote={We report room temperature ferromagnetism in single crystal Ce1−xCoxO2−δ (x⩽0.05) films deposited on a LaAlO3(001) substrate. Films were grown by a pulsed laser deposition technique and were thoroughly characterized using x-ray diffraction, high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy and scanning transmission electron microscopy-Z contrast, x-ray photoelectron spectroscopy, optical transmission spectroscopy, and magnetic measurements. These films are transparent in the visible regime and exhibit a very high Curie temperature ∼740–875K with a giant magnetic moment. Our results indicate that the ferromagnetic property is intrinsic to the CeO2 system and is not a result of any secondary magnetic phase or cluster formation.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Tiwari, Ashutosh and Bhosle, V. M. and Ramachandran, S. and Sudhakar, N. and Narayan, J. and Budak, S. and Gupta, A.}, year={2006}, month={Apr}, pages={142511} }
 @article{tiwari_narayan_2006, title={Growth and observation of low-field giant magnetoresistance in La0.7Sr0.3MnO3/ZnO superlattice structures}, volume={6}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2006.118}, abstractNote={We report the growth of a new class of superlattice structure, consisting of alternate layers of La0.7Sr0.3MnO3 (LSMO) and ZnO, which exhibits giant magnetoresistance at low fields. These superlattices were fabricated using a novel pulsed-laser deposition
 technique with a specially designed target assembly. Giant magnetoresistance of >250% has been observed in these structures in current-in-plane configuration on the application of just ∼400 Gauss of magnetic field over the broad temperature range 15–200 K. Observation of giant
 magnetoresistance at such low magnetic fields is a groundbreaking step in the field of novel magnetic materials and devices.}, number={3}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Tiwari, A and Narayan, J}, year={2006}, month={Mar}, pages={612–617} }
 @article{ramachandran_chugh_tiwari_narayan_2006, title={Growth of highly conducting epitaxial ZnO-Pt-ZnO heterostructure on alpha-Al2O3 (0001)}, volume={291}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2006.02.010}, abstractNote={Here we report the growth of epitaxial ZnO–Pt–ZnO trilayer structures on sapphire (0 0 0 1) substrate by using pulsed laser deposition technique. These structures were characterized using X-ray diffraction, conventional and high-resolution transmission electron microscopy, STEM (scanning Transmission Electron microscopy-Atomic number) Z-contrast, optical transmittance and electrical resistivity measurements. X-ray diffraction and TEM experiments revealed the epitaxial nature of these structures, the orientation relationship being: 〈1 1 1〉pt||〈0 0 0 1〉ZnO||〈0 0 0 1〉〈0 0 0 1〉sapphire (out of plane) and 〈1 1 0〉pt||〈2 1¯ 1¯ 0〉ZnO||〈0 1 1¯ 0〉sapphire (in Plane) for the trilayer structure. Electrical and optical measurements showed that these heterostructures exhibit quite good electrical conductivity and at the same time possess moderate optical transmittance.}, number={1}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Ramachandran, S. and Chugh, A. and Tiwari, A. and Narayan, J.}, year={2006}, month={May}, pages={212–217} }
 @article{trichy_narayan_zhou_2006, title={L10 ordered epitaxial FePt (001) thin films on TiN∕Si (100) by pulsed laser deposition}, volume={89}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2357848}, DOI={10.1063/1.2357848}, abstractNote={Epitaxially oriented magnetic FePt (001) thin films were grown on Si (001) substrates with TiN as a template buffer by using pulsed laser deposition. The epitaxial relationship and presence of L10 ordering were studied by x-ray diffraction and further confirmed by detailed transmission electron microscopy. The effectiveness of using TiN (diamagnetic metal) as a template, for an epitaxial magnetic FePt heterostructure integrated with silicon and for inducing L10 order in the FePt films, has been demonstrated. Magnetic measurements show that the ordered FePt films are predominantly perpendicularly magnetized and have high values of coercivity suitable for magnetic recording applications.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Trichy, G. R. and Narayan, J. and Zhou, H.}, year={2006}, month={Sep}, pages={132502} }
 @article{bhosle_tiwari_narayan_2006, title={Metallic conductivity and metal-semiconductor transition in Ga-doped ZnO}, volume={88}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2165281}, DOI={10.1063/1.2165281}, abstractNote={This letter reports the metallic conductivity in Ga:ZnO system at room temperature and a metal-semiconductor transition (MST) behavior at low temperatures. Zn0.95Ga0.05O films, deposited by pulsed laser deposition in the pressure range of ∼10−2Torr of oxygen, were found to be crystalline and exhibited degeneracy at room temperature with the electrical resistivity close to 1.4×10−4Ωcm and transmittance >80% in the visible region. Temperature dependent resistivity measurements of these highly conducting and transparent films also showed, for the first time, a MST at ∼170K. Mechanisms responsible for these observations are discussed in the terms of dopant addition and its effect on ionization efficiency of oxygen vacancies.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, year={2006}, month={Jan}, pages={032106} }
 @article{narayan_bhosle_tiwari_gupta_kumar_wu_2006, title={Methods for processing tantalum films of controlled microstructures and properties}, volume={24}, ISSN={["0734-2101"]}, DOI={10.1116/1.2335863}, abstractNote={The authors have fabricated thin films of alpha tantalum (α-Ta) with crystalline and amorphous structures by nonequilibrium pulsed laser deposition techniques, and compared their electrical properties and diffusion characteristics with those of polycrystalline beta tantalum (β-Ta) films produced by magnetron sputtering. The microstructure and atomic structure of these films were studied by x-ray diffraction and high-resolution electron microscopy, while elemental analysis was performed using electron energy-loss spectroscopy and x-ray dispersive analysis. The α-Ta with body-centered-cubic structure was formed only under clean, impurity-free conditions of laser molecular beam epitaxy. The resistivity measurements in the temperature range of 10–300K showed room-temperature values to be 15–30μΩcm for α-Ta, 180–200μΩcm for β-Ta, and 250–275μΩcm for amorphous tentalum (a-Ta). The temperature coefficients of resistivity (TCRs) for α-Ta and β-Ta were found to be positive with characteristic metallic behavior, while TCR for a-Ta was negative, characteristic of high-resistivity disordered metals. The authors discuss the mechanism of formation of a-Ta and show that it is stable in the temperature range of 650–700°C. Electron energy-loss spectroscopy (EELS) and Rutherford backscattering measurements showed oxygen content in a-Ta films to be less than 0.1%. The secondary ion mass spectrometry, scanning transmission electron microscope Z-contrast imaging, and EELS studies show that, after 650°C annealing for 1h, a-Ta films have less than 10nm Cu diffusion distance while polycrystalline Ta films have substantial Cu diffusion. The superior diffusion barrier properties of a-Ta for Cu metallization have been attributed to the lack of grain boundaries which usually lead to enhanced diffusion in the case of polycrystalline α-Ta and β-Ta films. Thus, superior diffusion properties of a-Ta provide an optimum solution for copper metallization in next-generation silicon microelectronic devices.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Narayan, J. and Bhosle, V. and Tiwari, A. and Gupta, A. and Kumar, P. and Wu, R.}, year={2006}, pages={1948–1954} }
 @misc{narayan_tiwari_2006, title={Methods of forming three-dimensional nanodot arrays in a matrix}, volume={7,105,118}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J. and Tiwari, A.}, year={2006} }
 @article{bhosle_narayan_2006, title={Microstructure and electrical property correlations in Ga:ZnO transparent conducting thin films}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2360777}, DOI={10.1063/1.2360777}, abstractNote={In this paper, we report correlations between processing, microstructure, and electrical properties of Ga doped ZnO films. Films with different grain sizes were grown on amorphous glass substrate by changing the substrate and pulsed laser deposition variables. The results corresponding to these films were compared with those from epitaxial single crystal films grown on (0001) sapphire. Microstructural characteristics were analyzed in detail by using x-ray diffraction and transmission electron microscopy. Electrical properties were evaluated by resistivity measurements in the temperature range of 15–300K and Hall measurements at room temperature. It was observed that the grain boundaries and orientation of grains (texture characteristics) affected the carrier concentration and the mobility considerably in nanocrystalline films deposited on glass substrates. This effect is envisaged to occur as a result of trapping of electrons and buildup of a potential barrier across the grain boundaries. However, the resistivity in nanocrystalline films could be decreased significantly by carefully controlling the deposition conditions. For a film deposited on glass at 200°C and 1mtorr of oxygen partial pressure, we attained a minimum resistivity value of 1.8×10−4Ωcm. The epitaxial films on sapphire substrates showed a resistivity of 1.4×10−4Ωcm, deposited at 400°C and pressure of 2.4×10−2torr. The role of grain boundaries and defects in controlling the carrier generation and transport has been discussed in detail and the possible mechanisms limiting the electrical conductivity in films with different microstructures have also been identified.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhosle, V. and Narayan, J.}, year={2006}, month={Nov}, pages={093519} }
 @article{narayan_bhosle_2006, title={Phase transition and critical issues in structure-property correlations of vanadium oxide}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2384798}, DOI={10.1063/1.2384798}, abstractNote={Vanadium oxide (VO2) exhibits a very interesting semiconductor to metal transition as the crystal structure changes from tetragonal or rutile to monoclinic upon cooling close to 68°C. The characteristics of this transition are very interesting scientifically and are of immense technological importance due to a variety of sensor- and memory-type applications. We have processed high-quality films of VO2 by pulsed laser deposition, which were grown epitaxially on (0001) sapphire substrate via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the sapphire substrate. These films exhibit a sharp transition near 68°C, large amplitude, and very small hysteresis, similar to bulk single crystal of VO2. The sharpness and amplitude of the transition and the hysteresis upon heating and cooling are found to be a strong function of crystal structure and microstructure (grain size, characteristics of grain boundaries, and defect content). Here, we propose a model to establish microstructure-property correlations in crystalline and amorphous phases of VO2, which can be used to rationalize our experimental observations as well as those available in the literature. Based upon this model, we predict specific microstructures leading to properties needed for various sensor- and memory-type devices.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Narayan, J. and Bhosle, V. M.}, year={2006}, month={Nov}, pages={103524} }
 @article{porter_muth_narayan_foreman_everitt_2006, title={Photoluminescence study of ZnO films codoped with nitrogen and tellurium}, volume={100}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2372312}, DOI={10.1063/1.2372312}, abstractNote={Epitaxial ZnO films codoped with tellurium and nitrogen were grown by pulsed laser deposition on c-axis oriented sapphire substrates. The codoping strategy allowed the resistivity of the films to be controlled over several orders of magnitude and may prove useful in the development of ZnO based light emitters. Photoluminescence studies of tellurium-doped, nitrogen-doped, tellurium and nitrogen codoped, and undoped ZnO films were conducted. Strong room temperature photoluminescence and stimulated emission were observed in the undoped and Te-doped films, but not in codoped films. Time-resolved photoluminescence measurements indicated that carrier lifetime was significantly reduced in doped ZnO as compared to undoped ZnO.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Porter, H. L. and Muth, J. F. and Narayan, J. and Foreman, John V. and Everitt, Henry O.}, year={2006}, month={Dec}, pages={123102} }
 @article{ramachandran_jung_narayan_conrad_2006, title={Regular and high resolution transmission electron microscopy observations on the precipitates in a naturally aged Al–Mg–Si alloy AA6022}, volume={435-436}, ISSN={0921-5093}, url={http://dx.doi.org/10.1016/j.msea.2006.07.139}, DOI={10.1016/j.msea.2006.07.139}, abstractNote={The precipitates in the Al–Mg–Si alloy AA6022 naturally aged for 2–3 years were investigated by regular and high resolution transmission electron microscopy (TEM and HRTEM) and by selective area electron diffraction (SAED). The shape of the particles was generally either nearly circular or circular with one or more bulges. They had an approximate log-normal size distribution with a peak diameter dp = 2.75 nm. Their crystal structure matched that of the c-centered monoclinic β// phase (GP-II Zone) reported in the literature for aging of this alloy type at elevated temperatures.}, journal={Materials Science and Engineering: A}, publisher={Elsevier BV}, author={Ramachandran, S. and Jung, K. and Narayan, J. and Conrad, H.}, year={2006}, month={Nov}, pages={693–697} }
 @article{zhou_narayan_2006, title={Self-assembled magnetic nanostructures: Epitaxial Ni nanodots on TiN/Si (001) surface}, volume={8}, ISSN={1388-0764 1572-896X}, url={http://dx.doi.org/10.1007/s11051-006-9098-1}, DOI={10.1007/s11051-006-9098-1}, number={5}, journal={Journal of Nanoparticle Research}, publisher={Springer Science and Business Media LLC}, author={Zhou, H. and Narayan, J.}, year={2006}, month={Aug}, pages={595–600} }
 @article{conrad_ramachandran_jung_narayan_2006, title={Transmission electron microscopy observations on the microstructure of naturally aged Al-Mg-Si alloy AA6022 processed with an electric field}, volume={41}, ISSN={["1573-4803"]}, DOI={10.1007/s10853-006-0840-y}, number={22}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Conrad, H. and Ramachandran, S. and Jung, K. and Narayan, J.}, year={2006}, month={Nov}, pages={7555–7561} }
 @article{damjanovic_bolla_singh_poole_senter_narayan_2005, title={Effect of UV/VUV enhanced RTP on process variation and device performance of metal gate high-kappa gate stacks for the sub-90-nm CMOS regime}, volume={18}, DOI={10.1109/TSM.2004.841823}, abstractNote={We show that UV/VUV-enhanced rapid thermal processing (RTP) in combination with single-wafer processing using a single tool for the fabrication of metal gate/high-/spl kappa/ dielectric gate stacks not only improves overall device performance, but also leads to a significant reduction in process variation at the front end of the CMOS process flow for the sub-90-nm technology node. The gate stacks were fabricated under various UV/VUV conditions. Gate stacks processed under UV/VUV radiation during all processing steps displayed low leakage currents of the order of 10/sup -11/ A/cm/sup 2/. It is shown that the Al-Al/sub 2/O/sub 3/-Si gate stacks processed under UV/VUV conditions also display the lowest variations both in mean leakage current and mean capacitance, as compared to devices where UV/VUV was not used for all the processing steps. Therefore, it can be see that reliance on successive corrective iterations common to automatic process control or standard design simulation can be reduced significantly. As a result, UV/VUV-enhanced RTP has the potential to reduce the effect of process variations on overall device performance, thereby making the overall process more cost effective and time efficient and therefore improving yield and device reliability.}, number={1}, journal={IEEE Transactions on Semiconductor Manufacturing}, author={Damjanovic, D. and Bolla, H. K. and Singh, R. and Poole, K. F. and Senter, H. F. and Narayan, Jagdish}, year={2005}, pages={55–62} }
 @article{tiwari_jin_narayan_park_2005, title={Electrical transport in ZnO(1-delta)films: Transition from band-gap insulator to Anderson localized insulator (vol 96, pg 3827, 2004)}, volume={97}, number={5}, journal={Journal of Applied Physics}, author={Tiwari, A. and Jin, C. and Narayan, J. and Park, M.}, year={2005} }
 @article{porter_cai_muth_narayan_2005, title={Enhanced photoconductivity of ZnO films Co-doped with nitrogen and tellurium}, volume={86}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1923194}, DOI={10.1063/1.1923194}, abstractNote={Zinc oxide films are typically found to be n type, and conductive under most growth conditions and growth methods. Co-doping with multiple elements is one strategy for improving the electrical and optical properties of zinc oxide materials for optoelectronic device applications. Using pulsed-laser deposition, thin ZnO films were grown on c-axis oriented sapphire. The films were co-doped with nitrogen and tellurium. Depending on the relative concentrations of the dopants, the resistivity of the films was observed to increase by several orders of magnitude, significantly improving the photoconductive response. The enhancement of the photosensitivity reached a maximum at a tellurium concentration of around 1020cm−3.}, number={21}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Porter, H. L. and Cai, A. L. and Muth, J. F. and Narayan, J.}, year={2005}, month={May}, pages={211918} }
 @article{bhosle_tiwari_narayan_2005, title={Epitaxial growth and properties of MoOx(2<x<2.75) films}, volume={97}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1868852}, DOI={10.1063/1.1868852}, abstractNote={We report the growth of epitaxial molybdenum oxide (MoOx,2<x<2.75) films on c plane of sapphire substrate using pulsed laser deposition in oxygen environment. The structure was characterized using x-ray diffraction, high resolution transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). Electrical resistivity and optical properties were investigated using four-point-probe resistivity measurements and spectroscopy techniques, respectively. It was found that the film had a monoclinic structure based on MoO2 phase and showed an unusual combination of high conductivity and high transmittance in the visible region after annealing. The unusual combination of these properties was realized by systematically controlling the relative fraction of different oxidation states of molybdenum, namely Mo4+, Mo5+, and Mo6+ in the monoclinic phase. For a film 60nm thick and annealed at 250°C for 1h, the ratio of Mo6+∕(Mo4++Mo5+) was determined to be ∼2.9∕1 using XPS, and a typical value of transmittance was ∼65% and resistivity close to 1×10−3Ωcm. These results demonstrate growth of epitaxial MoOx films with tunable electrical and optical properties. Further optimization of these properties is expected to result in applications related to display panels, solar cells, chromogenic (photochromic, electrochromic, gasochromic) devices, and transparent conducting oxides. Our ability to grow epitaxial MoOx films can further aid their integration with optoelectronic and photonic devices.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, year={2005}, month={Apr}, pages={083539} }
 @article{ramachandran_tiwari_narayan_prater_2005, title={Epitaxial growth and properties of Zn1−xVxO diluted magnetic semiconductor thin films}, volume={87}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2112185}, DOI={10.1063/1.2112185}, abstractNote={Here we report systematic studies on the epitaxial growth and properties of Zn1−xVxO[x=0.001-0.2] thin films deposited onto sapphire c-plane single crystals. The thin films were deposited using pulsed laser deposition technique and were found to be epitaxial in nature. X-ray diffraction and high resolution transmission electron microscopy were employed to study the epitaxial relations of Zn1−xVxO with the sapphire substrate and electron energy loss spectroscopy was used to establish the bonding characteristics and oxidation states of vanadium inside the ZnO host. The main emphasis is on the magnetic properties of this system taking into consideration the phase purity and microstructural characteristics of these films. Our results show that the Zn1−xVxO system, with V in zinc substitutional sites, does not exhibit any signature of ferromagnetism, both at room temperature as well as at lower temperatures down to 10 K.}, number={17}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Ramachandran, S. and Tiwari, A. and Narayan, J. and Prater, J. T.}, year={2005}, month={Oct}, pages={172502} }
 @article{jin_narayan_tiwari_zhou_kvit_narayan_2005, title={Epitaxial growth of zinc oxide thin films on silicon}, volume={117}, ISSN={0921-5107}, url={http://dx.doi.org/10.1016/j.mseb.2004.12.003}, DOI={10.1016/j.mseb.2004.12.003}, abstractNote={Epitaxial zinc oxide thin films were grown on Si(1 1 1) using aluminum nitride and magnesium oxide/titanium nitride buffer layers. The resultant films were examined using transmission electron microscopy, X-ray diffraction, electrical conductivity, and photoluminescence spectroscopy. The following epitaxial relationships were observed in the ZnO/AlN/Si(1 1 1) heterostructure: ZnO[0 0 0 1] || AlN[0 0 0 1] || Si[1 1 1] along the growth direction, and ZnO[21¯1¯0] || AlN[21¯1¯0] || Si[011¯] along the in-plane direction. Domain-matching epitaxial growth of TiN on Si(1 1 1) substrate allows successful epitaxial growth of MgO and ZnO layers in a ZnO/MgO/TiN/Si(1 1 1) heterostructure. The epitaxial relationships observed for this heterostructure were ZnO[0 0 0 1] || MgO/TiN/Si[1 1 1] along the growth direction and ZnO[21¯1¯0] || MgO/TiN/Si[011¯] along in-plane direction. The resultant ZnO films demonstrate excellent electrical and optical properties. ZnO thin films exhibit extremely bright ultraviolet luminescence with relatively weak green-band emission.}, number={3}, journal={Materials Science and Engineering: B}, publisher={Elsevier BV}, author={Jin, Chunming and Narayan, Roger and Tiwari, Ashutosh and Zhou, Honghui and Kvit, Alex and Narayan, Jagdish}, year={2005}, month={Mar}, pages={348–354} }
 @article{conrad_narayan_jung_2005, title={Grain size softening in nanocrystalline TiN}, volume={23}, ISSN={["0263-4368"]}, DOI={10.1016/j.ijrmhm.2005.04.016}, abstractNote={The effect of grain size d on the hardness H of TiN is considered, with focus on the nanometer grain size range. H increases from ∼22 GPa to ∼32 GPa with decrease in d from single crystals to d = 50 nm. Three sets of data show that H decreases with further reduction in d below 50 nm, i.e., grain size softening occurs. The softening is not in complete or unequivocal accord with any of the three models normally proposed for such softening, namely Coble creep, grain boundary shear and dislocation line tension modification. Factors which could have contributed to the softening are: (a) changes in texture and in turn the corresponding value of the Taylor orientation factor M and (b) the presence of weakening imperfections produced during fabrication.}, number={4-6}, journal={INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS}, author={Conrad, H and Narayan, J and Jung, K}, year={2005}, pages={301–305} }
 @article{narayan_2005, title={New frontiers in thin film growth and nanomaterials}, volume={36A}, ISSN={["1543-1940"]}, DOI={10.1007/s11661-005-0301-2}, number={2}, journal={METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE}, author={Narayan, J}, year={2005}, month={Feb}, pages={277–294} }
 @article{narayan_2005, title={New frontiers in thin film growth and nanomaterials}, volume={36}, ISSN={1073-5615 1543-1916}, url={http://dx.doi.org/10.1007/s11663-005-0001-8}, DOI={10.1007/s11663-005-0001-8}, number={1}, journal={Metallurgical and Materials Transactions B}, publisher={Springer Science and Business Media LLC}, author={Narayan, Jagdish}, year={2005}, month={Feb}, pages={5–22} }
 @article{tiwari_jin_narayan_park_2005, title={Publisher's Note: “Electrical transport in ZnO1−δfilms: Transition from band-gap insulator to Anderson localized insulator” [J. Appl. Phys. 96, 3827 (2004)]}, volume={97}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1861992}, DOI={10.1063/1.1861992}, abstractNote={FIG. 2. Raman spectra for various ZnO 1-␦ films. Inset shows the variation in the position of E 2͑2͒ peak with oxygen pressure during the thin film growth.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Tiwari, Ashutosh and Jin, C. and Narayan, J. and Park, M.}, year={2005}, month={Mar}, pages={059902} }
 @article{tiwari_jin_narayan_park_2004, title={Electrical transport in ZnO1-delta films: Transition from band-gap insulator to Anderson localized insulator}, volume={96}, ISSN={["0021-8979"]}, DOI={10.1063/1.1783591}, abstractNote={We have thoroughly investigated the effect of oxygen nonstoichiometry on the electrical transport characteristics of ZnO1−δ films. These films were grown on optical grade quartz substrates by using a pulsed laser deposition technique. In order to alter the amount of oxygen nonstoichiometry (δ), oxygen partial pressure during the film growth was systematically varied from 102Torrto10−5Torr. Qualitative estimates about the amount of oxygen nonstoichiometry in these films were made using Raman Spectroscopy data. High resolution electrical resistivity and thermoelectric power measurements were performed in the temperature range 12–300K. A detailed analysis of electrical transport data showed a transition from band-gap insulating state (for the films prepared at high oxygen environments) to Anderson localized insulating state (for the films prepared at lower oxygen environments).}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tiwari, A and Jin, C and Narayan, J and Park, M}, year={2004}, month={Oct}, pages={3827–3830} }
 @article{rawdanowicz_narayan_2004, title={Epitaxial GaN on Si(111): Process control of SiNx interlayer formation}, volume={85}, ISSN={["1077-3118"]}, DOI={10.1063/1.1771803}, abstractNote={The heteroepitaxial growth of (0001) GaN thin films directly on (111) Si by laser-molecular beam epitaxy without the formation of a SiNx interlayer at the GaN∕Si interface is reported. We also find that SiNx can be formed subsequently as a result of nitrogen diffusion to the GaN∕Si(111) interface. The orientation relationship of GaN on Si(111) was determined using x-ray diffraction and selected area electron diffraction. The atomic structure of the interfaces was studied by high resolution transmission electron microscopy. A Fourier filtered image of the cross-sectional GaN∕Si(111) interface demonstrated domain matching epitaxy of 6:5. Distributions of N and Ga concentrations near the GaN∕Si interface were determined using electron energy loss spectroscopy.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Rawdanowicz, TA and Narayan, J}, year={2004}, month={Jul}, pages={133–135} }
 @article{tiwari_narayan_sudhakar_rajeev_2004, title={Growth of single-phase c-axis aligned La1.2Ca1.8Mn2O7 films on SrTiO3(001)}, volume={132}, ISSN={["0038-1098"]}, DOI={10.1016/j.ssc.2004.08.015}, abstractNote={We report the growth of single phase, c-axis aligned thin films of La1.2Ca1.8Mn2O7 on SrTiO3 (001) substrates using a controlled pulsed laser deposition method. In this method, constraint of epitaxy is utilized to stabilize the Ruddlesdon–Popper (RP) phase of La1.2Ca1.8Mn2O7. Oxygen ambient pressure and the rate of deposition play a very important role in influencing the epitaxial growth as well as maintaining phase purity of the material. The oxygen pressure inside the deposition chamber was very precisely controlled and varied during the layer-by-layer growth of the film. Films, prepared by our method, show excellent electrical and magnetic characteristics with a sharp metal–insulator transition at TM–I=90 K, closely followed by a magnetic transition at TC=91 K.}, number={12}, journal={SOLID STATE COMMUNICATIONS}, author={Tiwari, A and Narayan, J and Sudhakar, N and Rajeev, KP}, year={2004}, month={Dec}, pages={863–866} }
 @article{narayan_tiwari_2004, title={Novel methods of forming self-assembled nanostructured materials: Ni nanodots in Al2O3 and TiN matrices}, volume={4}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2004.107}, abstractNote={We have developed two novel methods of growing self-assembled nanodot arrays of uniform size (diameter 2-50 nm) of a variety of materials in crystalline as well as amorphous matrices. These methods employ a pulsed laser deposition technique and are classified as: (a) sequential growth method; and (b) simultaneous growth method. In the first method, the nanodots and matrix material are formed sequentially, while in the second method, nanodots and matrix materials grow simultaneously. In the sequential growth, self-assembly of nanodots is controlled by the flux of materials, interfacial energy, intervening matrix layer, substrate and laser parameters. For the simultaneous growth method of self-assembly of nanodots, there is additional requirement that the material of the nanodot and the matrix should be such that the Gibb's free energy of oxidation of the constituent of matrix material is much lower than that of the nanodot material.}, number={7}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Narayan, J and Tiwari, A}, year={2004}, month={Sep}, pages={726–732} }
 @article{ramachandran_tiwari_narayan_2004, title={Origin of room-temperature ferromagnetism in cobalt-doped ZnO}, volume={33}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-004-0156-0}, number={11}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Ramachandran, S and Tiwari, A and Narayan, J}, year={2004}, month={Nov}, pages={1298–1302} }
 @article{wang_gupta_tiwari_zhang_narayan_2004, title={TaN-TiN binary alloys and superlattices as diffusion barriers for copper interconnections}, volume={33}, ISSN={0361-5235 1543-186X}, url={http://dx.doi.org/10.1007/S11664-004-0300-X}, DOI={10.1007/s11664-004-0300-x}, number={1}, journal={Journal of Electronic Materials}, publisher={Springer Science and Business Media LLC}, author={Wang, H. and Gupta, A. and Tiwari, Ashutosh and Zhang, X. and Narayan, J.}, year={2004}, month={Jan}, pages={L5–L5} }
 @article{fakhruddin_singh_poole_kondapi_narayan_2004, title={The effect of interfacial layers on high-performance gate dielectrics processed by RTP-ALD}, volume={151}, ISSN={["1945-7111"]}, DOI={10.1149/1.1768132}, abstractNote={In this paper we present the role of the ultrathin interfacial silicon-oxide layer on the performance of high-k dielectrics. We deposited ZrO 2 by rapid thermal process atomic layer deposition (RTP-ALD) and studied the electrical conduction mechanism of the films. As the quality of the interfacial layer may seriously influence the performance of a high-dielectric-constant gate material, we designed a number of experiments to understand the role of the interfacial layer. Some of these experiments include the study of an identical thermal cycle with and without use of the precursor for the deposition of ZrO 2 films. In the transmission electron microscopy (TEM) micrographs (especially in STEM-Z) the formation of amorphous silica and crystalline zirconia exhibit a distinct periodicity characteristic of spinodal decomposition. This feature, along with atomic-level sharpness of the interface, may hold the key to excellent electrical properties reported in this paper. The ultrathin interfacial silicon oxide layer has the ability to accommodate the strain between silicon and the mixed phase material without creating significant defects at the interface.}, number={8}, journal={JOURNAL OF THE ELECTROCHEMICAL SOCIETY}, author={Fakhruddin, M and Singh, R and Poole, KF and Kondapi, SV and Narayan, J}, year={2004}, pages={G507–G511} }
 @misc{narayan_2004, title={The global economy}, volume={56}, number={11}, journal={JOM: the Journal of the Minerals, Metals & Materials Society}, author={Narayan, J. A.}, year={2004}, pages={11-} }
 @article{ramachandran_tiwari_narayan_2004, title={Zn0.9Co0.1O-based diluted magnetic semiconducting thin films}, volume={84}, ISSN={["1077-3118"]}, DOI={10.1063/1.1764936}, abstractNote={Here we report a systematic study of structural, optical, and magnetic measurements on epitaxial Zn0.9Co0.1O films grown on c-plane sapphire single crystal, at various temperatures (500–650°C), using pulsed-laser deposition. The main emphasis in this work has been on the correlation of microstructure with properties, specifically with magnetic properties and the fate of cobalt ions into substitutional sites versus precipitates. The reasons for room-temperature ferromagnetism are explored, and convincingly proved to be one of the inherent properties of the material. Most importantly, the presence of nanoclusters of any magnetic phase was ruled out. This was determined by high-resolution transmission electron microscopy, coupled with electron energy loss spectroscopy and STEM-Z (scanning transmission electron microscopy-atomic number) contrast studies.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Ramachandran, S and Tiwari, A and Narayan, J}, year={2004}, month={Jun}, pages={5255–5257} }
 @article{chugh_tiwari_kvit_narayan_2003, title={A novel technique for making self-encapsulated and self-aligned copper films}, volume={103}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(03)00148-x}, abstractNote={We provide a method to grow self-aligned epitaxial MgO/Cu/MgO films on silicon substrates by pulsed laser deposition (PLD) technique. Here, a thin layer of Cu/Mg (Mg 5%) is deposited using a PLD over Si (100) specimens, followed by annealing at 500 °C in a controlled oxygen environment resulting in the segregation of Mg on either side of the copper film. Mg on the upper side of copper reacts with ambient oxygen and on the lower side with the adsorbed oxygen in the substrate to form layers of MgO. High-resolution transmission electron microscopy (HRTEM) measurements showed thin layers of MgO formed on either side of the copper films. The lower MgO layer acts as a diffusion barrier and inhibits the diffusion of Cu into the system while the upper MgO layer acts as a passivating layer and protects copper against oxidation. This approach can also be used to grow high quality epitaxial YBa2Cu3O7−δ films with MgO acting as a buffer for the superconducting device applications.}, number={1}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Chugh, A and Tiwari, A and Kvit, A and Narayan, J}, year={2003}, month={Sep}, pages={45–48} }
 @article{gupta_wang_kvit_duscher_narayan_2003, title={Effect of microstructure on diffusion of copper in TiN films}, volume={93}, ISSN={["1089-7550"]}, DOI={10.1063/1.1566472}, abstractNote={We investigated the effect of the microstructure of TiN films on the diffusion behavior of Cu. Cu/TiN films were synthesized on Si(100) substrate by the pulsed laser deposition (PLD) technique. Three different microstructures of TiN were achieved by growing the films at different substrate temperatures, where higher deposition temperatures (∼650 °C) led to epitaxial growth by the mechanism of domain matching epitaxy and lower temperature depositions resulted in polycrystalline and nanocrystalline TiN films. These structures were characterized using x-ray diffraction and high-resolution transmission electron microscopy. Cu was deposited in situ on the samples with three different microstructures of TiN films on Si(100) by PLD. All three samples were simultaneously annealed at 500 °C for 30 min in high vacuum to study the effect of diffusion characteristics of Cu as a function of microstructure of the TiN films. Secondary ion mass spectroscopy, Z-contrast imaging and electron energy-loss spectroscopy were used to understand the diffusion mechanisms and rationalize results in different microstructures.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Gupta, A and Wang, H and Kvit, A and Duscher, G and Narayan, J}, year={2003}, month={May}, pages={5210–5214} }
 @article{zhou_kumar_kvit_tiwari_narayan_2003, title={Formation of self-assembled epitaxial nickel nanostructures}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1609046}, abstractNote={Highly orientated nickel magnetic nanoparticles were obtained by pulsed laser deposition technique on silicon (100) substrate using epitaxial titanium nitride film as the template. These nanoparticles have been characterized by conventional and high-resolution transmission electron microscopy, scanning transmission electron microscopy Z-contrast imaging, and x-ray diffraction techniques. The results have shown that the growth of nickel on epitaxially grown titanium nitride follows a three-dimensional island growth mechanism. The predominant orientation of nickel islands observed is Ni(100)∥TiN(100)∥Si(100), the so-called “cube-on-cube” orientation relation. The islands are faceted with a truncated pyramidal shape and bounded by (111) planes at sides and (100) plane at the top. Islands with nontruncated pyramidal shape were also found in some samples, but with rotational orientation relations, where the nickel crystal rotates with an approximate angle of 90° with respect to one of TiN 〈110〉 directions parallel to the interface. The appearance of this rotational epitaxial growth did not show any obvious deposition temperature dependence in the range of 400–650 °C, rather it seemed to be closely related to the crystalline quality of TiN template. The actual size of islands varies from a few nanometers to tens of nanometers, depending on the deposition time and temperature. The three-dimensional growth of nickel islands and the island faceting could be explained by the surface energy anisotropy of both nickel and titanium nitride.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Zhou, H and Kumar, D and Kvit, A and Tiwari, A and Narayan, J}, year={2003}, month={Oct}, pages={4841–4846} }
 @article{wang_zhang_gupta_tiwari_narayan_2003, title={Growth and characteristics of TaN/TiN superlattice structures}, volume={83}, ISSN={["0003-6951"]}, DOI={10.1063/1.1616656}, abstractNote={Epitaxial B1 NaCl-structured TaN(3 nm)/TiN(2 nm) superlattice structures were grown on Si(100) substrates with a TiN buffer layer, using pulsed-laser deposition. A special target assembly was used to manipulate the thickness of each layer. X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy (Z contrast) studies confirmed the single-crystalline nature of the superlattice with a uniform layer structure. Nanoindentation results suggest the high hardness of these superlattice structures. Four-point-probe resistivity measurements show low resistivity of the heterostructures and a Cu diffusion characteristic study proved this superlattice system can be a promising diffusion barrier and can withstand 700 °C annealing for 30 min.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Wang, H and Zhang, X and Gupta, A and Tiwari, A and Narayan, J}, year={2003}, month={Oct}, pages={3072–3074} }
 @article{gilmore_chattopadhyay_kvit_sharma_lee_collis_sankar_narayan_2003, title={Growth, characterization,, and electrical properties of PbZr0.52Ti0.48O3 thin films on buffered silicon substrates using pulsed laser deposition}, volume={18}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.2003.0016}, abstractNote={Epitaxial thin films of PbZr0.52Ti0.48O3 (PZT) were synthesized successfully on SrRuO3/SrTiO3/MgO/TiN/Si heterostructures by pulsed laser deposition. The films were single phase and had (001) orientation. The deposition parameters were varied to obtain the best epitaxial layer for each of the compounds. Transmission electron microscopy indicated good epitaxy for the entire heterostructure and sharp interfaces between the epilayers. Dielectric and P–E hysteresis loop measurements were carried out with evaporated Ag electrodes. The dielectric constant for the films was found to be between 400–450. The value of saturation polarization Ps was between 55–60 μC/cm2, and the coercive field Ec varied from 60–70 kV/cm. Integration of PZT films with silicon will be useful for future memory and micromechanical devices.}, number={1}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Gilmore, WM and Chattopadhyay, S and Kvit, A and Sharma, AK and Lee, CB and Collis, WJ and Sankar, J and Narayan, J}, year={2003}, month={Jan}, pages={111–114} }
 @misc{narayan_sharma_muth_2003, title={Method for making optoelectronic and microelectronic devices including cubic ZnMgO and/or CdMgO alloys}, volume={6,518,077}, number={2003 Feb. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J. and Sharma, A. K. and Muth, J. F.}, year={2003} }
 @article{haverkamp_mayo_bourham_narayan_jin_duscher_2003, title={Plasma plume characteristics and properties of pulsed laser deposited diamond-like carbon films}, volume={93}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1555695}, DOI={10.1063/1.1555695}, abstractNote={Pulsed laser deposition is a unique technique for the deposition of hydrogen-free diamond-like carbon films. During deposition, amorphous carbon is evaporated from a solid target by a high-energy KrF laser, ionized, and ejected as a plasma plume. The plume expands outwards and deposits the target material on a substrate. The plasma properties of the plume determine the quality of the thin films deposited on the substrate. These plume properties include ion density, ion flow speed, electron temperature, and plume peaking parameter. In this research, a triple Langmuir probe is used to determine various plasma properties of the plume created from the pulsed laser ablation of amorphous graphite as a function of laser energy density and laser spot size on the target. A thin diamond-like carbon film is deposited and analyzed with electron energy-loss spectroscopy to determine the sp3/sp2 fraction. A special preparation technique was used to prepare the thin film for analysis to prevent the damage that may be caused by conventional ion milling techniques.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Haverkamp, J. and Mayo, R. M. and Bourham, M. A. and Narayan, J. and Jin, C. and Duscher, G.}, year={2003}, month={Mar}, pages={3627–3634} }
 @article{kumar_yarmolenko_sarkar_narayan_zhou_tiwari_2004, title={Pulsed laser deposition assisted novel synthesis of self-assembled magnetic nanoparticles}, volume={35}, ISSN={["1359-8368"]}, DOI={10.1016/j.compositesb.2003.08.002}, abstractNote={We report here a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline materials with accurate size and interface control with improved magnetic properties. Using this method, single-domain nanocrystalline Fe and Ni particles in the 5–10 nm size range embedded in amorphous alumina as well as in crystalline TiN have been produced. By controlling the size distribution in confined layers, it was possible to tune the magnetic properties from superparamagnetic to ferromagnetic behavior. Magnetic hysteresis characteristics below the blocking temperature are consistent with single-domain behavior. The paper also presents our results from investigations in which scanning transmission electron microscopy with atomic number contrast (STEM-Z) and electron energy loss spectroscopy (EELS) were used to understand the atomic structure of Ni nanoparticles and interface between the nanoparticles and the surrounding matrices. It was interesting to learn from EELS measurements at interfaces of individual grains that Ni in alumina matrix does not form an ionic bond indicating the absence of metal–oxygen bond at the interface. The absence of metal–oxygen bond, in turn, suggests the absence of any dead layer on Ni nanoparticles even in an oxide matrix.}, number={2}, journal={COMPOSITES PART B-ENGINEERING}, author={Kumar, D and Yarmolenko, S and Sarkar, J and Narayan, J and Zhou, H and Tiwari, A}, year={2004}, pages={149–155} }
 @article{tiwari_jin_kumar_narayan_2003, title={Rectifying electrical characteristics of La0.7Sr0.3MnO3/ZnO heterostructure}, volume={83}, ISSN={["0003-6951"]}, DOI={10.1063/1.1605801}, abstractNote={We have fabricated a p–n junction, consisting of p-type manganite (La0.7Sr0.3MnO3) and n-type ZnO layers grown on sapphire substrate. This junction exhibits excellent rectifying behavior over the temperature range 20–300 K. Electrical characteristics of La0.7Sr0.3MnO3 (LSMO) film in this heterostructure are found to be strongly modified by the built-in electric field at the junction. It has been shown that by applying the external bias voltage, the thickness of the depletion layer, and hence, the electrical and magnetic characteristics of LSMO film can precisely be modified.}, number={9}, journal={APPLIED PHYSICS LETTERS}, author={Tiwari, A and Jin, C and Kumar, D and Narayan, J}, year={2003}, month={Sep}, pages={1773–1775} }
 @article{tiwari_chugh_jin_narayan_2003, title={Role of self-assembled gold nanodots in improving the electrical and optical characteristics of zinc oxide films}, volume={3}, ISSN={["1533-4880"]}, DOI={10.1166/jnn.2003.217}, abstractNote={We have studied the effect of embedding nanocrystalline Au particles on the electrical and optical characteristics of ZnO films. Au-embedded epitaxial ZnO films were deposited on (0001) sapphire substrates with a pulsed laser deposition technique. The crystalline quality of both the ZnO matrix and Au nanoparticles was investigated by X-ray diffraction and transmission electron microscopy. Composite films were characterized by photoluminescence, optical absorption, and low-temperature electrical resistivity measurements. Photoluminescence spectra of theses films showed a sharp excitonic peak at 3.22 +/- 0.05 eV without any signature of green band emission. Electrical resistivity measurements showed these films to be highly conducting, with a room-temperature resistivity of 3.4 +/- 0.2 m omega-cm.}, number={5}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Tiwari, A and Chugh, A and Jin, C and Narayan, J}, year={2003}, month={Oct}, pages={368–371} }
 @article{kumar_pennycook_narayan_wang_tiwari_2003, title={Role of silver addition in the synthesis of high critical current density MgB2 bulk superconductors}, volume={16}, ISSN={["0953-2048"]}, DOI={10.1088/0953-2048/16/4/306}, abstractNote={Ag-doped MgB2 bulk superconductors have been prepared using a standard solid state processing. The addition of Ag to MgB2 powders during the sintering process has been found to result in an important advantage, namely, the prevention/reduction of loss of Mg, a problem most commonly observed in the sintering of MgB2 bulk samples at elevated temperature and ambient pressures. The Ag-doped MgB2 sample has a distinct superconducting transition temperature around 39 K, while the undoped MgB2 undergoes only a very feeble transition to a diamagnetic superconducting state at around 39 K. The normal conducting silver regions in the MgB2 matrix act as pinning centres resulting in the realization of high critical currents in the presence of magnetic fields.}, number={4}, journal={SUPERCONDUCTOR SCIENCE & TECHNOLOGY}, author={Kumar, D and Pennycook, SJ and Narayan, J and Wang, H and Tiwari, A}, year={2003}, month={Apr}, pages={455–458} }
 @article{zhu_zhang_wang_sergueeva_mukherjee_scattergood_narayan_koch_2003, title={Synthesis of bulk nanostructured Zn by combinations of cryomilling and powder consolidation by room temperature milling: optimizing mechanical properties}, volume={49}, ISSN={["1359-6462"]}, DOI={10.1016/S1359-6462(03)00297-5}, abstractNote={A new technique is used to synthesize nanocrystalline Zn, i.e. cryomilling followed by in situ consolidation of the powders by room temperature ball milling. The room temperature milling appears to sharpen the broad grain size distribution obtained by cryomilling only. Strength and ductility may be optimized in this way by the control of grain size and grain size distribution.}, number={5}, journal={SCRIPTA MATERIALIA}, author={Zhu, XK and Zhang, X and Wang, H and Sergueeva, AV and Mukherjee, AK and Scattergood, RO and Narayan, J and Koch, CC}, year={2003}, month={Sep}, pages={429–433} }
 @article{wang_gupta_tiwari_zhang_narayan_2003, title={TaN-TiN binary alloys and superlattices as diffusion barriers for copper interconnects}, volume={32}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-003-0081-7}, number={10}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Wang, H and Gupta, A and Tiwari, A and Zhang, X and Narayan, J}, year={2003}, month={Oct}, pages={994–999} }
 @article{wang_tiwari_zhang_kvit_narayan_2002, title={Copper diffusion characteristics in single-crystal and polycrystalline TaN}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1502193}, abstractNote={We have investigated the diffusivity of copper in single-crystal (NaCl-structured) and polycrystalline TaN thin films grown by pulsed-laser deposition. Polycrystalline TaN films were grown directly on Si(100), while single-crystal films were grown with TiN buffer layers. Both poly- and single-crystal films with Cu overlayers were annealed at 500, 600, 650, and 700 °C in vacuum to study the copper diffusion characteristics. The diffusion of copper into TaN was studied using scanning transmission electron microscopy (STEM) Z contrast, where the contrast is proportional to Z2 (atomic number), and TEM. The diffusion distances (2Dτ) are found to be about 5 nm at 650 °C for 30 min annealing. The diffusivity of Cu into single-crystal TaN follows the relation D=(160±9.5)exp[−(3.27±0.1)eV/kB T] cm2 s−1 in the temperature range of 600–700 °C. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Wang, H and Tiwari, A and Zhang, X and Kvit, A and Narayan, J}, year={2002}, month={Aug}, pages={1453–1455} }
 @article{narayan_larson_2003, title={Domain epitaxy: A unified paradigm for thin film growth}, volume={93}, ISSN={["1089-7550"]}, DOI={10.1063/1.1528301}, abstractNote={We present a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME). The DME involves matching of lattice planes between the film and the substrate having similar crystal symmetry. In this framework, the conventional lattice matching epitaxy becomes a special case where a matching of lattice constants or the same planes is involved with a small misfit of less than 7%–8%. In large lattice mismatch systems, we show that epitaxial growth of thin films is possible by matching of domains where integral multiples of major lattice planes match across the interface. We illustrate this concept with atomic-level details in the TiN/Si(100) with 3/4 matching, the AlN/Si(100)with 4/5 matching, and the ZnO/α−Al2O3(0001) with 6/7 matching of major planes across the film/substrate interface. By varying the domain size, which is equal to intregral multiple of lattice planes, in a periodic fashion, it is possible to accommodate additional misfit beyond perfect domain matching. Thus, we can potentially design epitaxial growth of films with any lattice misfit on a given substrate with atomically clean surfaces. In situ x-ray diffraction studies on initial stages of growth of ZnO films on sapphire correctly identify a compressive stress and a rapid relaxation within 1 to 2 monolayers, consistent with the DME framework and the fact that the critical thickness is less than 1 monolayer. DME examples ranging from the Ge–Si/Si(100) system with 49/50 matching (2% strain) to metal/Si systems with 1/2 matching (50% strain) are tabulated, strategies for growing strain-free films by engineering the misfit to be confined near the interface are presented, and the potential for epitaxial growth of films with any lattice misfit on a given substrate with atomically clean surfaces is discussed.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Narayan, J and Larson, BC}, year={2003}, month={Jan}, pages={278–285} }
 @article{narayan_wang_ye_hon_fox_chen_choi_fan_2002, title={Effect of thickness variation in high-efficiency InGaN/GaN light-emitting diodes}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1496145}, abstractNote={In x Ga (1−x) N/GaN multiquantum-well light-emitting diodes (LEDs) having periodic thickness variations (TVs) in InxGa(1−x)N active layers exhibit substantially higher optical efficiency than LEDs with uniform InxGa(1−x)N layers. In these nanostructured LEDs, the thickness variation of the active layers is found to be more important than the In composition fluctuation in quantum confinement of excitons (carriers). Detailed scanning transmission electron microscopy-atomic number Z contrast analysis, where image contrast is proportional to Z2 (Z being the atomic number), was carried out to investigate the variation in thickness as well as the spatial distribution of In. In the nanostructured LEDs, there are short-range thickness variations (SR-TVs) (3–4 nm) and long-range thickness variations (LR-TVs) (50–100 nm) in InxGa(1−x)N layers. It is envisaged that LR-TV is key to quantum confinement of the carriers and enhancement of the optical efficiency. We propose that the LR-TV is caused by two-dimensional strain in the InxGa(1−x)N layer below its critical thickness. The SR-TV may be caused by In composition fluctuation.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Narayan, J and Wang, H and Ye, JL and Hon, SJ and Fox, K and Chen, JC and Choi, HK and Fan, JCC}, year={2002}, month={Jul}, pages={841–843} }
 @article{wang_tiwari_kvit_zhang_narayan_2002, title={Epitaxial growth of TaN thin films on Si(100) and Si(111) using a TiN buffer layer}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1466522}, abstractNote={We have deposited high-quality epitaxial B1 NaCl-structured TaN films on Si(100) and Si(111) substrates with TiN as the buffer layer, using pulsed laser deposition. Our method exploits the concept of lattice-matching epitaxy between TiN and TaN and domain-matching epitaxy between TiN and silicon. X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy (Z-contrast) experiments confirmed the single-crystalline nature of the films with cube-on-cube epitaxy. The stoichiometry of the TaN films was determined to be nitrogen deficient (TaN0.95±0.05) by Rutherford backscattering. Resistivity of the TaN films was found to be ∼220 μΩ cm at room temperature with a temperature coefficient of resistivity of −0.5 μΩ K−1.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Wang, H and Tiwari, A and Kvit, A and Zhang, X and Narayan, J}, year={2002}, month={Apr}, pages={2323–2325} }
 @article{tiwari_park_jin_wang_kumar_narayan_2002, title={Epitaxial growth of ZnO films on si(111)}, volume={17}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.2002.0361}, abstractNote={In this paper, we report the growth of ZnO films on silicon substrates using a pulsed laser deposition technique. These films were deposited on Si(111) directly as well as by using thin buffer layers of AlN and GaN. All the films were found to have c-axis-preferred orientation aligned with normal to the substrate. Films with AlN and GaN buffer layers were epitaxial with preferred in-plane orientation, while those directly grown on Si(111) were found to have random in-plane orientation. A decrease in the frequency of the  Raman mode and a red shift of the band-edge photoluminescence peak due to the presence of tensile strain in the film, was observed. Various possible sources for the observed biaxial strain are discussed.}, number={10}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Tiwari, A and Park, M and Jin, C and Wang, H and Kumar, D and Narayan, J}, year={2002}, month={Oct}, pages={2480–2483} }
 @article{zhang_wang_scattergood_narayan_koch_2003, title={Evolution of microstructure and mechanical properties of in situ consolidated bulk ultra-fine-grained and nanocrystalline Zn prepared by ball milling}, volume={344}, ISSN={["0921-5093"]}, DOI={10.1016/s0921-5093(02)00422-7}, abstractNote={The evolution of the microstructure and mechanical properties of ultra-fine-grained and nanocrystalline Zn induced by ball milling at room temperature are studied systematically. The yield stresses measured from miniaturized disk bend tests and tensile tests are consistent with the microhardness results and generally increase with the decrease of average grain size. A dramatic decrease of hardness during milling from 1 to 3 h is a reflection of the increase of average grain size from 80 to 240 nm due to the initial unstable grain size and therefore, grain growth in this period. Young's modulus remains almost the same for samples milled for different times and is that for conventional grain size Zn. A transition from bending to membrane stretching is observed in the force–displacement curves for Zn ball milled for ≤18 h. The variation of transition strain with milling time could be related to the evolution of grain size distribution and therefore hardness during milling.}, number={1-2}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Zhang, X and Wang, H and Scattergood, RO and Narayan, J and Koch, CC}, year={2003}, month={Mar}, pages={175–181} }
 @article{narayan_wang_oh_choi_fan_2002, title={Formation of epitaxial Au/Ni/Au ohmic contacts to p-GaN}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1524032}, abstractNote={We have designed a promising contact scheme to p-GaN, where Au/Ni/Au layers are deposited on p-GaN and annealed in air for 30 min at 470 °C to produce low-resistivity ohmic contacts. The Au layer in contact with p-GaN grows epitaxially via domain matching epitaxy, which acts as a template for NiO growth via lattice matching epitaxy. The 〈111〉 oriented gold rotates 30° in the basal (0001) plane of GaN by 30° with the following orientation relationship: [111]Au//[0001]GaN; [112̄]Au//[21̄1̄0]GaN. As a result, we can create epitaxial NiO–Au composite, where Au as well as NiO are in contact with p-GaN. This epitaxial composite structure is envisaged to be important in achieving low-resistivity ohmic contacts in p-GaN. We present the details of atomic structure, epitaxial relationship, chemistry, and electrical properties of ohmic contacts.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Narayan, J and Wang, H and Oh, TH and Choi, HK and Fan, JCC}, year={2002}, month={Nov}, pages={3978–3980} }
 @article{narayan_oktyabrsky_2002, title={Formation of misfit dislocations in thin film heterostructures}, volume={92}, ISSN={["0021-8979"]}, DOI={10.1063/1.1521789}, abstractNote={We have studied characteristics of 60° and 90° dislocations in GaAs/Si(100) thin-film heterostructures grown by metal-organic chemical-vapor deposition at 650 °C. The misfit dislocation network consists of approximately 60% of 90° dislocations, and 40% of the closely spaced pairs of 60° dislocations with intersecting glide planes. This ratio has remained essentially constant after rapid thermal annealing at 800 °C for 90 sec. It is envisaged that these 60° dislocation pairs have parallel screw components and as a result they cannot combine to form a 90° dislocation. Upon annealing, some of the 60° dislocation pairs split to form stacking faults in agreement with our earlier model. Based upon these observations, we propose a model where a first set of 60° dislocations is generated from the undulated surface above a critical thickness. The second set of 60° dislocations is nucleated at a larger thickness and at the smoother surface. The Burgers vectors of these dislocations are controlled by the dislocations from the first set, and only low-energy dislocation pairs are formed through glide towards the interface and later through short glide and climb along the interface plane. We have used a numerical analysis based on elasticity theory to evaluate the changes in the nucleation barrier for the 60° dislocations caused by the interaction with the existing misfit dislocations.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Narayan, J and Oktyabrsky, S}, year={2002}, month={Dec}, pages={7122–7127} }
 @article{tiwari_narayan_jin_kvit_2002, title={Growth of epitaxial NdNiO3 and integration with Si(100)}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1451984}, abstractNote={We have grown epitaxial NdNiO3 films on Si(100) substrate under ambient oxygen pressure using a pulsed-laser deposition method. The integration of NdNiO3 with Si(100) was accomplished by lattice-matching epitaxy of MgO and SrTiO3 and domain matching epitaxy of TiN on Si(100). During domain matching epitaxy, four lattice constants of TiN match with three of silicon across the TiN/Si(100) interface. High-quality epitaxial NdNiO3 film on SrTiO3/MgO/TiN/Si(100) showed a very sharp metal–insulator (MI) phase transition at 200 K. Observed MI transition in epitaxial NdNiO3 is much sharper than that usually observed in bulk and polycrystalline films with more than four orders of magnitude change in resistivity. This MI transition is understood to arise because of the opening of charge transfer gap between Ni3+(3d) and O2−(2p) band.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Tiwari, A and Narayan, J and Jin, C and Kvit, A}, year={2002}, month={Feb}, pages={1337–1339} }
 @article{kumar_zhou_nath_kvit_narayan_craciun_singh_2002, title={Improved magnetic properties of self-assembled epitaxial nickel nanocrystallites in thin-film ceramic matrix}, volume={17}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.2002.0107}, abstractNote={Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles was investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in the case of the TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in the Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization–field (M–H) hysteretic behavior, of the Ni–TiN sample (approximately 190 K) is significantly higher than that of Ni–Al2O3 sample (approximately 30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles in amorphous alumina matrix. The high values of TB and Hc of Ni–TiN samples with respect to TB of N–A12O3 samples are believed to be associated with preferred alignment of nanocrystallites.}, number={4}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Kumar, D and Zhou, H and Nath, TK and Kvit, AV and Narayan, J and Craciun, V and Singh, RK}, year={2002}, month={Apr}, pages={738–742} }
 @article{tiwari_chug_jin_kumar_narayan_2002, title={Integration of single crystal La0.7Sr0.3MnO3 films with Si(001)}, volume={121}, ISSN={["0038-1098"]}, DOI={10.1016/S0038-1098(02)00029-7}, abstractNote={We have successfully grown high quality epitaxial La0.7Sr0.3MnO3 (LSMO) films on Si(001) substrate using TiN/MgO/SrTiO3 buffer layers by a pulsed laser deposition technique. The integration of LSMO with Si(100) was realized by domain matching epitaxy of TiN on Si(001) and lattice matching epitaxy of MgO, SrTiO3 and LSMO. During domain matching epitaxy, four lattice constants of TiN match with three of silicon across the TiN/Si(001) interface. X-ray diffraction and transmission electron microscope investigations showed the films to be single phase, single crystalline and epitaxial with (001) orientation. Electrical resistivity measurements showed a metal–insulator transition with a resistivity peak at ∼305 K. Enhanced electron–electron interactions are found to play significant role in LSMO films at low temperatures.}, number={12}, journal={SOLID STATE COMMUNICATIONS}, author={Tiwari, A and Chug, A and Jin, C and Kumar, D and Narayan, J}, year={2002}, pages={679–682} }
 @article{tiwari_rajeev_narayan_2002, title={Low temperature electrical transport in La1-xNdxNiO3-delta}, volume={121}, DOI={10.1016/s0038-1098(02)00007-8}, abstractNote={We have investigated low temperature electrical transport in La1−xNdxNiO3−δ perovskite oxide samples. Samples were prepared by a sol–gel method and were characterized by X-ray diffraction and chemical methods. High precision electrical resistivity, magnetoresistance (MR) and electron tunneling conductance measurements were performed. Crystal structure investigations showed a phase transition from rhombohedral to orthorhombic phase at x=0.4. In the orthorhombic phase Ni–O–Ni bond angle was found to depend very sensitively on the value of x; as the value of x increases Ni–O–Ni bond angle decreases resulting in the tilting of NiO6 octahedra. A Correlation between the Ni–O–Ni bond angle and electrical transport has been observed. The analysis of the electrical resistivity data showed the presence of disorder driven quantum correction effects, namely e–e interactions and weak localization, in the system. A dip in the tunneling density of states and negative MR also suggest the presence of e–e interaction and weak localization effects in the system.}, number={6-7}, journal={Solid State Communications}, author={Tiwari, A. and Rajeev, K. P. and Narayan, Jagdish}, year={2002}, pages={357–361} }
 @article{kumar_sankar_narayan_singh_majumdar_2002, title={Low-temperature resistivity minima in colossal magnetoresistive La0.7Ca0.3MnO3 thin films}, volume={65}, number={9}, journal={Physical Review. B, Condensed Matter and Materials Physics}, author={Kumar, D. and Sankar, J. and Narayan, J. and Singh, R. K. and Majumdar, A. K.}, year={2002}, pages={094407–1} }
 @article{zhang_wang_scattergood_narayan_koch_2002, title={Mechanical properties of cyromilled nanocrystalline Zn studied by the miniaturized disk bend test}, volume={50}, ISSN={["1359-6454"]}, DOI={10.1016/S1359-6454(02)00176-3}, abstractNote={The miniaturized disk bend test (MDBT) is useful for the study of the mechanical properties of small specimens in tension. The yield stress of cryomilled nanocrystalline Zn measured by MDBT shows periodic hardening and softening with milling time, consistent with the variation of microhardness with milling time. The periodic softening is due to the reduction of dislocation density controlled by dynamic recrystallization. The ductility of these softened nanocrystalline Zn specimens is consistently higher than that of the hardened specimens. Young’s modulus shows little variation with the average grain size.}, number={13}, journal={ACTA MATERIALIA}, author={Zhang, X and Wang, H and Scattergood, RO and Narayan, J and Koch, CC}, year={2002}, month={Aug}, pages={3527–3533} }
 @article{conrad_narayan_2002, title={Mechanism for grain size softening in nanocrystalline Zn}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1507353}, abstractNote={A technique (laser deposition of Zn/W multilayers) for producing stable nanocrystalline (nc) Zn films free of undesirable imperfections down to a grain size of d=6 nm is presented. These films exhibited grain size softening (inverse Hall–Petch effect) for d⩽11 nm, providing support that this can be a real phenomenon in nc solids. The mechanism responsible for the softening was concluded to be thermally activated grain boundary shear.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Conrad, H and Narayan, J}, year={2002}, month={Sep}, pages={2241–2243} }
 @article{conrad_narayan_2002, title={Mechanisms for grain size hardening and softening in Zn}, volume={50}, ISSN={["1873-2453"]}, DOI={10.1016/S1359-6454(02)00357-9}, abstractNote={An analysis of the rate-controlling mechanisms corresponding to effect of grain size d=10−9 to 10−3 m on the flow stress of Zn at 300K and ϵ̇=10-4-10-3 s−1 was performed. Three grain size regimes were indicated: Regime I, d≈10−6–10−3 m, Regime II, d≈10−6–10−8 m and Regime III, d<10−8 m. Grain size hardening occurred in Regimes I and II and grain size softening in Regime III. The intersection of pyramidal forest dislocations by basal dislocations was concluded to be the rate-controlling mechanism in both Regimes I and II, the major effect of the grain size being on the forest and gliding dislocation densities. The absence of twinning and a dislocation cell structure distinguished Regime II from I. The grain size softening observed in Regime III is in better accord with grain boundary shear than with grain boundary diffusion creep.}, number={20}, journal={ACTA MATERIALIA}, author={Conrad, H and Narayan, J}, year={2002}, month={Dec}, pages={5067–5078} }
 @article{zhang_wang_scattergood_narayan_koch_2002, title={Modulated oscillatory hardening and dynamic recrystallization in cryomilled nanocrystalline Zn}, volume={50}, ISSN={["1359-6454"]}, DOI={10.1016/S1359-6454(02)00199-4}, abstractNote={Abstract Oscillatory variation of the hardness with milling time was observed in cryomilled nanocrystalline Zn. Transmission electron microscopy showed that large variations in the dislocation density and grain-size distribution occurred during cryomilling. The observations suggest that recrystallization takes place in larger grains when the dislocation density due to strain-hardening reaches a critical level. A reaction-rate model was developed which accounts for the dynamic recrystallization effect and the observed oscillations in hardness. Good agreement was obtained with the experimental data. The results provide unique insight into grain-size effects and the interplay of these with deformation mechanisms and recrystallization effects in nanocrystalline materials.}, number={16}, journal={ACTA MATERIALIA}, author={Zhang, X and Wang, H and Scattergood, RO and Narayan, J and Koch, CC}, year={2002}, month={Sep}, pages={3995–4004} }
 @article{narayan_sharma_kvit_jin_muth_holland_2002, title={Novel cubic ZnxMg1-xO epitaxial hetero structures on Si (100) substrates}, volume={121}, number={1}, journal={Solid State Communications}, author={Narayan, J. and Sharma, A. K. and Kvit, A. and Jin, C. and Muth, J. F. and Holland, O. W.}, year={2002}, pages={9–13} }
 @article{zhang_wang_kassem_narayan_koch_2002, title={Preparation of bulk ultrafine-grained and nanostructured Zn, Al and their alloys by in situ consolidation of powders during mechanical attrition}, volume={46}, ISSN={["1359-6462"]}, DOI={10.1016/S1359-6462(02)00048-9}, abstractNote={Bulk ultrafine-grained (UFG) or nanostructured Zn, Al and their alloys were produced via in situ consolidation of powders by mechanical attrition (MA) at room temperature. In situ consolidation of metal powders during MA may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination.}, number={9}, journal={SCRIPTA MATERIALIA}, author={Zhang, X and Wang, H and Kassem, M and Narayan, J and Koch, CC}, year={2002}, month={May}, pages={661–665} }
 @article{tiwari_jin_narayan_2002, title={Strain-induced tuning of metal-insulator transition in NdNiO3}, volume={80}, ISSN={["1077-3118"]}, DOI={10.1063/1.1480475}, abstractNote={We have used the lattice-mismatch epitaxial strain, induced by the constraint of epitaxy, to tune the metal–insulator (M–I) transition temperature of NdNiO3 films grown on Si(100) substrate. Films were integrated with the Si(100) substrate using several combinations of thin buffer layers. A systematic variation in the electrical transport properties has been observed with the change in the lattice mismatch between NdNiO3 and the buffer layer just below it. It was shown that by the proper selection of the substrate and thickness of film, it is possible to control and precisely tune the M–I transition temperature of NdNiO3 to any desired value between 12 and 300 K (temperature range of this study). Fine control over the M–I transition temperature of these films is likely to boost the potential of these films for their applications in bolometers, actuators, and thermal/optical switches in next-generation perovskite-based microelectronic devices.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Tiwari, A and Jin, C and Narayan, J}, year={2002}, month={May}, pages={4039–4041} }
 @article{tiwari_jin_kvit_kumar_muth_narayan_2002, title={Structural, optical and magnetic properties of diluted magnetic semiconducting Zn1-xMnxO films}, volume={121}, ISSN={["0038-1098"]}, DOI={10.1016/S0038-1098(01)00464-1}, abstractNote={We have investigated the structural, optical and magnetic properties of high quality epitaxial Zn1−xMnxO (diluted magnetic semiconductor) films. These films were deposited on (0001) sapphire substrate by a pulsed laser deposition technique. The nonequilibrium nature of the laser–material interaction allowed us to dope higher Mn contents (x=0.36) than allowed by thermal equilibrium limit (x∼0.13). All the films investigated here were found to be single phased and epitaxial with (0001) orientation. As the Mn concentration increases in the system, the c-axis lattice constant was found to increase linearly. Optical transmittance study showed an increase in the insulating band-gap (Eg) with increase in Mn atomic fraction x following Eg=3.270+2.760x−4.988x2eV. DC magnetization measurements showed the paramagnetic nature of the system.}, number={6-7}, journal={SOLID STATE COMMUNICATIONS}, author={Tiwari, A and Jin, C and Kvit, A and Kumar, D and Muth, JF and Narayan, J}, year={2002}, pages={371–374} }
 @article{narayan_venkatesan_kvit_2002, title={Structure and properties of nanocrystalline zinc films}, volume={4}, ISSN={["1572-896X"]}, DOI={10.1023/A:1019925315398}, number={3}, journal={JOURNAL OF NANOPARTICLE RESEARCH}, author={Narayan, J and Venkatesan, RK and Kvit, A}, year={2002}, month={Jun}, pages={265–269} }
 @article{zhang_wang_scattergood_narayan_koch_sergueeva_mukherjee_2002, title={Studies of deformation mechanisms in ultra-fine-grained and nanostructured Zn}, volume={50}, ISSN={["1359-6454"]}, DOI={10.1016/S1359-6454(02)00349-X}, abstractNote={The temperature, strain rate, grain size and grain size distribution effects on plastic deformation in ultra-fine-grained (UFG) and nanocrystalline Zn are systematically studied. The decrease of ductility with the decrease of average grain size could be an inherent effect in nanocrystalline materials, that is, not determined by processing artifacts. The superior ductility observed in UFG Zn may originate from both dislocation creep within large grains and grain boundary sliding of small nanograins. The stress exponent for dislocation creep is about 6.6. The activation energy for plastic deformation in UFG Zn is close to the activation energy for grain boundary self diffusion in pure Zn.}, number={19}, journal={ACTA MATERIALIA}, author={Zhang, X and Wang, H and Scattergood, RO and Narayan, J and Koch, CC and Sergueeva, AV and Mukherjee, AK}, year={2002}, month={Nov}, pages={4823–4830} }
 @article{kumar_pennycook_lupini_duscher_tiwari_narayan_2002, title={Synthesis and atomic-level characterization of Ni nanoparticles in Al2O3 matrix}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1525052}, abstractNote={Single domain magnetic nickel nanocrystals were embedded in alumina matrix using a pulsed-laser deposition technique. Structural characterization carried out at the atomic level using scanning transmission electron microscopy with atomic number contrast (STEM-Z) in conjunction with electron energy loss spectroscopy have revealed that the Ni particles are well separated and have interfaces with the host matrix that are atomically sharp and free of any oxide layer. An excellent correlation was found between particle sizes determined theoretically from magnetization versus field data and experimentally using STEM-Z which indicates the absence of any magnetically dead layers on the Ni nanoparticles within an experimental error of 0.1 monolayer.}, number={22}, journal={APPLIED PHYSICS LETTERS}, author={Kumar, D and Pennycook, SJ and Lupini, A and Duscher, G and Tiwari, A and Narayan, J}, year={2002}, month={Nov}, pages={4204–4206} }
 @article{zhang_wang_scattergood_narayan_koch_sergueeva_mukherjee_2002, title={Tensile elongation (110%) observed in ultrafine-grained Zn at room temperature}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1494866}, abstractNote={Tensile tests were performed for Zn at room temperature, which show elongations of 110%–20% for average grain sizes of 240–23 nm, respectively. The ductility of ultrafine-grained and nanocrystalline Zn was found to decrease with grain size refinement. The deformation mechanisms in ultrafine-grained Zn are believed to be a mixture of grain boundary sliding of small nanograins and intra-grain dislocation creep within the large grains.}, number={5}, journal={APPLIED PHYSICS LETTERS}, author={Zhang, X and Wang, H and Scattergood, RO and Narayan, J and Koch, CC and Sergueeva, AV and Mukherjee, AK}, year={2002}, month={Jul}, pages={823–825} }
 @article{tiwari_wang_kumar_narayan_2002, title={Weak-localization effect in single crystal TaN(001) films}, volume={16}, ISSN={["0217-9849"]}, DOI={10.1142/s0217984902004688}, abstractNote={ We here report the manifestation of weak localization effects in the electrical resistivity of TaN (001) films grown on MgO (001) substrates by a pulsed laser deposition technique. These films were characterized by X-ray diffraction and Rutherford backscattering. High precision electrical resistivity measurements were performed on these films in the temperature range 12–300 K. A careful analysis of data showed these films to lie in the weakly localized regime with negative temperature coefficient of resistivity throughout the whole temperature range of study. A crossover from 2D localization at lower temperatures to 3D localization at higher temperatures was observed. }, number={28-29}, journal={MODERN PHYSICS LETTERS B}, author={Tiwari, A and Wang, H and Kumar, D and Narayan, J}, year={2002}, month={Dec}, pages={1143–1149} }
 @article{lopatin_pennycook_narayan_duscher_2002, title={Z-contrast imaging of dislocation cores at the GaAs/Si interface}, volume={81}, ISSN={["0003-6951"]}, DOI={10.1063/1.1511808}, abstractNote={The interface between silicon and epitaxial GaAs thin film grown by metalorganic chemical vapor deposition was studied using atomic-resolution Z-contrast imaging. Z-contrast imaging provides chemical composition information and allows direct interpretation of micrographs without simulation. Three different types of dislocations were identified. As expected, a dangling bond was found in the atomic structure of the 60° dislocation. One of the observed 90° dislocations had the reconstructed atomic core structure (with no dangling bonds). The core structure of the other 90° dislocation exhibited a dangling bond.}, number={15}, journal={APPLIED PHYSICS LETTERS}, author={Lopatin, S and Pennycook, SJ and Narayan, J and Duscher, G}, year={2002}, month={Oct}, pages={2728–2730} }
 @article{sharma_kalyanaraman_narayan_oktyabrsky_narayan_2001, title={Carbon nanotube composites synthesized by ion-assisted pulsed laser deposition}, volume={79}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(00)00558-4}, abstractNote={We have synthesized thin CNx films on Si (100) substrate at high temperatures (600 and 700°C) by nitrogen ion-assisted pulsed laser deposition (PLD). The bonding characteristics and microstructure determinations have been accomplished using X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), respectively. The radial distribution function (RDF) analysis of the electron diffraction patterns was performed to determine the short range atomic order in these films. The results reveal the presence of carbon predominantly in the trigonally-coordinated state with small fractions of nitrogen (upto 20 at.%) bonded to carbon. The electron diffraction and the high resolution images in cross-section view reveal that there is a textured growth of nanotube or graphite-like ribbons. The plan-view specimens show high resolution images with bended layers similar to that of onion or nanotube like features. The kinetics of the ions assisting the growth is assumed to be important to grow the basal planes (00l) of graphite perpendicular to the substrate. The large anisotropic surface energies in two perpendicular directions in graphite suggest that ions can create nonequilibrium conditions to alter the growth mode of graphitic planes. The importance of ion-assisted PLD to grow novel nanotube or fullerenelike structure in the form of thin film composites for electron field emission devices is emphasized.}, number={2}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Sharma, AK and Kalyanaraman, R and Narayan, RJ and Oktyabrsky, S and Narayan, J}, year={2001}, month={Jan}, pages={123–127} }
 @article{wei_sankar_sharma_yamagata_narayan_2001, title={Effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon films prepared by pulsed laser deposition}, volume={19}, ISSN={["0734-2101"]}, DOI={10.1116/1.1322641}, abstractNote={We have investigated the effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon thin films prepared by pulsed laser deposition. The amorphous carbon films were deposited in various atmospheres such as nitrogen and argon at different chamber pressures. We used Raman spectroscopy to study the bonding characteristics of the deposited amorphous carbon films. Atomic force microscopy and optical microscopy were utilized to observe the surface conditions and the microstructures of the deposited films. Nanoindentation measurements were carried out on various samples prepared under different conditions to study the effect of chamber pressure and atmosphere on the elastic modulus and nanohardness of the films. It was found that reduced vacuum leads to formation of amorphous carbon films with reduced elastic modulus and nanohardness. Amorphous carbon films prepared under higher chamber pressures exhibit an increased density of particulates and significantly roughened surface. The results were understood in combination with the optical emission and electrostatic measurements of the laser plasma plume. It was found that the presence of atmosphere decreases the leading edge ionic energies of the species in the laser plasma plume and increases the thermalization of the laser plasma due to an increased possibility of collision.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Wei, Q and Sankar, J and Sharma, AK and Yamagata, Y and Narayan, J}, year={2001}, pages={311–316} }
 @article{zhang_wang_narayan_koch_2001, title={Evidence for the formation mechanism of nanoscale microstructures in cryomilled Zn powder}, volume={49}, ISSN={["1873-2453"]}, DOI={10.1016/S1359-6454(01)00051-9}, abstractNote={Nanocrystalline Zn powder has been synthesized by a cryomilling method. The average grain size decreased exponentially with the cryomilling time and reached a minimum average grain size of around 17 nm. Large numbers of small grains (2∼6 nm) have been found in the very early stages of cryomilling. Dynamic recrystallization was used to explain the observed phenomena. The exothermic peaks revealed in the differential scanning calorimetry (DSC) results were correlated with the release of microstrain as confirmed by the x-ray diffraction measurements.}, number={8}, journal={ACTA MATERIALIA}, author={Zhang, X and Wang, H and Narayan, J and Koch, CC}, year={2001}, month={May}, pages={1319–1326} }
 @article{kumar_narayan_kvit_sharma_sankar_2001, title={High coercivity and superparamagnetic behavior of nanocrystalline iron particles in alumina matrix}, volume={232}, ISSN={["1873-4766"]}, DOI={10.1016/S0304-8853(01)00191-3}, abstractNote={Single-domain nanoscale magnetic iron particles have been embedded uniformly in an amorphous matrix of alumina using a pulsed laser deposition technique. Structural characterization by transmission electron microscopy (TEM) reveals the presence of a crystalline iron and an amorphous alumina phase. Fine particle magnetism have been investigated by carrying out field and temperature dependence of magnetization measurements using superconducting quantum interference device magnetometer. The particle size of Fe in Al2O3 matrices prepared by changing the deposition time of Fe, have been found to be 9, 7 and 5 nm from TEM studies. At 10 K, the coercivities of these samples are found be 450, 350 and 150 Oe, respectively. At 300 K, the coercivity of Fe–Al2O3 sample decreases from 100 to 50 Oe as the particle size decreases from 9 to 7 nm and finally the sample turns superparamagnetic when the Fe particle size becomes around 5 nm. Based on the calculated value of blocking temperature, TB, (481 K), magnetic anisotropy K (4.8×105 erg/cm3) for Fe, and the Boltzmann constant kB (1.38×10−16 erg/K) from TB=KV/25kB, the mean radius of Fe particles is found to be 9.3 nm. in one of the samples. This is in good agreement with the particle size measured using TEM studies.}, number={3}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Kumar, D and Narayan, J and Kvit, AV and Sharma, AK and Sankar, J}, year={2001}, month={Jul}, pages={161–167} }
 @article{chattopadhyay_kvit_kumar_sharma_sankar_narayan_knight_coleman_lee_2001, title={Low temperature synthesis and electrical properties of epitaxial Sr0.8Bi2.2Ta2O9 thin films}, volume={78}, DOI={10.1063/1.1374226}, abstractNote={High quality epitaxial thin films of Sr0.8Bi2.2Ta2O9 (SBT) were grown on LaNiO3 (LNO) bottom electrodes. The SBT/LNO heterostructure was fabricated on (001) oriented LaAlO3 substrates by pulsed laser ablation. X-ray diffraction and high resolution transmission electron microscopy revealed epitaxial growth of SBT and LNO layers along the (001) direction and sharp interfaces between the epilayers. The SBT films exhibited a dielectric constant of ∼270 and the loss tangent varied from 0.02 to 0.04. The dielectric constant measured as a function of bias field revealed that the films were not ferroelectric in nature. The room temperature frequency response of the dielectric constant was observed to obey Curie–von Schweidler power law with an exponent of 0.02 in the range of 10 kHz–1 MHz.}, number={22}, journal={Applied Physics Letters}, author={Chattopadhyay, Soma and Kvit, A. and Kumar, Dhananjay and Sharma, A.K. and Sankar, Jagannathan and Narayan, Jagdish and Knight, V.S. and Coleman, T.S. and Lee, Clinton B.}, year={2001}, month={May}, pages={3514–3516} }
 @article{katiyar_kumar_nath_kvit_narayan_chattopadhyay_gilmore_coleman_lee_sankar_et al._2001, title={Magnetic properties of self-assembled nanoscale La2/3Ca1/3MnO3 particles in an alumina matrix}, volume={79}, ISSN={["0003-6951"]}, DOI={10.1063/1.1399001}, abstractNote={We have investigated the processing and properties of La2/3Ca1/3MnO3 self-assembled nanodots formed in a nonmagnetic alumina matrix, which were produced by a pulsed-laser deposition process. The size of the nanodots was found to be in the range of 10–15 nm using high-resolution transmission electron microcopy. The average interlayer separation between two dots has been found to be 2–5 nm, which is sufficient to decouple the magnetic grains. The decoupling of the grains is supported by the zero-field-cooled and field-cooled magnetization (M) data. The coercivity of the La2/3Ca1/3MnO3 nanodots has been measured using magnetization measurements as a function of field (H) at different temperatures above and below the blocking temperature of the samples. The coercivity is found to vary from 600 Oe at 10 K to 400 and 200 Oe at 20 and 50 K, respectively. Above the blocking temperature, the sample is found to transform to a superparamagnetic magnetic state, resulting in the disappearance of any hysteresis in the M–H loops.}, number={9}, journal={APPLIED PHYSICS LETTERS}, author={Katiyar, P and Kumar, D and Nath, TK and Kvit, AV and Narayan, J and Chattopadhyay, S and Gilmore, WM and Coleman, S and Lee, CB and Sankar, J and et al.}, year={2001}, month={Aug}, pages={1327–1329} }
 @article{wang_sharma_kvit_wei_zhang_koch_narayan_2001, title={Mechanical properties of nanocrystalline and epitaxial TiN films on (100) silicon}, volume={16}, ISSN={["2044-5326"]}, DOI={10.1557/JMR.2001.0373}, abstractNote={We investigated mechanical properties of TiN as a function of microstructure varying from nanocrystalline to single crystal TiN films deposited on (100) silicon substrates. By varying the substrate temperature from 25 to 700 °C during pulsed laser deposition, the microstructure of TiN films changed from nanocrystalline (having a uniform grain size of 8 nm) to a single crystal epitaxial film on the silicon (100) substrate. The microstructure and epitaxial nature of these films were investigated using x-ray diffraction and high-resolution transmission electron microscopy. Hardness measurements were made using nanoindentation techniques. The nanocrystalline TiN contained numerous triple junctions without any presence of amorphous regions. The width of the grain boundary remained constant at less than 1 nm as a function of boundary angle. Similarly the grain boundary structure did not change with grain size. The hardness of TiN films decreased with decreasing grain size. This behavior was modeled recently involving grain boundary sliding, which is particularly relevant in the case of hard materials such as TiN.}, number={9}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Wang, H and Sharma, A and Kvit, A and Wei, Q and Zhang, X and Koch, CC and Narayan, J}, year={2001}, month={Sep}, pages={2733–2738} }
 @article{wei_sankar_narayan_2001, title={Microstructural changes due to heat-treatment of annealing and their effect on the creep behavior of self-reinforced silicon nitride ceramics}, volume={299}, ISSN={["0921-5093"]}, DOI={10.1016/s0921-5093(00)01403-9}, abstractNote={In order to understand the improvement of creep resistance by furnace and microwave annealing, we have investigated the effect of heat-treatment on the microstructural characteristics of the crept self-reinforced silicon nitride (Si3N4) ceramic GS44. X-ray diffraction was performed on the as-sintered and heat-treated samples to study the phase changes due to annealing treatment. Optical microscopy and scanning electron microscopy (SEM) were used to study the fracture surface and to identify the creep mechanism. High resolution and analytical transmission electron microscopy (TEM) were employed to analyze the microstructures of the crept samples with as-received and heat-treated conditions. It has been reported that both conventional furnace and microwave annealing enhance the creep resistance of the material, and microwave annealing had the most significant effect. Fractography showed that the microwave annealed samples exhibits least creep damage. Furnace annealing also reduces the creep damage, but the effect is far less as compared to microwave annealing. Scanning electron microscopy (SEM) analysis showed significant amount of multiple-junction cavitation in the creep-tested samples. TEM observations showed significant devitrification of the amorphous phases in the microwave annealed specimens, as verified by micro-diffraction studies of the junction phases. This is also confirmed by X-ray diffraction and high-resolution lattice image of the triple junction phases. The microstructural observations were combined with a recent model of the effect of amorphous residues in ceramics on the creep behavior to explain the improvement in the creep resistance due to annealing.}, number={1-2}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Wei, Q and Sankar, J and Narayan, J}, year={2001}, month={Feb}, pages={141–151} }
 @article{zhang_wang_kassem_narayan_koch_2001, title={Origins of stored enthalpy in cryomilled nanocrystalline Zn}, volume={16}, ISSN={["0884-2914"]}, DOI={10.1557/JMR.2001.0479}, abstractNote={Nanocrystalline Zn was prepared by cryomilling (mechanical attrition at liquid nitrogen temperature). Differential scanning calorimetry (DSC), x-ray diffraction, and transmission electron microscopy were used to study the structural changes and grain size distribution with milling time and subsequent annealing. Maxima in both stored enthalpy (for the low-temperature DSC peak) and lattice strain on the Zn basal planes were observed at the same milling time. Dislocation density on the basal planes is proposed as a major source for lattice strain and the measured stored enthalpy. The released enthalpy that might be due to grain growth is very small.}, number={12}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Zhang, XH and Wang, HY and Kassem, M and Narayan, J and Koch, CC}, year={2001}, month={Dec}, pages={3485–3495} }
 @article{kumar_zhou_nath_kvit_narayan_2001, title={Self-assembled epitaxial and polycrystalline magnetic nickel nanocrystallites}, volume={79}, DOI={10.1063/1.1412428}, abstractNote={Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed-laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles were investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in case of TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization-field (M–H) hysteretic behavior, of Ni–TiN sample (∼190 K) is significantly higher than that of Ni–Al2O3 sample (∼30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles. The high values of TB and Hc of Ni–TiN samples with respect to TB of Ni–Al2O3 samples are believed to be associated with preferred alignment of nanocrystallites.}, number={17}, journal={Applied Physics Letters}, author={Kumar, Dhananjay and Zhou, H. and Nath, T.K. and Kvit, Alex V. and Narayan, J.}, year={2001}, month={Oct}, pages={2817–2819} }
 @article{ikegami_ishibashi_yamagata_ebihara_thareja_narayan_2001, title={Spatial distribution of carbon species in laser ablation of graphite target}, volume={19}, ISSN={["1520-8559"]}, DOI={10.1116/1.1381403}, abstractNote={We report on the temporal evolution and spatial distribution of C2 and C3 molecules produced by KrF laser ablation of a graphite target using laser induced fluorescence imaging and optical emission spectroscopy. Spatial density profiles of C2 were measured using two-dimensional fluorescence in various pressures of different ambient (vacuum, nitrogen, oxygen, hydrogen, helium, and argon) gases at various ablation laser fluences and ablation area. A large yield of C2 is observed in the central part of the plume and near the target surface and its density and distribution was affected by the laser fluence and ambient gas. Fluorescent C3 was studied in Ar gas and the yield of C3 is enhanced at higher gas pressure and longer delay times after ablation.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Ikegami, T and Ishibashi, S and Yamagata, Y and Ebihara, K and Thareja, RK and Narayan, J}, year={2001}, pages={1304–1307} }
 @article{kumar_chattopadhyay_gilmore_lee_sankar_kvit_sharma_narayan_pietambaram_singh_et al._2001, title={Structural and magnetoresistance properties of La2/3Ca1/3MnO3 thin films on buffered silicon substrates}, volume={78}, ISSN={["0003-6951"]}, DOI={10.1063/1.1350603}, abstractNote={We report an epitaxial growth of LCMO (La2/3Ca1/3MnO3) film on Si by using a highly conducting diffusion barrier layer of TiN. In order to achieve epitaxial growth of LCMO films, MgO, and SrTiO3 films were used as intermediate layers between LCMO and TiN layers. The results have indicated that the properties of LCMO films on Si substrates, deposited under an optimized condition, are on par with the properties of LCMO films on conventional oxide substrates such as LaAlO3 and SrTiO3 in terms of paramagnetic to ferromagnetic transition temperature, insulator to metal transition temperature, and magnetoresistance ratio.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Kumar, D. and Chattopadhyay, S. and Gilmore, W. M. and Lee, C. B. and Sankar, J. and Kvit, A. and Sharma, A. K. and Narayan, Jagdish and Pietambaram, S. V. and Singh, R. K. and et al.}, year={2001}, month={Feb}, pages={1098–1100} }
 @article{wei_sankar_narayan_2001, title={Structure and properties of novel functional diamond-like carbon coatings produced by laser ablation}, volume={146}, ISSN={["0257-8972"]}, DOI={10.1016/S0257-8972(01)01394-9}, abstractNote={Diamond-like carbon (DLC) mainly consists of sp3 bonded carbon atoms. It can have properties that rival those of crystalline diamond. Its beneficial properties stem from the continuous rigid random networks of sp3 carbon atoms, and the properties can essentially be tailored by the sp3/sp2 ratio. DLC coatings or thin films can be prepared by pulsed laser ablation (PLA), filtered cathodic vacuum arc (FCVA) deposition and mass selected ion beam (MSIB) deposition. In the past decade, tremendous progress has been made in experimental and theoretical investigations of hydrogen-free DLC. Experimental and commercial applications in microelectronics, micro-tribology, biomedical technologies, etc., have been demonstrated. Potential applications include sensors, flat panel displays (field emitters), photodiode, etc. In this paper, we report comprehensively the past and recent efforts in the research of functional diamond-like carbon coatings prepared by pulsed laser ablation in our group. In order to alleviate the internal compressive stress problem associated with high quality DLC coatings, we have adopted a novel and simple target design. The films were characterized by Raman spectroscopy, transmission electron microscopy, IR range optical measurements, tribological measurement, etc.}, number={2001 Sep-Oct}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Wei, Q and Sankar, J and Narayan, J}, year={2001}, pages={250–257} }
 @article{misra_bist_navati_thareja_narayan_2001, title={Thin film of aluminum oxide through pulsed laser deposition: a micro-Raman study}, volume={79}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(00)00554-7}, abstractNote={Successful use of micro-Raman spectroscopy to characterize the surface of the thin Al2O3 films deposited on Si(010) substrate through pulsed laser ablation is presented. The micro-Raman spectra have been recorded on several spots (sized ≈1 μm) over the length and the breadth of the films in a systematic fashion. The as-deposited films are inhomogeneous from spot-to-spot over the surface. The variation in characteristic properties of 521 cm−1 line of crystalline Si (c-Si) have been used to estimate the thickness of the Al2O3 films. The thickness of the films has been found to depend on the position of the substrate with respect to the plume boundaries produced by the laser pulse after hitting the Al target. The thickness also depends on the position of the spot on a film placed at a fixed distance from the target surface. The thickness profiling of the deposited films on the basis of micro-Raman spectroscopic investigations corroborates the theoretical prediction of the model of the plume formation and the formation of the shock-front region in the pulsed laser deposition technique. All the seven Raman active modes (2A1g+5Eg) observable in single crystals of sapphire (c-Al2O3) powder have been identified in the complex spectra obtained from deposited film surfaces under varying experimental conditions. The intensity variation of an isolated line (750 cm−1) of Al2O3 corroborates the deposition profiling obtained from c-Si line parameters. The most intense Raman lines in the micro-Raman spectra of the deposited films are two infrared active modes around 450 and 600 cm−1. The strong presence of these infrared active modes in the micro-Raman spectra suggests a highly distorted micro-crystalline structure of the films. The local micro-stress created by the micro-crystals on the Si-substrate is maximum near the stopping distance of the plume. Largest micro-crystal of Al2O3 are also seen over the spot near the stopping distance of the plume.}, number={1}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Misra, A and Bist, HD and Navati, MS and Thareja, RK and Narayan, J}, year={2001}, month={Jan}, pages={49–54} }
 @article{kumar_narayan_nath_sharma_kvit_jin_2001, title={Tunable magnetic properties of metal ceramic composite thin films}, volume={119}, ISSN={["0038-1098"]}, DOI={10.1016/S0038-1098(01)00213-7}, abstractNote={We have developed a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline magnetic materials with accurate size and interface control. Using this method, single domain nanocrystalline Fe and Ni particles in 5–10 nm size range embedded in amorphous as well as crystalline alumina have been produced. Magnetization measurements of these layered thin films as function of field and temperature were carried out using a superconducting quantum interference device magnetometer. The size of Fe and Ni nanodots measured using transmission electron microscopy and calculated using magnetic data are in excellent agreement with each other.}, number={2}, journal={SOLID STATE COMMUNICATIONS}, author={Kumar, D and Narayan, J and Nath, TK and Sharma, AK and Kvit, A and Jin, C}, year={2001}, pages={63–66} }
 @article{wei_sankar_sharma_oktyabrsky_narayan_narayan_2000, title={Atomic structure, electrical properties, and infrared range optical properties of diamondlike carbon films containing foreign atoms prepared by pulsed laser deposition}, volume={15}, ISSN={["0884-2914"]}, DOI={10.1557/jmr.2000.0094}, abstractNote={We investigated the atomic structure, electrical, and infrared range optical properties of diamondlike carbon (DLC) films containing alloy atoms (Cu, Ti, or Si) prepared by pulsed laser deposition. Radial distribution function (RDF) analysis of these films showed that they are largely sp3 bonded. Both pure DLC and DLC + Cu films form a Schottky barrier with the measuring probe, whereas DLC + Ti films behave like a linear resistor. Pure DLC films and those containing Cu exhibit p-type conduction, and those containing Ti and Si have n-type conduction. Photon-induced conduction is observed for pure DLC, and the mechanism is discussed in terms of low-density gap states of highly tetrahedral DLC. Our results are consistent with relative absence of gap states in pure DLC, in accordance with theoretical prediction by Drabold et al.37 Temperature dependence of conductivity of DLC + Cu shows a behavior σ ∞ exp(−B/T1/2), instead of the T−1/4 law (Mott–Davis law). Contributions from band-to-band transitions, free carriers, and phonons to the emissivity spectrum are clearly identified in pure DLC films. The amorphous state introduces a large contribution from localized states. Incorporation of a small amount of Si in the DLC does not change the general feature of emissivity spectrum but enhances the contribution from the localized states. Cu and Ti both enhance the free carrier and the localized state contributions and make the films a black body.}, number={3}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Wei, Q and Sankar, J and Sharma, AK and Oktyabrsky, S and Narayan, J and Narayan, RJ}, year={2000}, month={Mar}, pages={633–641} }
 @article{yamagata_sharma_narayan_mayo_newman_ebihara_2000, title={Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part I. Optical emission spectroscopy}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1321783}, abstractNote={A comparative study of ablation plasma plumes originated from single crystal graphite (SCG) and amorphous carbon (a-C) targets during the preparation of diamond-like carbon (DLC) films by KrF excimer pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum, the emission lines of carbon neutral C and ions of C+, C2+, and C3+ can be observed from both the SCG and a-C plasma plumes. The emission intensity from C atoms increases with laser energy density (EL) increase for both cases. The C2 emission intensity from the SCG plasma plume changes drastically with EL, while that from the a-C plasma plume is almost constant. The C2/C emission intensity ratio for the a-C case decreases with EL increase. As for the SCG case, the C2/C ratio decreases with EL increase up to 3.0 J/cm2, and increases slightly with further EL increase. Nanohardness of the deposited films decreases with the increase of the C2/C emission intensity ratio. It is suggested that for both the SCG and a-C target cases, the C2 molecule in the ablated plasma plume may not play an important role in producing high quality DLC films. It is further proposed that the threshold of laser fluence for the formation of diamond-like character film using KrF excimer PLD is 2.1 J/cm2(0.84×108 W/cm2) for the a-C target and 3.0 J/cm2(1.2×108 W/cm2) for the SCG target. The C2 vibrational temperature of the SCG and the a-C plasma plumes show different features on both the laser energy density and nitrogen pressure dependencies. Through optical emission spectroscopy and Langmuir probe measurements in vacuum and nitrogen background, it is concluded that there are many particles with higher mass in the SCG plasma plume, especially at relatively lower laser energy density below 3.0 J/cm2.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yamagata, Y and Sharma, A and Narayan, J and Mayo, RM and Newman, JW and Ebihara, K}, year={2000}, month={Dec}, pages={6861–6867} }
 @article{mayo_newman_yamagata_sharma_narayan_2000, title={Comparative study of pulsed laser ablated plasma plumes from single crystal graphite and amorphous carbon targets. Part II. Electrostatic probe measurements}, volume={88}, ISSN={["0021-8979"]}, DOI={10.1063/1.1321784}, abstractNote={In an ongoing effort to investigate plasma plume features yielding high quality diamond-like carbon films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets. The advancing plasma plume produced by these structurally different targets are observed to possess quantitatively similar total heavy particle inventory, ionized fraction, and electron thermal content, yet quite different ion kinetic energy, plume profile, C2 formation mechanism, and concentration of complex molecules. Plume electron temperatures are observed to reside in the range 1–3 eV, with those in SCG plumes ∼10%–30% greater than a-C at all spatial positions downstream of the target. For both target cases, we find Te drop off with position away from the target with radiation as the most likely loss mechanism for these noninteracting plumes propagating in vacuum. Electron density is found to be ∼10%–12% lower near the target in SCG than a-C plumes consistent with mass loss inventory measurements, whereas ion fractions are estimated in the range ∼10%–15% for both target cases. All recorded data support the conclusion that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly comprised of C and C+ under vacuum conditions with the addition of C2 at high fill pressure. A significantly smaller profile peaking factor for SCG plumes supports this conclusion. Less energetic and slightly lower temperature SCG plume conditions are consistent with reduced peaking and more massive plume species. Plasma plumes from SCG targets exhibit laser energy (El) dependent peaking, again consistent with more complex molecules increasingly disassociated with El increase. The El dependence further suggests the potential for control of particle size distribution and plume profile peaking, though not independently. Consistent with this scenario is the observation of harder films produced from SCG targets at lower El. Micro-Raman results indicate strongly heterogeneous films deposited by SCG target ablation even under vacuum conditions further supporting the case for more complex structures with greater hardness. Energy balance estimates indicate that ion kinetic energy dominates the balance and that SCG ablation liberates about twice the number of C12 atoms from the target per unit El. As well, high pressure background fill indicates lesser plume energy attenuation for SCG plumes, again suggesting the presence of higher mass particles.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Mayo, RM and Newman, JW and Yamagata, Y and Sharma, A and Narayan, J}, year={2000}, month={Dec}, pages={6868–6874} }
 @article{mitsugi_yamagata_ikegami_ebihara_narayan_grishin_2000, title={Ferroelectric and colossal magnetoresistive properties of a PbZr1-xTixO3/La1-xSrxMnO3 heterostructure film}, volume={39}, ISSN={["0021-4922"]}, DOI={10.1143/JJAP.39.5418}, abstractNote={ 
  We report the ferroelectric and magnetoresistive properties and crystallization of a PbZr0.52Ti0.48O3 (PZT)/La0.8Sr0.2MnO3 (LSMO) heterostructure film prepared by pulsed-laser deposition on a MgO(100) single crystal substrate. Ferroelectric properties such as the hysteresis loop and dielectric constant of the Au/PZT/LSMO capacitor were compared with those of the Au/PZT/YBa2Cu3O7-x
                   (YBCO) superconductor heterostructure film. The resistivity of the LSMO film was as low as that of the YBCO film at room temperature. The fabricated Au/PZT/LSMO capacitor had a remanent polarization of 29 µC/cm2, a coercive field of 30 kV/cm and a dielectric constant of about 1000. 
  }, number={9B}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS}, author={Mitsugi, F and Yamagata, Y and Ikegami, T and Ebihara, K and Narayan, J and Grishin, AM}, year={2000}, month={Sep}, pages={5418–5420} }
 @misc{jain_willander_narayan_van overstraeten_2000, title={III-nitrides: Growth, characterization, and properties}, volume={87}, ISSN={["1089-7550"]}, DOI={10.1063/1.371971}, abstractNote={During the last few years the developments in the field of III–nitrides have been spectacular. High quality epitaxial layers can now be grown by MOVPE. Recently good quality epilayers have also been grown by MBE. Considerable work has been done on dislocations, strain, and critical thickness of GaN grown on different substrates. Splitting of valence band by crystal field and by spin-orbit interaction has been calculated and measured. The measured values agree with the calculated values. Effects of strain on the splitting of the valence band and on the optical properties have been studied in detail. Values of band offsets at the heterointerface between several pairs of different nitrides have been determined. Extensive work has been done on the optical and electrical properties. Near band-edge spectra have been measured over a wide range of temperatures. Free and bound exciton peaks have been resolved. Valence band structure has been determined using the PL spectra and compared with the theoretically calculated spectra. Strain and its effect on the optical properties of the III–nitride layers have been studied both theoretically and experimentally. Both n and p conductivity have been achieved. InGaN quantum wells with GaN and AlGaN barriers and cladding layers have been investigated. PL of the quantum wells is affected by confinement effects, band filling, quantum confined Stark effect, and strain. This work has led to the fabrication of advanced optoelectronic and electronic devices. The light-emitting decodes emitting in the blue and green regions of the spectrum have been commercialized. The work leading to these developments is reviewed in this article. The device processing methods and actual devices are not discussed.}, number={3}, journal={JOURNAL OF APPLIED PHYSICS}, author={Jain, SC and Willander, M and Narayan, J and Van Overstraeten, R}, year={2000}, month={Feb}, pages={965–1006} }
 @article{sharma_narayan_jin_kvit_chattopadhyay_lee_2000, title={Integration of Pb(Zr0.52Ti0.48)O-3 epilayers with Si by domain epitaxy}, volume={76}, ISSN={["1077-3118"]}, DOI={10.1063/1.126063}, abstractNote={High-quality lead zirconate titanate films (PZT) have been grown on yttrium barium copper oxide (YBCO) bottom electrode by domain epitaxy where integral multiples of lattice constants match across the interface. The YBCO films were epitaxially fabricated on Si (100) by introducing epilayer geometry of strontium titanate/magnesium oxide/titanium nitride. Pulsed-laser ablation was used to evaporate these five stoichiometric targets in a high vacuum chamber. X-ray diffraction and high-resolution transmission electron microscopy techniques were employed to gain understanding of the structure, crystallinity, and interfaces in these epilayers. The electrical characterization of the PZT films with evaporated silver contacts resulted in superior values of spontaneous polarization, remnant polarization, and coercive fields. This heterostructure opens a way for integration of epitaxial single-crystal PZT-based capacitors with silicon-based devices.}, number={11}, journal={APPLIED PHYSICS LETTERS}, author={Sharma, AK and Narayan, J and Jin, C and Kvit, A and Chattopadhyay, S and Lee, C}, year={2000}, month={Mar}, pages={1458–1460} }
 @article{aboelfotoh_borek_narayan_2000, title={Microstructure and electrical resistivity of Cu and Cu3Ge thin films on Si1-xGex alloy layers}, volume={87}, ISSN={["0021-8979"]}, DOI={10.1063/1.371868}, abstractNote={We have studied the reaction between Cu and ε1-Cu3Ge thin films and Si1−xGex (x=0.5) alloy layers epitaxially grown on Si(100) in the temperature range of 250–400 °C. In this temperature range, Cu reacts with the alloy to form a Cu3Si1−xGex ternary phase with an ordered body-centered-cubic crystal structure, and no Ge segregation occurs during the reaction. Unlike ε1-Cu3Ge, the Cu3Si1−xGex films exhibit a high-room-temperature resistivity of ∼150 μΩ cm. However, the Cu3Si1−xGex phase is not observed when Ge is added to Cu to form ε1-Cu3Ge. In contrast to the results reported for films of ε1-Cu3Ge formed on Si(100) substrates, the outdiffusion of Si into the ε1-Cu3Ge films is found to be suppressed when the films are formed on Si0.5Ge0.5 layers at temperatures up to 500 °C, and their resistivity remains low (typically less than 10 μΩ cm at room temperature), indicating the increased stability of ε1-Cu3Ge on Si1−xGex alloys. Furthermore, the ε1-Cu3Ge films form a sharp interface with the Si0.5Ge0.5 layers. These results indicate that ε1-Cu3Ge is an attractive candidate for contacts to SiGe-based devices.}, number={1}, journal={JOURNAL OF APPLIED PHYSICS}, author={Aboelfotoh, MO and Borek, MA and Narayan, J}, year={2000}, month={Jan}, pages={365–368} }
 @article{conrad_narayan_2000, title={On the grain size softening in nanocrystalline materials}, volume={42}, ISSN={["1359-6462"]}, DOI={10.1016/S1359-6462(00)00320-1}, abstractNote={In this study, Cu-Cr-Mg alloy wires were prepared by up-drawing continuous casting and multi-pass drawing. The effect of the solid solution process on the strength and electrical conductivity of the Cu-Cr-Mg alloy was investigated. The solid solution degree of Cu-Cr-Mg alloys with different solid solution processes was evaluated by XRD. The types and morphologies of nanoprecipitates of the two alloys during different thermomechanical treatments were compared by selected area electron diffraction in TEM, and the degree of recrystallization of the peak-aged Cu-Cr-Mg alloy was analyzed by EBSD. The results showed that the degree of supersaturated solid solution of the as-cast Cu-Cr-Mg alloy was comparable to that of the as-cast Cu-Cr-Mg alloy after holding at 950 ℃ for 1 h and water quenching. Meanwhile, the strength of the as-cast Cu-Cr-Mg alloy was 52.2 MPa higher than that of the solution-treated Cu-Cr-Mg alloy, and the decrease in conductivity was only 6.3% IACS. The microstructure results showed that a large number of dispersed nanoscale precipitates existed in the matrix of both alloys, and the precipitates were close in size. The results of the strengthened model calculations are also close to the experimental results.}, number={11}, journal={SCRIPTA MATERIALIA}, author={Conrad, H and Narayan, J}, year={2000}, month={May}, pages={1025–1030} }
 @misc{narayan_sharma_muth_2000, title={Optoelectronic and microelectronic devices including cubic ZnMgO and/or CdMgO alloys}, volume={6,423,983}, number={2000 Oct. 13}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J. and Sharma, A. K. and Muth, J. F.}, year={2000} }
 @article{teng_muth_kolbas_hassan_sharma_kvit_narayan_2000, title={Quantum confinement of E-1 and E-2 transitions in Ge quantum dots embedded in an Al2O3 or an AlN matrix}, volume={76}, ISSN={["0003-6951"]}, DOI={10.1063/1.125650}, abstractNote={Alternating layers of Ge quantum dots embedded in either Al2O3 or AlN matrices were deposited on sapphire substrates by pulsed-laser deposition. The characteristics of the dots are shown to be independent of the surrounding matrix. The dots size (73, 130, 160, and 260 ű5%) was controlled by the laser energy density and deposition time, and was characterized by high-resolution transmission electron microscopy. The dots were single crystalline with no apparent GeOx interfacial layers. Transmission spectroscopy at room temperature and 77 K was used to probe the above-band-edge absorption of the Ge nanodots. The spectral positions of both E1/E1+Δ1 and E2 transitions were found to shift to higher energy in the absorption spectra with decreasing nanodot sizes. This indicates that strong quantum-confinement effect permits the optical properties of Ge dots to be modified in a controlled manner.}, number={1}, journal={APPLIED PHYSICS LETTERS}, author={Teng, CW and Muth, JF and Kolbas, RM and Hassan, KM and Sharma, AK and Kvit, A and Narayan, J}, year={2000}, month={Jan}, pages={43–45} }
 @inproceedings{teng_muth_kolbas_hassan_sharma_narayan_2000, title={Quantum confinement of E1 and E2 transitions in Ge quantum dots embedded in Al203 or an AlN matrix}, booktitle={Optical microstructural characterization of semiconductors  (Materials Research Society proceedings, vol. 588)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Teng, C. W. and Muth, J. F. and Kolbas, R. M. and Hassan, K. M. and Sharma, A. K. and Narayan, J.}, editor={J. Piqueras, T. Sekiguchi and Unlu, M. S.Editors}, year={2000} }
 @article{teng_muth_ozgur_bergmann_everitt_sharma_jin_narayan_2000, title={Refractive indices and absorption coefficients of MgxZn1-xO alloys}, volume={76}, ISSN={["0003-6951"]}, DOI={10.1063/1.125912}, abstractNote={Indices of refraction for MgxZn1−xO epitaxial films grown by pulsed-laser deposition on sapphire substrates with x up to 0.36 were determined in the range of wavelength 457–968 nm by analysis of optical transmission spectra and prism-coupled waveguide measurements. The dispersion follows the first-order Sellmeier dispersion equation. Absorption coefficients, exciton energy gaps, and binding energies of MgxZn1−xO alloys were determined by transmission spectroscopy. The excitonic absorption features were clearly visible at room temperature despite alloy broadening. These results provide important information for the design and modeling of ZnO/MgZnO heterostructure optoelectronic devices.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Teng, CW and Muth, JF and Ozgur, U and Bergmann, MJ and Everitt, HO and Sharma, AK and Jin, C and Narayan, J}, year={2000}, month={Feb}, pages={979–981} }
 @inproceedings{hassan_sharma_narayan_muth_teng_kolbas_2000, title={Size effect in germanium nanostructures fabricated by pulsed laser deposition}, booktitle={Nanophase and Nanocomposite Materials III  (Materials Research Society proceedings; vol. 581)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Hassan, K. M. and Sharma, A. K. and Narayan, J. and Muth, J. F. and Teng, C. W. and Kolbas, R. M.}, editor={H. Hahn, S. Komarneni and Parker, J. C.Editors}, year={2000} }
 @inproceedings{sharma_jin_narayan_teng_muth_kolbas_holland_2000, title={Structural and optical property investigations on Mg-Alloying in epitaxial zinc oxide films on sapphire}, number={2000}, booktitle={MRS Internet Journal of Nitride Semiconductor Research}, author={Sharma, A. K. and Jin, C. and Narayan, J. and Teng, C. W. and Muth, J. F. and Kolbas, R. M. and Holland, O. W.}, year={2000} }
 @misc{wei_narayan_2000, title={Superhard diamondlike carbon: preparation, theory, and properties}, volume={45}, ISSN={["0950-6608"]}, DOI={10.1179/095066000101528340}, abstractNote={Abstract One of the many forms of carbon, diamondlike carbon (DLC) or tetrahedral amorphous carbon (ta-C) consists mainly of sp3 bonded carbon atoms. If properly prepared, DLC can have properties that rival those of crystalline diamond. The beneficial properties of DLC stem from the continuous rigid random networks of sp3 carbon atoms, and the properties can essentially be tailored by controlling the sp3/sp2 ratio. Techniques that have been successfully used to prepare high quality DLC coatings or thin films include pulsed laser ablation, filtered cathodic vacuum arc deposition, and mass selected ion beam deposition. Diamondlike carbon coatings that possess properties close to diamond in terms of hardness, atomic smoothness, infrared transparency, and chemical inertness can be processed easily with these techniques. In the past decade, tremendous progress has been made in experimental and theoretical investigations of hydrogen free DLC. Experimental and commercial applications in areas including microelectronics, microtribology, and biomedical technologies have been demonstrated. Potential applications include sensors, flat panel displays (field emitters), and photodiodes. Past and recent developments in synthesis and processing, properties, and modelling of hydrogen free superhard amorphous DLC are comprehensively reviewed. The techniques of fabrication, theoretical modelling, physical and mechanical characterisation, properties, and present and potential applications of DLC are discussed.}, number={4}, journal={INTERNATIONAL MATERIALS REVIEWS}, author={Wei, Q and Narayan, J}, year={2000}, pages={133–164} }
 @article{oktyabrsky_dovidenko_sharma_joshkin_narayan_1999, title={Crystal structure and defects in nitrogen-deficient GaN}, volume={4S1}, number={G6.43}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Oktyabrsky, S. and Dovidenko, K. and Sharma, A. K. and Joshkin, V. and Narayan, J.}, year={1999} }
 @article{oktyabrsky_dovidenko_sharma_narayan_joshkin_1999, title={Cubic GaN formation under nitrogen-deficient conditions}, volume={74}, ISSN={["0003-6951"]}, DOI={10.1063/1.123882}, abstractNote={We have studied crystal structure and associated defects in GaN/α-Al2O3 (0001) films grown under nitrogen-deficient conditions by metalorganic chemical vapor deposition and pulsed laser deposition. N-deficient films exhibit polycrystalline structure with a mixture of cubic zinc-blende and wurtzite hexagonal GaN grains retaining tetragonal bonding across the boundaries and hence the epitaxial orientations and polarity. Renucleation of the wurtzite phase at different {111} planes of cubic GaN results in a rough and faceted surface of the film. We elucidate that the cubic phase is more stable under the nitrogen deficiency.}, number={17}, journal={APPLIED PHYSICS LETTERS}, author={Oktyabrsky, S and Dovidenko, K and Sharma, AK and Narayan, J and Joshkin, V}, year={1999}, month={Apr}, pages={2465–2467} }
 @article{godbole_narayan_xu_narayan_sankar_1999, title={Diamond films and composites on cobalt-chromium alloys}, volume={58}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(98)00430-9}, abstractNote={Abstract Silicon, aluminum nitride (AlN) and titanium carbide (TiC) layers were deposited on cobalt–chromium alloys to investigate their utility as buffer layers for the synthesis of diamond films and composites. Silicon and aluminum nitride were found to react with the substrate at diamond deposition temperatures, via out-diffusion of cobalt from the substrate. The layers of titanium carbide, on the other hand, were found to be useful as a diffusion barrier for outward diffusion of cobalt and inward diffusion of carbon during diamond deposition, thus making enhanced nucleation and growth of high quality diamond possible. The continuous diamond coatings thus formed, however, tend to bulge and then crack due to thermal expansion mismatches between the TiC coated substrate and the overlayer diamond film. Composite coatings of AlN–diamond and TiC–diamond have, therefore, been synthesized by sequential deposition of component materials. These composite coatings consist of randomly interconnected micron sized diamond crystallites which are primarily surrounded by buffer material (AlN or TiC) while the contact area between neighbouring diamond crystallites is minimum. The presence of such a discontinuous morphology of diamond crystallites renders more toughness and also leads to compensation of stresses in localized regions (local stress management) and thus reduces bulging and subsequent delamination effects.}, number={3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Godbole, VP and Narayan, R and Xu, Z and Narayan, J and Sankar, J}, year={1999}, month={Mar}, pages={251–257} }
 @article{oktyabrsky_kalyanaraman_jagannadham_narayan_1999, title={Dislocation structure of low-angle grain boundaries in YBa2Cu3O7-delta/MgO films}, volume={14}, ISSN={["0884-2914"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032678410&partnerID=MN8TOARS}, DOI={10.1557/JMR.1999.0369}, abstractNote={Grain boundaries in laser-deposited YBa2Cu3O7−δ(YBCO)/MgO thin films have been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with thecaxis normal to the substrate surface and with misorientation in thea-bplane. The atomic structure of the grain boundaries was analyzed by using a dislocation model. Low-angle grain boundaries have been found to be aligned along (100) and (110) interface planes. For the (110) boundary plane, the low-energy dislocation configuration was found to consist of an array of alternating [100] and [010] dislocations. We have calculated the energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of the (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary. We have also modeled critical current transport through grain boundaries with various structures and found that the low-energy (110) grain boundary with dissociated dislocation array is expected to transport a lower superconducting current (by 25% for 6° misorientation) than (100) boundaries.}, number={7}, journal={JOURNAL OF MATERIALS RESEARCH}, author={Oktyabrsky, S and Kalyanaraman, R and Jagannadham, K and Narayan, J}, year={1999}, month={Jul}, pages={2764–2772} }
 @article{mayo_newman_sharma_yamagata_narayan_1999, title={Electrostatic measurement of plasma plume characteristics in pulsed laser evaporated carbon}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371135}, abstractNote={A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (∼3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0×1013–2.0×1014 cm−3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ∼10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions may play an important role in diamond-like carbon (DLC) film deposition. Electron temperature inferred from the electrostatic probe is found to consistently reside in the range 0.5–3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edge ion plume speed is measured via temporal displacement of spatially separated probe signals on consecutive PLE pulses. Flow speeds as high as 5.0×104 m/s are observed, corresponding to ∼156 eV in C+. The ion flow speed is found to be a strongly decreasing function of fill pressure from an average high of ∼126 eV in vacuum to ∼0.24 eV at 600 mTorr N2. Raman scattering spectroscopy indicates DLC film quality also degrades with fill pressure suggesting the importance of high ion kinetic energy in producing good quality films, consistent with earlier work demonstrating the importance of energetic particles. Optical emission indicates an increase in C2 molecular light intensity with fill gas pressure implying a reduced, if any, role of these species in DLC production. Ion current signal anomalies are often seen during high pressure pulses. It is suggested that this may indicate the formation of high mass carbon clusters during plume evolution in the presence of background gas. Mass diffusivity estimates, based on density decay, suggest the presence of C2+ under these conditions. Demonstration and control of such cluster formation may provide method(s) for controlling novel advanced materials properties.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Mayo, RM and Newman, JW and Sharma, A and Yamagata, Y and Narayan, J}, year={1999}, month={Sep}, pages={2865–2871} }
 @article{muth_kolbas_sharma_oktyabrsky_narayan_1999, title={Excitonic structure and absorption coefficient measurements of ZnO single crystal epitaxial films deposited by pulsed laser deposition}, volume={85}, ISSN={["1089-7550"]}, DOI={10.1063/1.370601}, abstractNote={The optical properties of high quality single crystal epitaxial zinc oxide thin films grown by pulsed laser deposition on c-plane sapphire substrates were studied. It was found that annealing the films in oxygen dramatically improved the optical and electrical properties. The absorption coefficient, band gap, and exciton binding energies were determined by transmission measurements and photoluminescence. In both the annealed and the as-deposited films excitonic absorption features were observed at both room temperature and 77 K. In the annealed films the excitonic absorption peaks were substantially sharper and deep level photoluminescence was suppressed.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Muth, JF and Kolbas, RM and Sharma, AK and Oktyabrsky, S and Narayan, J}, year={1999}, month={Jun}, pages={7884–7887} }
 @article{sharma_kvit_narayan_1999, title={Growth of single crystal MgO on TiN/Si heterostructure by pulsed laser deposition}, volume={17}, ISSN={["0734-2101"]}, DOI={10.1116/1.582071}, abstractNote={High quality epitaxial films of MgO have been grown on a Si (100) surface with TiN as a buffer layer by pulsed laser deposition. The electron diffraction patterns of these films confirmed the single crystal nature of the films with cube-on-cube epitaxy. It is difficult to grow high quality MgO films directly on Si due to large differences in lattice constants and thermal expansion coefficients of the two materials. The high resolution microscopy on our films revealed sharp interfaces between MgO/TiN and TiN/Si with no indication of interfacial reaction. Raman spectrum of MgO films revealed sharp peaks characteristic of MgO and TiN, indicating a good crystallinity. Further, superconducting YBa2Cu3O7−x films were grown on this heterostructure with a sharp transition at 88 K, indicating a high quality of the grown structure. This work opens a way for the growth of a variety of high quality perovskite structures for integration with silicon devices.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Sharma, AK and Kvit, A and Narayan, J}, year={1999}, pages={3393–3396} }
 @article{aboelfotoh_borek_narayan_1999, title={Interaction of Cu and Cu3Ge thin films with Si1-xGex alloys}, volume={75}, ISSN={["0003-6951"]}, DOI={10.1063/1.124804}, abstractNote={The interaction of Cu and Cu3Ge thin films with Si1−xGex (x=0.5) alloy layers epitaxially grown on Si(100) has been studied in the temperature range of 250–400 °C. In this temperature range, Cu reacts with the alloy to form a Cu3(Si1−xGex) ternary phase with an ordered body-centered-cubic crystal structure. The Cu3(Si1−xGex) phase exhibits high-room-temperature (∼150 μΩ cm) and nonmetallic resistivity. However, this ternary phase is not observed and the diffusion of Cu into the alloy is suppressed when Cu is replaced by low resistivity (typically less than 10 μΩ cm at room temperature) ε1-Cu3Ge phase. In contrast to the results reported for films of ε1-Cu3Ge formed on Si(100), the outdiffusion of Si into the ε1-Cu3Ge films is found to be suppressed when the films are formed on Si0.5Ge0.5 layers, indicating the increased stability of ε1-Cu3Ge on Si1−xGex alloys compared to pure silicon.}, number={12}, journal={APPLIED PHYSICS LETTERS}, author={Aboelfotoh, MO and Borek, MA and Narayan, J}, year={1999}, month={Sep}, pages={1739–1741} }
 @article{wei_sharma_sankar_narayan_1999, title={Mechanical properties of diamond-like carbon composite thin films prepared by pulsed laser deposition}, volume={30}, ISSN={["1879-1069"]}, DOI={10.1016/S1359-8368(99)00035-9}, abstractNote={We have investigated the mechanical properties of diamond-like carbon (DLC) thin films that contain foreign atoms. The DLC films were prepared by pulsed laser deposition. A novel target design was adopted to incorporate foreign atoms into the DLC films during film deposition. Copper, titanium and silicon are chosen as the dopants. The chemical composition of the doped films was determined using Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and calibrated extrapolation. Experimental results of both visible and UV Raman are presented and discussed in terms of peak shape and position. The effect of dopants on the Raman spectrum is also analyzed. Optical microscopy of the pure DLC of a certain thickness showed severe buckling. A brief review of the theoretical background of adhesion is given and the possible mechanisms of adhesion that may work in DLC coatings are discussed. Qualitative scratch tests on the specimens show that pure DLC has quite poor adhesion due to the large compressive stress, while the doped DLC films exhibit much improved adhesion. Wear tests show improved wear resistance in the doped DLC coatings. Nanoindentation results give an average hardness above 40 GPa and effective Young's modulus above 200 GPa for pure DLC. The copper doped DLC films showed slightly decreased hardness and Young's modulus as compared to pure DLC films. Ti and Si can reduce the hardness and Young's modulus more than Cu. All these can be understood by analyzing the internal stress reduction as derived from Raman G-peak shift to lower wavenumbers. A preliminary model of the stress reduction mechanism is discussed.}, number={7}, journal={COMPOSITES PART B-ENGINEERING}, author={Wei, Q and Sharma, AK and Sankar, J and Narayan, J}, year={1999}, pages={675–684} }
 @article{wei_sankar_kelkar_narayan_1999, title={Microstructure evolution accompanying high temperature; uniaxial tensile creep of self-reinforced silicon nitride ceramics}, volume={272}, ISSN={["0921-5093"]}, DOI={10.1016/s0921-5093(99)00497-9}, abstractNote={Extensive transmission electron microscopy (TEM) has been performed to study the microstructure evolution of a self-reinforced silicon nitride associated with high temperature creep. A large population of strain whorls is observed in samples crept at relatively high temperatures and the strain whorls are not necessarily asymmetrical with respect to the grain boundary normal. Large angle convergent beam electron diffraction (LACBED) at the grain boundaries where strain whorl contrast is visible reveals severely curved Bragg lines, implying large residual strains. This indicates that grain boundary interlocking might be effective to enhance the creep resistance at high temperatures. Dislocation pile-ups, arrays and tangles are present in certain silicon nitride grains. However, a simple analysis rules out dislocations as the major creep mechanism. Most dislocations started from grain boundaries. The role of dislocations is to relieve the stress concentrations at the strain whorls. This adds to the diffusion mechanism of stress relaxation at the strain whorls and facilitates other creep mechanisms such as grain boundary sliding. A large density of multiple-junction cavities is observed in the samples crept at relatively high temperatures. It is proposed that grain boundary sliding and cavity formation, in addition to stress relaxation through nucleation of dislocations at the strain whorls act together to produce a much shorter life to failure at high temperatures. While at lower temperatures, the creep is more diffusion controlled which gives a stress exponent of unity.}, number={2}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Wei, Q and Sankar, J and Kelkar, AD and Narayan, J}, year={1999}, month={Nov}, pages={380–388} }
 @article{aboelfotoh_borek_narayan_1999, title={Ohmic contact to p-type GaAs using Cu3Ge}, volume={75}, ISSN={["1077-3118"]}, DOI={10.1063/1.125505}, abstractNote={We have investigated ε1−Cu3Ge as an ohmic contact to p-type GaAs, and found that the ε1−Cu3Ge contact has a specific contact resistivity of 5×10−6 Ω cm2 on p-type GaAs with doping concentrations of ∼7×1018 cm−3. The ε1−Cu3Ge contact exhibits a planar and structurally abrupt interface with the GaAs, and no reaction between the contact metal and the GaAs is required for contact formation. The contact is electrically stable during annealing at temperatures up to 400 °C. It is suggested that Ge is incorporated into the GaAs as a p-type impurity resulting in a low contact resistivity. Furthermore, the addition of Ge to Cu to form ε1−Cu3Ge is found to impede the diffusion of Cu into the p-type GaAs. Along with the results reported for n-type GaAs, the present results indicate that ε1−Cu3Ge is an attractive candidate for ohmic contact formation on both n- and p-type GaAs.}, number={25}, journal={APPLIED PHYSICS LETTERS}, author={Aboelfotoh, MO and Borek, MA and Narayan, J}, year={1999}, month={Dec}, pages={3953–3955} }
 @article{sharma_narayan_muth_teng_jin_kvit_kolbas_holland_1999, title={Optical and structural properties of epitaxial MgxZn1-xO alloys}, volume={75}, ISSN={["1077-3118"]}, DOI={10.1063/1.125340}, abstractNote={The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices.}, number={21}, journal={APPLIED PHYSICS LETTERS}, author={Sharma, AK and Narayan, J and Muth, JF and Teng, CW and Jin, C and Kvit, A and Kolbas, RM and Holland, OW}, year={1999}, month={Nov}, pages={3327–3329} }
 @article{hassan_sharma_narayan_muth_teng_kolbas_1999, title={Optical and structural studies of Ge nanocrystals embedded in AlN matrix fabricated by pulsed laser deposition}, volume={75}, ISSN={["1077-3118"]}, DOI={10.1063/1.124648}, abstractNote={We have fabricated Ge nanostructures buried in a matrix of AlN grown on Si(111) by pulsed laser deposition at the substrate temperature of 500 °C. The characterization of these structures was performed using high-resolution transmission electron microscopy (HRTEM), photoluminescence, and Raman spectroscopy. The HRTEM results show that the Ge islands are single crystal with a pyramidal shape. The average size of Ge islands was determined to be ∼15 nm, which could be varied by controlling laser deposition and substrate parameters. The Raman spectrum showed a peak of the Ge–Ge vibrational mode downward shifted up to 295 cm−1 which is caused by quantum confinement of phonons in the Ge dots. The photoluminescence of the Ge dots (size ∼15 nm) was blueshifted by ∼0.266 eV from the bulk Ge value of 0.73 eV at 77 K, resulting in a distinct peak at ∼1.0 eV. The transmission measurements carried out on different samples having Ge dot sizes of 7, 8, and 13 nm deposited on sapphire substrate showed the above band edge transitions of Ge, which were also blueshifted in accordance with the quantum confinement effect. The importance of pulsed laser deposition in fabricating novel nanostructures is emphasized.}, number={9}, journal={APPLIED PHYSICS LETTERS}, author={Hassan, KM and Sharma, AK and Narayan, J and Muth, JF and Teng, CW and Kolbas, RM}, year={1999}, month={Aug}, pages={1222–1224} }
 @article{yamagata_sharma_narayan_mayo_newman_ebihara_1999, title={Optical emission study of ablation plasma plume in the preparation of diamond-like carbon films by KrF excimer laser}, volume={86}, ISSN={["0021-8979"]}, DOI={10.1063/1.371340}, abstractNote={Optical emission study of the laser ablation plasma plume during the preparation of diamond-like carbon (DLC) films using KrF excimer (248 nm) pulsed laser deposition (PLD) has been carried out by means of a monochromator equipped with an intensified optical multichannel analyzer. In high vacuum (1×10−7 Torr), the emission lines from carbon ions of C+, C2+, and C3+ are observed in addition to atomic carbon emission lines, while no emission from the diatomic carbon molecule (C2) is observed. With increasing background nitrogen pressure up to 500 mTorr, the emission intensities of the C2 Swan band and the carbon nitride (CN) violet band increase. The diamond-like character of deposited DLC film degrades with background nitrogen pressure. The vibrational temperature of C2 and CN molecules decreases with the increasing of nitrogen pressure. The CN vibrational temperature for the first 2 μs after the laser pulse is very high and in agreement with the kinetic energy of monatomic carbon ions. The C2 vibrational temperature is as low as 0.6 eV and is consistent with the electron temperature of about 0.8–3.0 eV. It is conjectured that CN molecules are formed directly in reactions involving energetic ionic monatomic carbon, and that the formation of excited C2 molecules is the result of molecular recombinations of C atoms and ions. From the emission intensity measurements and the estimation of the vibrational temperature, it is suggested that the C2 molecule in the ablated plasma plume is not important, but energetic species, such as C+, are very important for producing high quality DLC films using PLD.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yamagata, Y and Sharma, A and Narayan, J and Mayo, RM and Newman, JW and Ebihara, K}, year={1999}, month={Oct}, pages={4154–4159} }
 @article{wei_narayan_sharma_sankar_narayan_1999, title={Preparation and mechanical properties of composite diamond-like carbon thin films}, volume={17}, ISSN={["0734-2101"]}, DOI={10.1116/1.582074}, abstractNote={We have investigated mechanical properties of diamond-like carbon (DLC) thin films, particularly the internal compressive stress and ways to alleviate it. Foreign atoms such as copper, titanium, and silicon were incorporated into the DLC films during pulsed laser deposition. The chemical composition of the doped films was determined using Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy (XPS). Optical microscopy of the doped films showed that DLC films containing Cu exhibit much less particulate density as compared to the films containing Ti and Si. Visible Raman spectroscopy was used to characterize the films. The effect of dopants on the Raman spectrum was analyzed in terms of peak shape and position. Optical microscopy of the pure DLC of a certain thickness showed severe buckling. The mechanisms of adhesion associated with DLC coatings were discussed. Qualitative scratch tests on the specimens showed that pure DLC films have relatively poor adhesion due to a large compressive stress, while the doped DLC films exhibit much improved adhesion. Wear tests show improved wear resistance in the doped DLC coatings. Nanoindentation results suggest that pure DLC has an average hardness above 40 GPa and effective Young’s modulus above 200 GPa. The doped DLC films showed slightly decreased hardness and Young’s modulus as compared to pure DLC films. These results can be rationalized by analyzing the internal stress reduction as derived from Raman G-peak shift to lower wavenumbers. A preliminary interpretation of the stress reduction mechanism is discussed.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Wei, Q and Narayan, RJ and Sharma, AK and Sankar, J and Narayan, J}, year={1999}, pages={3406–3414} }
 @inproceedings{teng_muth_kolbas_hassan_sharma_kvit_narayan_1999, title={Quantum confinement of above-band-bap transitions in Ge quantum dots embedded in an Al2O3 or AIN matrix}, booktitle={Optical microstructural characterization of semiconductors  (Materials Research Society proceedings, vol. 588)}, publisher={Pittsburgh, Pa.: Materials Research Society}, author={Teng, C. W. and Muth, J. F. and Kolbas, R. M. and Hassan, K. M. and Sharma, A. K. and Kvit, A. and Narayan, J.}, editor={J. Piqueras, T. Sekiguchi and Unlu, M. S.Editors}, year={1999} }
 @article{dovidenko_oktyabrsky_narayan_razeghi_1999, title={Study of thin films polarity of group III nitrides}, volume={4S1}, number={G6.46}, journal={MRS Internet Journal of Nitride Semiconductor Research}, author={Dovidenko, K. and Oktyabrsky, S. and Narayan, J. and Razeghi, M.}, year={1999} }
 @article{kalyanaraman_oktyabrsky_narayan_1999, title={The role of Ag in the pulsed laser growth of YBCO thin films}, volume={85}, ISSN={["0021-8979"]}, DOI={10.1063/1.370172}, abstractNote={We have studied systematically the role of silver in improving microstructure and properties of Y1Ba2Cu3O7−δ (YBCO) thin films. We have more than doubled the grain size to nearly 1.8 μm and reduced processing temperatures by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approximately four times higher Jc than the best films obtained on MgO(001) substrates deposited from stoichiometric Y1Ba2Cu3O7−δ targets. Study of the silver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segregation of the Ag to the surface. The increased oxygen content in the films is also observed at lower processing temperatures, providing strong support for the efficient oxygenation of YBCO via the presence of silver. A qualitative model suggests that the formation of silver oxide, rapid surface diffusion of Ag on MgO surfaces, and the nonreactivity of Ag with YBCO are the key aspects to the improvement in microstructure. The possibility of extending these ideas to the growth of oxides is also discussed, along with the fabrication of in-situ superconducting-metal junctions with 3D geometries.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kalyanaraman, R and Oktyabrsky, S and Narayan, J}, year={1999}, month={May}, pages={6636–6641} }
 @article{godbole_dovidenko_sharma_narayan_1999, title={Thermal reactions and micro-structure of TiN-AlN layered nano-composites}, volume={68}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(99)00154-3}, abstractNote={Bilayer and multilayer structures of TiN and AlN thin films were synthesized using pulsed laser deposition technique in a substrate temperature range 300–700°C. The chemical reactions at TiN–AlN interfaces and the formation of different alloy phases were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was observed that TiN–AlN interface remains sharp and stable for deposition temperatures up to ∼650°C. At higher deposition temperatures, however, substantial chemical reactions were found to occur. The ternary alloy phases such as Ti3Al2N2 and Ti3AlN have been observed, for the first time. The composites synthesized at temperatures lower than 650°C and subsequently annealed at higher temperature were found to exhibit very limited or no interfacial chemical reactions. The effect of layer thickness on the microstructure is also studied. The studies revealed that by controlling the thickness of individual layers and substrate temperatures, it was possible to control microstructure and obtain composite coatings consisting of ternary Ti–Al–N alloy phases. The results are discussed in terms of characteristic features of pulsed laser ablation process in which evaporated flux contains energetic ions, electrons and neutral particles. Preliminary nano-indentation measurements and oxidation measurements reveal that these composites possess desirable mechanical properties at high temperatures.}, number={2}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Godbole, VP and Dovidenko, K and Sharma, AK and Narayan, J}, year={1999}, month={Dec}, pages={85–90} }
 @article{narayan_dovidenko_sharma_oktyabrsky_1998, title={Defects and interfaces in epitaxial ZnO/alpha-Al2O3 and AlN/ZnO/alpha-Al2O3, heterostructures}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368440}, abstractNote={We have investigated the nature of epitaxy, defects (dislocations, stacking faults, and inversion domains), and heterointerfaces in zinc oxide films grown on (0001) sapphire and explored the possibility of using it as a buffer layer for growing group III nitrides. High quality epitaxial ZnO films were grown on sapphire using pulsed laser deposition in the temperature range 750–800 °C. The epitaxial relationship of the film with respect to (0001) sapphire was found to be (0001)ZnO∥(0001)sap, with in-plane orientation relationship of [011̄0]ZnO∥[1̄21̄0]sap. This in-plane orientation relationship corresponds to a 30° rotation of ZnO basal planes with respect to the sapphire substrate, which is similar to the epitaxial growth characteristics of AlN and GaN on sapphire. The threading dislocations in ZnO were found to have mostly 1/3〈112̄0〉 Burgers vectors. The planar defects (mostly I1 stacking faults) were found to lie in the basal plane with density of about 105 cm−1. We have grown epitaxial AlN films at temperatures around 770 °C using ZnO/sapphire heterostructure as a substrate and observed the formation of a thin reacted layer at the AlN/ZnO interface. The implications of low defect content in ZnO films compared to III–V nitrides and the role of ZnO films as a buffer layer for III–V nitrides are discussed.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Narayan, J and Dovidenko, K and Sharma, AK and Oktyabrsky, S}, year={1998}, month={Sep}, pages={2597–2601} }
 @inproceedings{hassan_sharma_narayan_muth_teng_kolbas_1998, title={Germanium nanostructures fabricated by pulsed laser deposition}, booktitle={Microcrystalline and nanocrystalline semiconductors--1998: symposium held November 30-December 3, 1998, Boston, Massachusetts, U.S.A.}, author={Hassan, K. M. and Sharma, A. K. and Narayan, J. and Muth, J. F. and Teng, C. W. and Kolbas, R. M.}, year={1998} }
 @inproceedings{sharma_dovidenko_oktyabrsky_moxey_muth_kolbas_narayan_1998, title={Growth of high quality single crystal ZnO films on sapphire by pulsed laser ablation}, booktitle={Advances in laser ablation of materials: Symposium held April 13-16, 1998, San Francisco, California, U.S.A.  (Materials Research Society symposia proceedings ; v. 526).}, publisher={Warrendale, Pa.: Materials Research Society}, author={Sharma, A. K. and Dovidenko, K. and Oktyabrsky, S. and Moxey, D. E. and Muth, J. F. and Kolbas, R. M. and Narayan, J.}, year={1998}, pages={305} }
 @article{jagannadham_sharma_wei_kalyanraman_narayan_1998, title={Structural characteristics of AIN films deposited by pulsed laser deposition and reactive magnetron sputtering: A comparative study}, volume={16}, ISSN={["0734-2101"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032370406&partnerID=MN8TOARS}, DOI={10.1116/1.581425}, abstractNote={Aluminum nitride films have been deposited on Si(111) substrates at different substrate temperatures using two techniques; pulsed laser deposition or reactive magnetron sputtering. The films deposited by either of the techniques have been characterized by x-ray diffraction and transmission electron microscopy to determine the crystalline quality, grain size, and epitaxial growth relation with respect to the substrate. The bonding characteristics and the residual stresses present in the films have been evaluated using Raman and Fourier transform infrared spectroscopy. Secondary ion mass spectrometry has been performed to determine the nitrogen stoichiometry and the presence of impurities such as oxygen and silicon. The adhesion strength of the AlN films to the silicon substrate and the wear resistance have been determined by scratch test and a specially designed microscopic wear test. A comparison of the different characteristic features associated with the AlN films deposited by pulsed laser deposition or magnetron sputtering is presented with particular emphasis to electronic and tribological applications.}, number={5}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Jagannadham, K and Sharma, AK and Wei, Q and Kalyanraman, R and Narayan, J}, year={1998}, pages={2804–2815} }
 @article{fan_jagannadham_narayan_1997, title={Adhesion of diamond films on Ti-6Al-4V alloys}, volume={91}, ISSN={["0257-8972"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031131508&partnerID=MN8TOARS}, DOI={10.1016/S0257-8972(96)03107-6}, abstractNote={Diamond films have been successfully grown on Ti (Al 6%, V 4%) alloy by hot filament chemical vapor deposition (HFCVD). Different gas mixtures of methane to hydrogen and substrate temperatures were used in order to deposit high quality diamond films. Scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy, and microhardness measurements have been used to characterize the diamond films. The results indicate that uniform high quality diamond films can be grown on the titanium alloy at a partial pressure of 2660 Pa, ratio of methane to hydrogen of 0.5-1%, filament temperature 2273 K, and substrate temperature 1073 K. The hardness of the Ti alloy is increased 30% by coating with the diamond film. The adhesion measurements indicate that diamond films grown on the Ti alloy have excellent adhesion.}, number={1-2}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Fan, WD and Jagannadham, K and Narayan, J}, year={1997}, month={May}, pages={32–36} }
 @article{dovidenko_oktyabrsky_narayan_1997, title={Characteristics of stacking faults in AlN thin films}, volume={82}, ISSN={["0021-8979"]}, DOI={10.1063/1.366236}, abstractNote={We have investigated growth characteristics and atomic structure of defects in AlN thin films grown by the metalorganic chemical vapor deposition technique on the (101̄2) r plane of α-Al2O3. The AlN films were single crystal and exhibited the following epitaxial relationship: (112̄0)AlN∥(101̄2)sap with the in-plane alignment of [0001]AlN∥[1̄011]sap. Using high-resolution electron microscopy and multislice image simulation, the predominant defects in AlN thin films grown on the r plane of α-Al2O3 were found to be low-energy intrinsic stacking faults of type I1 lying in the basal plane. This fault, with a 1/6[202̄3] resultant displacement vector, can be formed by removing one (0002) plane and then shearing the remaining half-crystal by displacement of 1/3[101̄0]. The faults appear as a single face-centered-cubic stack ABC inserted into the normal …ABAB… hexagonal sequence. We discuss the possible role of these defects in optical properties of semiconductor devices.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Dovidenko, K and Oktyabrsky, S and Narayan, J}, year={1997}, month={Nov}, pages={4296–4299} }
 @article{jagannadham_fan_komanduri_narayan_1997, title={Comparison of microstructural features of diamond composite coatings with polycrystalline diamond or boron nitride brazed on tungsten carbide tools}, volume={15}, ISSN={["1520-8559"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031504189&partnerID=MN8TOARS}, DOI={10.1116/1.580733}, abstractNote={We have investigated microstructure and properties of diamond composite coatings on cemented tungsten carbide tool substrates, and compared wear resistance of these coatings with that of polycrystalline diamond (PCD) and polycrystalline boron nitride (PCBN) tools brazed on to cemented tungsten carbide substrates. The diamond composite coatings consist of layers of discontinuous diamond, TiC, and continuous diamond. In these composite layers, diamond is deposited by hot filament chemical vapor deposition and TiC by pulsed laser physical vapor deposition. Thermal stresses in the composite layer and the substrate are reduced and thereby help to improve the adhesion of diamond to the tool substrate. These tool coatings are characterized by scanning electron microscopy, Raman spectroscopy, secondary ion mass spectroscopy, and x-ray diffraction. The results of microstructural characterization and analysis of chemical composition are correlated with wear resistance. The present results demonstrate the advantages associated with composite diamond coatings compared to PCD and PCBN tool coatings.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Jagannadham, K and Fan, ND and Komanduri, R and Narayan, J}, year={1997}, pages={2262–2275} }
 @article{ding_choi_myers_sharma_narayan_cuomo_hren_1997, title={Field emission enhancement from Mo tip emitters coated with N containing amorphous diamond films}, volume={94}, number={1-3}, journal={Surface & Coatings Technology}, author={Ding, M. Q. and Choi, W. B. and Myers, A. F. and Sharma, A. K. and Narayan, J. and Cuomo, J. J. and Hren, J. J.}, year={1997}, pages={672–675} }
 @article{ding_myers_choi_vispute_camphausen_narayan_cuomo_hren_bruley_1997, title={Field emission from amorphous diamond coated Mo tip emitters by pulsed laser deposition}, volume={15}, number={4}, journal={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Ding, M. Q. and Myers, A. F. and Choi, W. B. and Vispute, R. D. and Camphausen, S. M. and Narayan, J. and Cuomo, J. J. and Hren, J. J. and Bruley, J.}, year={1997}, pages={840–844} }
 @article{kumar_kalyanaraman_vispute_narayan_christen_klabunde_1997, title={Giant magnetoresistance and non-ohmic effects in La0.6Y0.07Ca0.33MnOx thin films}, volume={45}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(96)01975-7}, abstractNote={Transport, magnetoresistance and structural properties of La0.6Y0.07Ca0.03MnOx(LYCMO) thin films grown in situ by pulsed laser ablation have been studied. Transmission electron microscopy and X-ray diffraction measurements have shown that the LYCMO films grow epitaxially on (100) LaAlO3 substrates and are cubic with a lattice parameter of 0.3849 run. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance at 125 K with a MR ratio (ΔR/RH) of 1500% in 6 Tesla magnetic field. By subsequent annealing of LYCMO films at 900 °C for half an hour in an oxygen ambient, this MR ratio was improved to 3200% at 192 K in the presence of the same magnetic field. This value of the MR ratio is the highest so far reported in this temperature regime. We ascribe this colossal magnetoresistance to the improved magnetic exchange between Mn3+ and Mn4+ ions resulting from the suppressed separation between Mn-O layers caused by a smaller sized Y-cation. We also report a non-ohmic response in the LYCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Kumar, D and Kalyanaraman, R and Vispute, RD and Narayan, J and Christen, DK and Klabunde, CE}, year={1997}, month={Mar}, pages={122–125} }
 @article{vispute_narayan_budai_1997, title={High quality optoelectronic grade epitaxial AlN films on alpha-Al2O3, Si and 6H-SiC by pulsed laser deposition}, volume={299}, ISSN={["0040-6090"]}, DOI={10.1016/S0040-6090(96)09395-9}, abstractNote={AlN is one of the most important optoelectronic materials in the wide band gap III–V semiconductors because of its wide and tunable energy band gap in conjunction with other nitrides, high thermal conductivity, doping capabilities, and high hardness. The proposed optoelectronic devices require high quality epitaxial films on various substrates. Here, we present our recent work on the fabrication of high quality epitaxial AlN films on Al2O3(0001), Si(111) and 6H-SiC(0001) by pulsed laser deposition (PLD). The PLD is a nonequilibrium technique where thin film growth temperature can be reduced by more than 250–350°C and epitaxial films comparable in quality to MOCVD (equilibrium technique) obtained. The laser fluence and the substrate temperature were found to be crucial processing parameters for the formation of high quality monocrystalline AlN films. The AlN films deposited above 750°C and laser energy densities of 2–3 J cm−2 were found to be epitaxial with c-axis normal to substrate plane. The X-ray rocking curve of epitaxial films on sapphire and SiC yielded full-width-at-half-maximum of ∼0.06–0.07°. The transmission electron microscopy also revealed that the films were epitaxial with an orientational relationship of AlN[0001]‖Al2O3[0001], AlN[0001]‖Si[111], AlN[0001]‖SiC[0001] and in-plane alignment of AlN[1̄21̄0]‖ Al2O3[01̄10], AlN[101̄0]‖Al2O3[2̄110], AlN[21̄1̄0]‖Si[011̄] and AlN[01̄10]‖SiC[01̄10]. The optical absorption edge measured by UV-visible spectroscopy for the epitaxial AlN film on sapphire was sharp and the band gap was found to be 6.1 eV. The electrical resistivity of the films was about 5–6×1013 Ω cm−1 with a breakdown field of 5×106 V cm−1.}, number={1-2}, journal={THIN SOLID FILMS}, author={Vispute, RD and Narayan, J and Budai, JD}, year={1997}, month={May}, pages={94–103} }
 @article{kalyanaraman_vispute_oktyabrsky_dovidenko_jagannadham_narayan_budai_parikh_suvkhanov_1997, title={Influence of oxygen background pressure on crystalline quality of SrTiO3 films grown on MgO by pulsed laser deposition}, volume={71}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.120011}, DOI={10.1063/1.120011}, abstractNote={We have systematically investigated the effect of oxygen partial pressure (PO2) on the crystalline quality of SrTiO3 films grown on MgO (001) substrates using pulsed laser deposition and established optimized conditions for the growth of high-quality epitaxial films. The crystalline quality is found to improve significantly in the O2 pressure range of 0.5–1 mTorr, compared to the films deposited at higher pressures of 10–100 mTorr. The x-ray diffraction rocking curves for the films grown at PO2 of 1 mTorr and 100 mTorr yielded full width at half-maximum (FWHM) of 0.7° and 1.4°, respectively. The in-plane x-ray φ scans showed epitaxial cube-on-cube alignment of the films. Channeling yields χmin were found to be <5% for the 1 mTorr films and ∼14% for 100 mTorr films. Thermal annealing of the SrTiO3 films in oxygen further improves the quality, and the 1 mTorr films give FWHM of 0.13° and χmin of 1.7%. In-plane misorientations of the annealed SrTiO3 films calculated using results of transmission electron microscopy are ±0.7° for 1 mTorr and ±1.7° for the 10 mTorr film. The high temperature superconducting (high-Tc) Y1Ba2Cu3O7−δ films grown on these SrTiO3/MgO substrates showed a χmin of 2.0% and transition temperature of ∼92 K, indicating that SrTiO3 buffer layers on MgO can be used for growth of high-quality Y1Ba2Cu3O7−δ thin film heterostructures for use in high-Tc devices and next generation microelectronics devices requiring films with high dielectric constants.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kalyanaraman, R. and Vispute, R. D. and Oktyabrsky, S. and Dovidenko, K. and Jagannadham, K. and Narayan, J. and Budai, J. D. and Parikh, N. and Suvkhanov, A.}, year={1997}, month={Sep}, pages={1709–1711} }
 @article{narayan_1997, title={Ion assisted laser processing of cubic boron nitride films}, volume={45}, ISSN={["0921-5107"]}, url={http://dx.doi.org/10.1016/s0921-5107(96)01970-8}, DOI={10.1016/s0921-5107(96)01970-8}, abstractNote={Abstract We have synthesized cubic boron nitride films using ion assisted laser deposition, where boron is evaporated by laser ablation and the substrate is bombarded concurrently with nitrogen ions. The films were characterized by Auger electron spectroscopy (AES), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) techniques. The electron diffraction patterns from these specimens provide unambiguous evidence for hexagonal (h-BN) and cubic (c-BN) boron nitride phases. The films deposited on silicon were found to be either polycrystalline h-BN or c-BN depending upon the deposition conditions. The films deposited on diamond were epitaxial cubic boron nitride with no interposing layer. We have performed a detailed study of microstructures of c-BN varying from fine-grain polycrystalline to epitaxial structures.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Narayan, J}, year={1997}, month={Mar}, pages={30–35} }
 @article{kumar_oktyabrsky_kalyanaraman_narayan_apte_pinto_manoharan_hegde_ogale_adhi_et al._1997, title={Role of silver doping in oxygen incorporation of oxide thin film}, volume={45}, ISSN={["0921-5107"]}, DOI={10.1016/s0921-5107(96)01920-4}, abstractNote={A distinctive characteristic of silver in oxygen incorporation of oxide thin films during pulsed laser ablation has been discovered. Optical emission spectroscopy studies of laser-induced plume of Ag-target indicates the presence of AgO species whose concentration increases with an increase in oxygen partial pressure. The formation of AgO in laser-plume has been found to be very useful for the realization of high temperature superconducting YBa2Cu3O7−δ (YBCO) and giant magnetoresistive La0.7MnO 3−δ (LMO) thin films with dramatically superior quality if the target materials contained a small amount of silver. The improvement in the quality of these films is brought about by the supply of atomic oxygen to oxide lattices during their formation. This becomes possible due to the fact that Ag, after it is ablated with other constituent materials in the target, gets moderately oxidized in an oxygen atmosphere and the oxidized species dissociate back into Ag and nascent O at the substrate surface. The nascent oxygen is very highly reactive and is easily assimilated into the lattice of these compounds.}, number={1-3}, journal={MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY}, author={Kumar, D. and Oktyabrsky, S. and Kalyanaraman, R. and Narayan, Jagdish and Apte, P. R. and Pinto, R. and Manoharan, S. S. and Hegde, M. S. and Ogale, S. B. and Adhi, K. P and et al.}, year={1997}, month={Mar}, pages={55–58} }
 @misc{sharma_narayan_1997, title={Synthesis and processing of superhard carbon nitride solids}, volume={42}, ISSN={["1743-2804"]}, DOI={10.1179/imr.1997.42.4.137}, abstractNote={Abstract Carbon nitride solids, predicted to exhibit bulk moduli comparable with or exceeding that of diamond, are reviewed for both theoretical and experimental developments. Progress in the theory and preparation of these solids is described detailing the structure, composition, thermodynamic aspects, and physical and mechanical properties. The synthesis and characterisation techniques involved are described from the viewpoint of their potential usefulness. Such issues as assessing the quality of synthesised films by revealing the nature of the chemical bonds between carbon and nitrogen and their chemical composition in each bonding state are discussed. Based on assessment of the experimental work to date, future directions for investigation of both amorphous and crystalline carbon nitrides are suggested. Some lattice matched compounds as suitable intermediate layers to promote the epitaxy of metastable C3N4 have been proposed and superlattice geometries with these lattice matched compounds are suggeste...}, number={4}, journal={INTERNATIONAL MATERIALS REVIEWS}, author={Sharma, AK and Narayan, J}, year={1997}, pages={137–154} }
 @article{dovidenko_oktyabrsky_narayan_razeghi_razeghi_1996, title={Aluminum nitride films on different orientations of sapphire and silicon}, volume={79}, number={5}, journal={Journal of Applied Physics}, author={Dovidenko, K. and Oktyabrsky, S. and Narayan, J. and Razeghi, M. and Razeghi, M.}, year={1996}, pages={2439–2445} }
 @article{vispute_wu_jagannadham_narayan_1995, title={Epitaxial growth of AlN thin films on silicon (111) substrates by pulsed laser deposition}, volume={77}, number={9}, journal={Journal of applied physics}, author={Vispute, R.D. and Wu, H. and Jagannadham, K. and Narayan, J.}, year={1995}, month={Jan}, pages={4724–4728} }
 @article{vispute_wu_narayan_1995, title={High quality epitaxial aluminum nitride layers on sapphire by pulsed laser deposition}, volume={67}, number={11}, journal={Applied Physics Letters}, author={Vispute, R.D. and Wu, Hong and Narayan, J.}, year={1995}, month={Nov}, pages={1549–1551} }
 @article{oktyabrsky_wu_vispute_narayan_1995, title={Misfit dislocations in low-temperature grown Ge/Si heterostructures}, volume={71}, ISSN={0141-8610 1460-6992}, url={http://dx.doi.org/10.1080/01418619508244467}, DOI={10.1080/01418619508244467}, abstractNote={Abstract We have investigated the initial stages of two-dimensional epitaxial growth of Ge on (001)Si substrates using pulsed laser deposition. The Ge films grow epitaxially above 170°C and switched from two- to three-dimensional growth mode above 350°C. The evolution of the dislocation network as a function of film thickness was studied by high-resolution transmission electron microscopy (TEM) in the films grown at 300°C and at relatively high growth rates to suppress the three-dimensional nucleation and obtain low rate of inelastic misfit relaxation. The relaxation process begins with generation of 60° slip dislocations with a strongly non-equilibrium inhomogeneous distribution which seems to be controlled by additional stress resulting from random surface undulations. When the film is just 8 nm thick, 90% of misfit stress is already relaxed by mostly 60° dislocations which demonstrate a distinct tendency of pairing of parallel dislocations from different glide planes. As the thickness of the film incre...}, number={3}, journal={Philosophical Magazine A}, publisher={Informa UK Limited}, author={Oktyabrsky, S. and Wu, H. and Vispute, R. D. and Narayan, J.}, year={1995}, month={Mar}, pages={537–551} }
 @misc{narayan_1995, title={Single crystal titanium nitride epitaxial on silicon}, volume={5,406,123}, number={1995 Apr. 11}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J.}, year={1995} }
 @article{zheleva_narayan_jagannadham_1994, title={Epitaxial growth in large‐lattice‐mismatch systems}, volume={75}, number={2}, journal={Journal of applied physics}, author={Zheleva, Tsvetanka and Narayan, J. and Jagannadham, K.}, year={1994}, month={Jan}, pages={860–871} }
 @article{narayan_biunno_kanetkar_tiwari_parikh_reddy_1994, title={Ion-assisted laser processing of CNx films}, volume={26}, number={1}, journal={Materials Science and Engineering: B}, author={Narayan, J. and Biunno, N. and Kanetkar, S.M. and Tiwari, P. and Parikh, N. and Reddy, J.}, year={1994}, month={Jan}, pages={49–53} }
 @misc{narayan_fan_1993, title={Dislocation density reduction in gallium arsenide on silicon heterostructures}, volume={5,208,182}, number={1993 May 4}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J. and Fan, J. C.}, year={1993} }
 @article{chen_narayan_1993, title={Effect of the chemical nature of transition‐metal substrates on chemical‐vapor deposition of diamond}, volume={74}, number={6}, journal={Journal of Applied Physics}, author={Chen, X. and Narayan, J.}, year={1993}, month={Sep}, pages={4168–4173} }
 @article{tiwari_singh_narayan_1993, title={Evaluation of physical and electrical properties of CoSi2 thin films on (100)Si grown by pulsed laser deposition}, volume={68}, ISSN={1364-2812 1463-6417}, url={http://dx.doi.org/10.1080/13642819308215296}, DOI={10.1080/13642819308215296}, abstractNote={Abstract Laser physical vapour deposition (LPVD) has been used to deposit thin CoSi2 films on (100) silicon at different substrate temperatures ranging from room temperature to 600°C. Silicide film...}, number={3}, journal={Philosophical Magazine B}, publisher={Informa UK Limited}, author={Tiwari, P. and Singh, R. and Narayan, J.}, year={1993}, month={Sep}, pages={413–420} }
 @misc{narayan_1993, title={Method for synthesis and processing of continuous monocrystalline diamond thin films}, volume={5,221,411}, number={1993 June 22}, publisher={Washington, DC: U.S. Patent and Trademark Office}, author={Narayan, J.}, year={1993} }
 @article{narayan_matera_singh_godbole_1992, title={Enhancement of nucleation and adhesion of diamond films on copper, stainless steel, and silicon substrates}, volume={71}, number={2}, journal={Journal of Applied Physics}, author={Narayan, J. and Matera, G. and Singh, R.K. and Godbole, V.P.}, year={1992}, month={Jan}, pages={966–971} }
 @article{narayan_tiwari_zheleva_chen_singh_chowdhury_1992, title={Epitaxial growth of TiN films on (100) silicon substrates by laser physical vapor deposition}, volume={61}, number={11}, journal={Applied Physics Letters}, author={Narayan, J. and Tiwari, P. and Zheleva, T. and Chen, X. and Singh, J. and Chowdhury, R.}, year={1992}, month={Sep}, pages={1290–1292} }
 @article{narayan_godbole_white_1991, title={Laser method for synthesis and processing of continuous diamond films on nondiamond substrates}, volume={252}, number={5004}, journal={Science}, author={Narayan, J. and Godbole, V.P. and White, C.W.}, year={1991}, month={Apr}, pages={416–418} }
 @article{singh_narayan_1990, title={PULSED-LASER EVAPORATION TECHNIQUE FOR DEPOSITION OF THIN-FILMS - PHYSICS AND THEORETICAL-MODEL}, volume={41}, ISSN={["0163-1829"]}, DOI={10.1103/physrevb.41.8843}, abstractNote={We have studied in detail the physical phenomena involved in the interaction of high-powered nanosecond excimer-laser pulses with bulk targets resulting in evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating these laser-plasma\char21{}solid interactions has been developed. In this model, the laser-generated plasma is treated as an ideal gas at high pressure and temperature, which is initially confined in small dimensions, and is suddenly allowed to expand in vacuum. The three-dimensional expansion of this plasma gives rise to the characteristic spatial thickness and compositional variations observed in laser-deposited thin films of multicomponent systems. The forward-directed nature of the laser evaporation process has been found to result from anisotropic expansion velocities of the atomic species which are controlled by the dimensions of the expanding plasma.}, number={13}, journal={PHYSICAL REVIEW B}, author={SINGH, RK and NARAYAN, J}, year={1990}, month={May}, pages={8843–8859} }
 @article{singh_narayan_bhattacharya_1990, title={Subsurface heating effects during pulsed laser evaporation of materials}, volume={57}, number={19}, journal={Applied Physics Letters}, author={Singh, Rajiv K. and Narayan, J. and Bhattacharya, D.}, year={1990}, month={May}, pages={2022–2024} }
 @article{singh_holland_narayan_1990, title={Theoretical model for deposition of superconducting thin films using pulsed laser evaporation technique}, volume={68}, number={1}, journal={Journal of Applied Physics}, author={Singh, Rajiv K. and Holland, O.W. and Narayan, J.}, year={1990}, month={Jan}, pages={233–247} }
 @article{singh_narayan_1989, title={A novel method for simulating laser-solid interactions in semiconductors and layered structures}, volume={3}, number={3}, journal={Materials Science and Engineering: B}, author={Singh, Rajiv K. and Narayan, Jagdish}, year={1989}, month={Jan}, pages={217–230} }
 @article{singh_narayan_singh_krishnaswamy_1989, title={In situ processing of epitaxial Y‐Ba‐Cu‐O high Tc superconducting films on (100) SrTiO3and (100) YS‐ZrO2 substrates at 500–650 °C}, volume={54}, number={22}, journal={Applied Physics Letters}, author={Singh, R.K. and Narayan, J. and Singh, A.K. and Krishnaswamy, J.}, year={1989}, month={May}, pages={2271–2273} }
 @article{krishnaswamy_narayan_vedam_mchargue_rengan_1989, title={Thin‐film deposition by a new laser ablation and plasma hybrid technique}, volume={54}, number={24}, journal={Applied Physics Letters}, author={Krishnaswamy, J. and Narayan, J. and Vedam, K. and McHargue, C.J. and Rengan, A.}, year={1989}, month={Dec}, pages={2455–2457} }
 @article{narayan_peters_yokota_ravi_srivatsa_1988, title={On epitaxial growth of diamond films on (100) silicon substrates}, volume={53}, number={19}, journal={Applied physics letters}, author={Narayan, J. and Peters, M. and Yokota, S. and Ravi, K.V. and Srivatsa, A.R.}, year={1988}, month={Jul}, pages={1823–1825} }
 @article{narayan_singh_holland_auciello_biunno_1987, title={Formation of thin superconducting films by the laser processing method}, volume={51}, number={22}, journal={Applied physics letters}, author={Narayan, J. and Singh, R. and Holland, O.W. and Auciello, O. and Biunno, N.}, year={1987}, month={Nov}, pages={1845–1847} }
 @article{mcmarr_vedam_narayan_1986, title={Spectroscopic ellipsometry: A new tool for nondestructive depth profiling and characterization of interfaces}, volume={59}, number={3}, journal={Journal of Applied Physics}, author={McMarr, P.J. and Vedam, K. and Narayan, J.}, year={1986}, month={Jan}, pages={694–701} }
 @article{vedam_mcmarr_narayan_1985, title={Nondestructive depth profiling by spectroscopic ellipsometry}, volume={47}, number={4}, journal={Applied Physics Letters}, author={Vedam, K. and McMarr, P.J. and Narayan, J.}, year={1985}, month={Aug}, pages={339–341} }
 @article{narayan_chen_moon_carpenter_1984, title={Characterization of metal precipitates in magnesium oxide}, volume={49}, ISSN={0141-8610 1460-6992}, url={http://dx.doi.org/10.1080/01418618408234929}, DOI={10.1080/01418618408234929}, abstractNote={Abstract A method, based on subtractive coloration or high-temperature reduction, has been developed to produce metal precipitates or colloids in oxides. The structure, symmetry, morphology and composition of precipitates were analysed by analytical electron microscopy and neutron scattering techniques. In the MgO: Ni system, the colloids were coherent nickel precipitates having a f.c.c. structure (ao = 3·52 A), and occasionally a b.c.c. structure (ao = 2·88A). The coherent precipitates were found to have either ⟨100⟩m‖⟨111⟩p or ⟨100⟩m‖⟨100⟩p matrix-precipitate relationship, depending on the high-temperature reduction treatment. From the neutron-magnetic-scattering measurements, the ratio of magnetic to nuclear scattering amplitudes for the (111) precipitate reflection was determined to be 17% below the value for pure nickel, indicating the presence of a magnetically ‘dead’ layer around the precipitates, a small amount of impurities incorporated into the precipitates, or a small fraction of another phase ...}, number={2}, journal={Philosophical Magazine A}, publisher={Informa UK Limited}, author={Narayan, J. and Chen, Y. and Moon, R. M. and Carpenter, R. W.}, year={1984}, month={Aug}, pages={287–300} }
 @article{holland_appleton_narayan_1983, title={Ion implantation damage and annealing in germanium}, volume={54}, number={5}, journal={Journal of Applied Physics}, author={Holland, O.W. and Appleton, B.R. and Narayan, J.}, year={1983}, month={May}, pages={2295–2301} }
 @article{narayan_holland_appleton_1983, title={Solid‐phase‐epitaxial growth and formation of metastable alloys in ion implanted silicon}, volume={1}, number={4}, journal={Journal of Vacuum Science & Technology B}, author={Narayan, J. and Holland, O.W. and Appleton, B.R.}, year={1983}, month={Oct}, pages={871–887} }
 @article{appleton_narayan_schow_williams_short_holland_lawson_1982, title={Characterization of damage in ion implanted Ge}, volume={41}, number={8}, journal={Applied Physics Letters}, author={Appleton, B.R. and Narayan, J. and Schow, O.E. and Williams, J.S. and Short, K.T. and Holland, O.W. and Lawson, E.}, year={1982}, month={Oct}, pages={711–712} }
 @article{narayan_1982, title={Interface structures during solid‐phase‐epitaxial growth in ion implanted semiconductors and a crystallization model}, volume={53}, number={12}, journal={Journal of Applied Physics}, author={Narayan, Jagdish}, year={1982}, month={Dec}, pages={8607–8614} }
 @article{white_pronko_wilson_appleton_narayan_young_1979, title={Effects of pulsed ruby‐laser annealing on As and Sb implanted silicon}, volume={50}, number={5}, journal={Journal of Applied Physics}, author={White, C.W. and Pronko, P.P. and Wilson, S.R. and Appleton, B.R. and Narayan, J. and Young, R.T.}, year={1979}, month={May}, pages={3261–3273} }
 @article{white_narayan_young_1979, title={Laser annealing of ion-implanted semiconductors}, volume={204}, number={4392}, journal={Science}, author={White, C.W. and Narayan, J. and Young, R.T.}, year={1979}, month={Apr}, pages={461–468} }
 @article{young_white_clark_narayan_christie_murakami_king_kramer_1978, title={Laser annealing of boron-implanted silicon}, volume={32}, number={3}, journal={Applied Physics Letters}, author={Young, R.T. and White, C.W. and Clark, G.J. and Narayan, J. and Christie, W.H. and Murakami, M. and King, P.W. and Kramer, S.D.}, year={1978}, month={Jan}, pages={139–141} }
 @article{narayan_young_wood_christie_1978, title={p‐n junction formation in boron‐deposited silicon by laser‐induced diffusion}, volume={33}, number={4}, journal={Applied Physics Letters}, author={Narayan, J. and Young, R.T. and Wood, R.F. and Christie, W.H.}, year={1978}, month={Aug}, pages={338–340} }
 @article{chen_narayan_abraham_tohver_1977, title={High-temperature and ionization-induced effects in lithium-doped MgO single crystals}, volume={16}, number={12}, journal={Physical Review B}, author={Chen, Y. and Narayan, J. and Abraham, M.M. and Tohver, H.T.}, year={1977}, month={Dec}, pages={5535} }