@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{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{bhosle_tiwari_narayan_2006, title={Electrical properties of transparent and conducting Ga doped ZnO}, volume={100}, number={3}, journal={Journal of Applied Physics}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, year={2006} }
 @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}, 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{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{bhosle_tiwari_narayan_2006, title={Metallic conductivity and metal-semiconductor transition in Ga-doped ZnO}, volume={88}, number={3}, journal={Applied Physics Letters}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, 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} }
 @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{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{bhosle_tiwari_narayan_2005, title={Epitaxial growth and properties of MoOx(2 < x < 2.75) films}, volume={97}, number={8}, journal={Journal of Applied Physics}, author={Bhosle, V. and Tiwari, A. and Narayan, J.}, year={2005} }
 @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{jin_tiwari_narayan_2005, title={Ultraviolet-illumination-enhanced photoluminescence effect in zinc oxide thin films}, volume={98}, ISSN={["1089-7550"]}, DOI={10.1063/1.2108156}, abstractNote={We report an enhancement effect of ultraviolet illumination on the photoluminescence intensities of zinc oxide thin films. Large-grain ⟨0001⟩-textured zinc oxide thin films were deposited on amorphous-fused silica substrates using pulsed laser deposition. We found that the intensities of excitonic emission and green-band emission increased with ultraviolet light exposure time until a maximum value was achieved. We attribute this ultraviolet radiation enhancement effect to oxygen desorption on the surface of the zinc oxide thin film. We have proposed a phenomenological model to explain this interesting photoluminescence behavior.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Jin, CM and Tiwari, A and Narayan, RJ}, year={2005}, month={Oct} }
 @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{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{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_2004, title={Special issue on nanostructured magnetic materials: Recent progress in magnetic nanostructures - Foreword}, volume={33}, ISSN={["0361-5235"]}, DOI={10.1007/s11664-004-0148-0}, number={11}, journal={JOURNAL OF ELECTRONIC MATERIALS}, author={Tiwari, A}, year={2004}, month={Nov}, pages={1253–1253} }
 @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{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{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{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{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{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{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{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{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{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{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} }