@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{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{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{zhou_chisholm_pant_chang_gazquez_pennycook_narayan_2010, title={Atomic structure of misfit dislocations in nonpolar ZnO/Al2O3 heterostructures}, volume={97}, number={12}, journal={Applied Physics Letters}, 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} }
 @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{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{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{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{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{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{narayan_pant_chugh_choi_fan_2006, title={Characteristics of nucleation layer and epitaxy in GaN/sapphire heterostructures}, volume={99}, number={5}, journal={Journal of Applied Physics}, author={Narayan, J. and Pant, P. and Chugh, A. and Choi, H. and Fan, J. C. C.}, year={2006} }