@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{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} }
 @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{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{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{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{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={Abstract}, 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{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{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{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{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{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={Abstract}, 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{gupta_sachan_bhaumik_narayan_2018, title={Enhanced mechanical properties of Q-carbon nanocomposites by nanosecond pulsed laser annealing}, volume={29}, ISSN={["1361-6528"]}, url={https://doi.org/10.1088/1361-6528/aadd75}, DOI={10.1088/1361-6528/aadd75}, abstractNote={Q-carbon is a metastable phase of carbon formed by melting and subsequently quenching amorphous carbon films by a nanosecond laser in a super undercooled state. As Q-carbon is a material harder than diamond, it makes an excellent reinforcing component inside the softer matrix of a composite coating. In this report, we present a single-step strategy to fabricate adherent coatings of hard and lubricating Q-carbon nanocomposites. These nanocomposites consist of densely-packed sp3-rich Q-carbon (82% sp3), and sp2-rich α-carbon (40% sp3) amorphous phases. The nanoindentation tests show that the Q-carbon nanocomposites exhibit a hardness of 67 GPa (Young’s modulus ∼ 840 GPa) in contrast to the soft α-carbon (hardness ∼ 18 GPa). The high hardness of Q-carbon nanocomposites results in 0.16 energy dispersion coefficient, in comparison with 0.74 for α-carbon. The soft α-carbon phase provides lubrication, resulting in low friction and wear coefficients of 0.09 and 1 × 10−6, respectively, against the diamond tip. The nanoscale dispersion of hard Q-carbon and soft α-carbon phases in the Q-carbon nanocomposites enhances the toughness of the coatings. We present detailed structure-property correlations to understand enhancement in the mechanical properties of Q-carbon nanocomposites. This work provides insights into the characteristics of Q-carbon nanocomposites and advances carbon-based superhard materials for longer lasting protective coatings and related applications.}, number={45}, journal={NANOTECHNOLOGY}, publisher={IOP Publishing}, author={Gupta, Siddharth and Sachan, Ritesh and Bhaumik, Anagh and Narayan, Jagdish}, year={2018}, month={Nov} }
 @article{narayan_bhaumik_sachan_2018, title={High temperature superconductivity in distinct phases of amorphous B-doped Q-carbon}, volume={123}, number={13}, journal={Journal of Applied Physics}, author={Narayan, J. and Bhaumik, A. and Sachan, R.}, year={2018} }
 @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{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{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{bhaumik_sachan_narayan_2017, title={A novel high-temperature carbon-based superconductor: B-doped Q-carbon}, volume={122}, number={4}, journal={Journal of Applied Physics}, author={Bhaumik, A. and Sachan, R. and Narayan, J.}, year={2017} }
 @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_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{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{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} }