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    Characterization of silver selenide thin films grown on Cr-covered Si substrates
    (01-03-2009)
    Mohanty, Bhaskar Chandra
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    Malar, P.
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    Osipowicz, Thomas
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    Murty, B. S.
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    Varma, Shikha
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    Thermal stability of silver selenide thin films formed from the solid-state reaction of Ag-Se diffusion couples on Si substrates covered with a thin Cr film, is investigated. Glancing angle X-ray diffraction (GXRD), XPS, atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) are used to characterize the as-deposited films and those annealed at 100, 200, 300, and 400 °C. The results reveal the formation of polycrystalline orthorhombic silver selenide films that remain stable without compositional change upon thermal annealing, in marked contrast to the agglomeration exhibited by silver selenide films deposited on Si without Cr film. The improvement in the thermal stability is attributed to compressive stress relief by a grainy morphology with large surface area, the formation of which is promoted by partially oxidized Cr adhesion film. © 2008 John Wiley & Sons, Ltd.
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    SIMS study of effect of Cr adhesion layer on the thermal stability of silver selenide thin films on Si
    (01-04-2008)
    Mohanty, Bhaskar Chandra
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    Tyagi, A. K.
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    Balamurugan, A. K.
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    Varma, Shikha
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    Effect of heat treatment on silver selenide films grown from diffusion-reaction of Ag and Se films on Cr-buffered Si substrates was investigated up to 400 °C. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films. XRD patterns of the films showed stress assisted change in preferential orientation of the films upon annealing: the films annealed at 200 °C exhibited a strong orientation along (2 0 0) plane, which changed to (0 1 3) after annealing at 300 and 400 °C. Dynamic SIMS measurements showed that Cr is confined to the interface and that there is no diffusion of Cr into silver selenide. © 2007 Elsevier B.V. All rights reserved.
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    Growth and Rutherford backscattering spectrometry study of direct current sputtered indium oxide films
    (22-09-2005)
    Malar, P.
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    Mohanty, Bhaskar Chandra
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    In2O3 thin films were grown by direct current reactive sputtering. Structural investigations using X-ray diffraction and transmission electron microscopy confirmed the single-phase and polycrystalline nature of the films. Rutherford backscattering spectrometry study of the interface of In2O3 films with Si indicated the formation of ∼20 nm thick intermediate region consisting of silicon, oxygen and indium. Annealing at 875 K in oxygen atmosphere led to an increase in interface layer thickness. Broadening of the interface and diffusion of silicon into In2O3 were observed in films annealed in argon at 875 K. Oxygen-to-indium atomic concentration ratio in the as-grown films was ∼1.44, which was found to vary depending upon the annealing conditions. However, films deposited over Si/SiO2 showed a sharp interface between the In2O3 film and SiO2. © 2005 Elsevier B.V. All rights reserved.
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    Thermal stability of silver selenide thin films on silicon formed from the solid state reaction of Ag and Se films
    (05-12-2006)
    Mohanty, Bhaskar Chandra
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    Thermal stability of silver selenide thin films grown on silicon substrates by the solid state reaction of Se and Ag films is studied. The as-deposited as well as films annealed at different temperatures for 60 min in argon were investigated using X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM) measurements. Analysis of the XRD and RBS data of as-deposited films indicated the formation of single phase orthorhombic silver selenide from the reaction of Ag and Se films at room temperature. RBS spectra of films annealed at 473 K and above showed features characteristic of agglomerated morphology. SEM images showed the smooth morphology of the as-deposited films to evolve into a discontinuous island state with annealing temperature. The results suggest that above ∼ 473 K, the films are thermally unstable and agglomerate through holes generated at grain boundaries. © 2006 Elsevier B.V. All rights reserved.
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    Ion beam studies on reactive DC sputtered manganese doped indium tin oxide thin films
    (01-04-2008)
    Sarath Kumar, S. R.
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    Malar, P.
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    Osipowicz, Thomas
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    Banerjee, S. S.
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    Indium based transparent conducting oxides doped with magnetic elements have been studied intensively in recent years with a view to develop novel ferromagnetic semiconductors for spin-based electronics. In the present work, we have grown manganese doped indium tin oxide (Mn:ITO) thin films, onto Si and Si/SiO2 substrates by DC reactive sputtering of a composite target containing indium-tin alloy and manganese, in a gas mixture of oxygen and argon. Glancing angle X-ray diffraction (GXRD) studies reveal the polycrystalline nature of the films. Magnetic measurements carried out using vibrating sample magnetometer (VSM) suggest that the films are ferromagnetic at room temperature, with a saturation magnetization of ∼22.8 emu/cm3. The atomic percentages of In, Sn, Mn and O, as estimated using Rutherford backscattering spectrometry (RBS) are 37.0, 4.0, 1.6 and 57.4, respectively. RBS measurements reveal that the interface of the films with Si substrate has a ∼30 nm thick intermediate layer. This layer consists of oxygen, silicon, indium, tin and manganese, in the ratio 1:0.56:0.21:0.07:0.03, indicative of diffusion of elements across the interface. The films on Si/SiO2, on the other hand, have a sharp interface. © 2007 Elsevier B.V. All rights reserved.
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    Magnetic and electrical properties of Ho0.85Tb 0.15Fe2-xMnx (0, 0.5, 1.0, 1.5)
    (01-06-2004)
    Chelvane, J. Arout
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    The structural, magnetic and electrical properties of Ho 0.85Tb0.15Fe2Mnx (x = 0-0.15) have been characterized through X-ray diffraction, Curie temperature and electrical resistivity measurements. All the alloys are found to crystallize in C15-type cubic Laves phase structure. It is observed that the lattice parameter increases with increasing Mn concentration. The Curie temperature is found to decrease with increasing x, which is attributed to the net decrease in the exchange splitting of the spin-up and spin-down bands. All the materials are seen to exhibit metallic behavior with a decrease in the slope of ρ versus T curve near the Curie temperature. The resistivity behavior is explained on the basis of s-d scattering mechanism and electron-phonon interaction. Spin fluctuations have been observed through Curie temperature and resistivity measurements. © 2003 Elsevier B.V. All rights reserved.
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    Transparent ITO-Mn:ITO Thin-Film Thermocouples
    (01-01-2009)
    Kumar, S. R.Sarath
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    Transparent thin-film thermocouples have been fabricated with indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) as the positive and negative legs, respectively. Optical transparency of the thermocouples was above 85% in the visible region of the spectrum. Presence of Mn has been found to enhance the thermoelectric response, without significantly increasing the resistivity. Seebeck voltages of ~ 20 mV and ~ 31 mV have been obtained at 625 K, respectively, for the thermocouples with Mn:ITO legs having 1.6 at.% and 4.3 at.% Mn. The response has been found to be reproducible with an error of ±2%. © 2009, IEEE. All rights reserved.
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    Thermopower and optical studies on undoped and manganese doped indium tin oxide films
    (31-12-2009)
    Kumar, S. R.Sarath
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    Das, V. Damodara
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    Thermopower measurements in the range of 300-650 K along with room temperature optical absorption and electrical resistivity studies have been performed on indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) thin films grown by reactive DC sputtering. The thermopower of the films measured in Ar ambient displayed irreversible changes attributable to oxygen loss. Thermopower, carrier concentration and resistivity of the films have been found to depend on oxygen vacancies and Mn concentration. The observations have been substantiated with optical absorption and room temperature electrical resistivity results. It has also been observed that band gap tuning in these films is possible by the introduction of Mn as well as oxygen vacancies. © 2009 Elsevier B.V. All rights reserved.
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    A hot probe setup for the measurement of Seebeck coefficient of thin wires and thin films using integral method
    (07-03-2008)
    Kumar, S. R.Sarath
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    An experimental setup is developed for the measurement of the Seebeck coefficient of thin wires and thin films in the temperature range of 300-650 K. The setup makes use of the integral method for measuring the Seebeck voltage across the sample. Two pointed copper rods with in-built thermocouples serve as hot and cold probes as well as leads for measuring the Seebeck voltage. The setup employs localized heating and enables easy sample loading using a spring loaded mounting system and is fully automated. Test measurements are made on a constantan wire and indium tin oxide (ITO) thin film for illustration. The Seebeck voltage obtained for constantan wire is in agreement with the NIST data for copper constantan couple with an error of 1%. The calculated carrier concentration of ITO film from the Seebeck coefficient measurement is comparable with that obtained by electrical transport measurements. The error in the Seebeck coefficient is estimated to be within 3%. © 2008 American Institute of Physics.
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    Micro-raman spectroscopy studies of bulk and thin films of cuInTe 2
    (24-08-2009)
    Ananthan, M. R.
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    Mohanty, Bhaskar Chandra
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    Micro-Raman spectroscopy measurements were made on polycrystalline and amorphous thin films of CuInTe2 as well as bulk polycrystalline CuInTe2. Various vibrational modes exhibited by the bulk and polycrystalline thin films were attributed to those expected for single crystal CuInTe2. Raman spectra of amorphous films presented a broad spectrum, decomposition of which revealed the presence of elemental tellurium on the film surface. Laser-induced changes on CuInTe2 thin films were studied by acquiring spectra with higher laser beam power. Modes due to tellurium appeared when the spectra were acquired during laser-sample interaction, indicating tellurium segregation. The Raman spectra measured from polycrystalline films during high laser power irradiation did not show decrease in the intensity of the A1 mode of CuInTe2 in spite of loss of tellurium from the lattice. This has been interpreted as related to an increased contribution from the undistorted subsurface CuInTe2 region at higher excitation power. © 2009 IOP Publishing Ltd.