Faculty Publications
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Item Growth and morphology of mixed K1-x(NH4)xH2PO4 crystals(Elsevier Ltd, 2010) Shenoy, P.; Bangera, K.V.; Shivakumar, G.K.Mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP), i.e., potassium ammonium dihydrogen phosphate, K1-x(NH4)xH2PO4 have been grown by slow evaporation from the supersaturated solution at an ambient temperature 26 ± 1 °C for ammonium concentration x in the range 0.0 ? x ? 1.0. The morphology changes from tetragonal prism to needles when the concentration of either of the components approaches that of the other. Induction periods were measured for various compositions of mixed crystals of ADP and KDP by the direct vision method. Crystal compositions were determined by flame atomic absorption spectroscopy and also by chemical analysis. Results of the X-ray analysis of the grown crystals are also reported. Maximum size of the grown mixed crystal was around 16 × 10 × 4 mm3. © 2010 Elsevier B.V. All rights reserved.Item Effect of indium content on the characteristics of indium tin oxide thin films(Institute of Physics Publishing helen.craven@iop.org, 2018) Navya, K.; Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.Transparent IxT1-xO (x = 0 to 1) alloyed thin films were deposited by spray pyrolysis technique at a substrate temperature of 400 °C. The effect of incorporation of indium on structural, optical and electrical properties of tin oxide thin films were studied. Characterization of thin films was carried out using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDAX), UV-Visible absorption spectroscopy. XRD results revealed that IxT1-xO thin films were polycrystalline in nature with good crystallinity. Incorporation of indium effectively modifies the surface morphology of the films. The band gap was varied from 3.7 eV to 3 eV. Maximum electrical conductivity of 44.52 × 103 ?-1 m-1 and transmittance of 90% is obtained for I0.5T0.5O films, hence can be used as highly transparent and conducting electrodes. © 2018 IOP Publishing Ltd.Item A comprehensive study on the structural, morphological, compositional and optical properties of ZnxCd1-xS thin films(Institute of Physics Publishing helen.craven@iop.org, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.The absorption loss in cadmium sulfide (CdS) thin films which are widely used as a window layer in a photovoltaic cell limits the efficiency of the device. This issue can be addressed by ZnxCd1-xS thin films due to its tunable band gap nature. Herein, the various composition of ZnxCd1-xS (x=0, 0.15, 0.30, 0.45, 0.70, 0.85, 1) thin films were grown by a vacuum thermal evaporation technique and the characteristics of the films were investigated by varying the composition 'x'. The x-ray diffraction (XRD) studies displayed that the as-deposited films consist of diffraction peaks from both CdS and ZnS lattice. The formation of ternary ZnxCd1-xS films was verified when the deposited films were subjected to an annealing treatment. The morphology of the films was analyzed using a scanning electron microscope (SEM) and it was observed that the films are uniform, homogeneous and free from any pin-holes and cracks. The presence of Zn, Cd and S elements were quantized using an energy dispersive spectroscopy. Optical studies showed a successful non-linear band gap engineering (2.42-3.49 eV) for the deposited ZnxCd1-xS thin films. All films showed a very high optical transmittance of above 70% in the visible wavelength region. © 2020 IOP Publishing Ltd.Item Investigation of third-order nonlinear optical properties of nanostructured Ni-doped CdS thin films under continuous wave laser illumination(Springer, 2019) Bairy, R.; Arasalike, A.; Shivakumar, G.K.; Radhakrishnan, K.; Bhat K, U.K.We report the third-order nonlinear optical (NLO) properties and optical limiting (OL) thresholds of pure CdS and Ni-doped CdS thin films have been investigated with the Z-scan technique under continuous wave laser excitation. Nanocrystalline CdS thin films with various doping concentrations of Ni (0%, 1%, 3%, 5% and 10 at. %) are prepared by spray-pyrolysis technique. XRD patterns reveal that all the prepared films are polycrystalline and the incorporation of Ni does not lead to major changes in the crystalline phase of Cd1-xNixS thin films. The surface morphology of the prepared films is impacted by the Ni-doping and is indicated by Field Emission Scanning Electron Microscopy (FESEM) images. With an increase in Ni-doping concentration, the energy band-gap value decreased from 2.48 eV to 2.23 eV. From the Z-scan data, it is observed that the material show strong two-photon absorption (2PA) and with an increase in Ni-doping concentrations from 0 to 10 at. %, the nonlinear absorption coefficient (?) are enhanced from 0.92 x 10-5 to 4.46 x 10-5 (cm W-1), nonlinear refractive index (n2) from 0.2967 x 10-9 to 0.1297 x 10-8 (cm2 W-1) and thereby the third-order NLO susceptibility (?(3)) values also increased from 1.7075 x 10-6 to 7.4743 x 10-6 (esu). OL characteristics of the prepared films are studied at the experimental wavelength. The results propose that the Cd1-xNixS film is a capable material for nonlinear optical devices at 532 nm and optical power limiting applications. © Springer Science+Business Media, LLC, part of Springer Nature 2019.Item Synthesis and characterization of Cu 1-x Zn x O composite thin films for sensor application(Elsevier Ltd, 2019) Bharath, S.P.; Bangera, K.V.; Shivakumar, G.K.Cu 1-x Zn x O composite thin films were prepared using industrially applicable spray pyrolysis technique for volatile organic compound (VOCs)sensor application. Sensing properties for different concentration of VOCs such as acetone, ethanol and methanol were studied at different sensor operating temperature. XRD studies on prepared thin films confirmed formation of CuO[sbnd]ZnO composite thin films with presence of different peaks for monoclinic structured CuO and hexagonal structure ZnO, it was also observed that formation of composite material improves sensing property towards VOCs. Granular morphology observed from SEM images were also contributed to enhance sensitivity of Cu 1-x Zn x O thin films. Hot probe experiment reveals that all the thin films were p-type in conductivity nature. Maximum electrical conductivity was achieved for Cu 0.75 Zn 0.25 O composite thin films, which also showed highest sensing property for VOCs. Cu 0.75 Zn 0.25 O thin films were selective towards ethanol and were capable of detecting 1 ppm of ethanol at operating temperature of 290 °C. © 2019Item Evaluation of semiconducting p-type tin sulfide thin films for photodetector applications(Academic Press, 2019) Barman, B.; Bangera, K.V.; Shivakumar, G.K.Tin sulfide (SnS) is an important semiconductor as it is one of the less common p-type materials with a bandgap of 1.53 eV which makes it an attractive material for photo detector application. In the thin film form, it is a sensitive photo conductor with attractive opto-electronic characteristics. In the current report, tin sulfide thin films have been deposited by thermal evaporation in vacuum and the influence of substrate temperature on its compositional, morphological, structural, and opto-electrical properties was studied. X-ray diffraction (XRD) study shows that all the thermally deposited films are having an orthorhombic crystal structure along (111) plane as pre-dominant orientation and are polycrystalline in nature. Raman analysis verify the occurrence of SnS and Sn2S3 phases in the films. Surface morphology along with the elemental composition of the films was determined by scanning electron microscopy (SEM) in combination with energy dispersive spectroscopy (EDS). All the films were found to be homogeneous, uniform, pin-hole free and have high optical transmittance in the UV–Vis wavelength region. The optical bandgap energy of the films was calculated using Tauc's relation and it was found to be decreasing (1.576 eV–1.429 eV) with increasing substrate temperature. The activation energy of the SnS thin films was calculated from Arrhenius plot and it was also found to be decreasing with increasing substrate temperature. The opto-electrical parameters such as photo conductivity (?L), dark conductivity (?D), response time (?r), recovery time (?d), photoresponsivity (R), and photosensitivity (S) were calculated and was found best for the films grown at 323 K. © 2019 Elsevier Ltd