@article{zhang_ronning_gofryk_mara_haberkorn_zou_wang_lee_bauer_mccleskey_et al._2012, title={Aligned carbon nanotubes sandwiched in epitaxial NbC film for enhanced superconductivity}, volume={4}, number={7}, journal={Nanoscale}, author={Zhang, Y. Y. and Ronning, F. and Gofryk, K. and Mara, N. A. and Haberkorn, N. and Zou, G. F. and Wang, H. Y. and Lee, J. H. and Bauer, E. and McCleskey, T. M. and et al.}, year={2012}, pages={2268–2271} }
 @article{zhang_zhu_rigsbee_suryanarayana_wang_liu_2007, title={Mechanical Behavior of nanostructured materials symposium honoring Carl Koch}, volume={59}, ISSN={["1047-4838"]}, DOI={10.1007/s11837-007-0116-2}, number={9}, journal={JOM}, author={Zhang, Xinghang and Zhu, Yuntian and Rigsbee, Mike and Suryanarayana, C. and Wang, Haiyan and Liu, C. T.}, year={2007}, month={Sep}, pages={49–49} }
 @article{matlock_zvanut_wang_dimaio_davis_van nostrand_henry_koleske_wickenden_2005, title={The effects of oxygen, nitrogen, and hydrogen annealing on Mg acceptors in GaN as monitored by electron paramagnetic resonance spectroscopy}, volume={34}, ISSN={["1543-186X"]}, DOI={10.1007/s11664-005-0177-3}, number={1}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Matlock, DM and Zvanut, ME and Wang, HY and Dimaio, JR and Davis, RF and Van Nostrand, JE and Henry, RL and Koleske, D and Wickenden, A}, year={2005}, month={Jan}, pages={34–39} }
 @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{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{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{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{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{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_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{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{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{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={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{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{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{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{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{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{zhang_wang_koch, title={Mechanical behavior of bulk ultrafine-grained and nanocrystalline Zn}, volume={6}, number={2}, journal={Reviews on Advanced Materials Science}, author={Zhang, X. and Wang, H. and Koch, C. C.}, pages={53–93} }