@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{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} }
 @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}, number={14}, journal={Applied Physics Letters}, author={Tiwari, A. and Bhosle, V. M. and Ramachandran, S. and Sudhakar, N. and Narayan, J. and Budak, S. and Gupta, A.}, year={2006} }
 @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} }
 @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{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} }