Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
7 results
Search Results
Item Structural, electrical and optical properties of stoichiometric In2Te3 thin films(Elsevier Ltd, 2017) Vallem, V.; Bangera, K.V.; Shivakumar, G.K.In2Te3 thin films were grown by thermal evaporation technique. The annealing of films played a major role to obtain stoichiometry, regardless of substrate temperature. Annealing at 300 ?C resulted in well oriented, mono-phased and nearly stoichiometric In2Te3 thin films. The variation in grain size of In2Te3 films associated with the substrate temperatures provides a significant control over the resistivity of the films, and the resistivity decreased with an increase in the grain size. The activation energy and optical band gap of stoichiometric In2Te3 films were found to be 0.01±0.005 eV and 0.99±0.02 eV, respectively. The absorption co-efficient of these films was found to be of the order of 105 cm?1. © 2016 Elsevier Ltd and Techna Group S.r.l.Item Optical properties of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber coatings by phase-modulated spectroscopic ellipsometry(Springer Verlag service@springer.de, 2017) Jyothi, J.; Biswas, A.; Sarkar, P.; Soum-Glaude, A.; Nagaraja, H.S.; Barshilia, H.C.TiAlC, TiAlCN, TiAlSiCN, TiAlSiCO, and TiAlSiO layers of thicknesses ~2.2 ?m, 755, 491, 393, and 431 nm, respectively, were deposited on stainless steel, silicon, and glass substrates to study their refractive indices and extinction coefficients using the phase-modulated spectroscopic ellipsometry in the wavelength range of 300–1200 nm. Absorption coefficient of each layer was calculated from the extinction coefficient of the layer. The results indicate that the first three layers (i.e., TiAlC, TiAlCN, and TiAlSiCN) are absorbing in nature, while TiAlSiCO and TiAlSiO act as intermediate and antireflection layers. Subsequently, a tandem absorber of TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO with layer thicknesses of 62, 20, 18, 16, and 27 nm, respectively, was deposited on stainless steel substrates to fabricate a spectrally selective coating with absorptance of 0.961 and emittance of 0.15 at 82 °C. The obtained refractive indices and extinction coefficients of the tandem absorber were used to simulate the reflectance of the deposited tandem absorber using SCOUT software. Simulated reflectance data of the tandem absorber showed a good agreement with the experimental data measured by UV–Vis–NIR and FTIR spectrophotometry. The angular dependence of the selective properties of the tandem absorber was studied by measuring the reflectance spectra of the tandem absorber at different incident angles. © 2017, Springer-Verlag GmbH Germany.Item Synthesis of single-phase stoichiometric InTe thin films for opto-electronic applications(Academic Press, 2019) Vallem, V.; Bangera, K.V.; G.k, S.Mono-phased and stoichiometric InTe thin films were successfully prepared using vacuum evaporation technique. A systematic variation in substrate temperature and annealing temperature along with annealing duration resulted stoichiometric and single phase InTe films. The annealing treatment of as-deposited films resulted in the structural transformation from mixed phase of In 2 Te 3 and InTe to mono-phased InTe. The electrical conductivity of stoichiometric single phase films was found to be 15.612 ? ?1 cm ?1 . The optical band gap of stoichiometric InTe films was found to be 1.42 eV and absorption coefficient of the films was of the order of 10 6 cm ?1 . Electrical properties of mono-phased films accompanied with optical properties such as direct band gap and absorption coefficient makes them suitable for optoelectronic devices. © 2019 Elsevier LtdItem Role of soaking time on the phase evolution of Cu2ZnSnS4 polycrystals synthesized using melting route for photovoltaic applications(Elsevier Ltd, 2019) Choudhari, N.J.; Raviprakash, Y.; Fernandes, B.J.; Udayashankar, N.K.Cu2ZnSnS4(CZTS) is an emerging quaternary semiconductor material to use as absorber layer for solar cells due its suitable band gap, high absorption coefficient, earth abundancy and less toxic nature. This work provides a comprehensive insight into the phase evolution of CZTS synthesized at a relatively lower process time. In this study, CZTS bulk polycrystals were synthesized using elemental pre cursors via melting route. The influence of soaking time on the structural, compositional and optical properties were investigated using XRD, EDS, Raman, DRS, PL and XPS measurements. XRD pattern revealed a highly crystalline tetragonal structure corresponding to kesterite phase. EDS mapping were performed over a large area of the sample revealed homogeneous distribution and near stoichiometric composition for the sample soaked for 14 h (S14). Raman spectra confirmed the existence of single phase CZTS without any secondary and ternary phases for S14. Diffuse reflectance spectroscopy gave a band gap value in the range 1.34–1.39 eV. PL analysis revealed that asymmetric band shape and higher energy shift is the characteristics of radiative transitions which are influenced by fluctuating potentials. XPS studies confirmed the oxidation states as Cu(I), Zn(II), Sn(IV) and S(II). © 2019 Elsevier B.V.Item Evaluation of photothermal properties for absorption of solar energy by Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans(Elsevier Ltd, 2020) Vijayanandan, A.S.; Kandath Valappil, R.S.; Mohan Balakrishnan, R.M.An attempt has been made to compare the optical properties of cobalt oxide (Co3O4) nanoparticles using experimental values and theoretical predictions. Optical transmittance of the nanoparticles obtained was higher than 65% in 550–850 nm containing visible spectrum and the experimental results were in accordance with the predictive datum. The absorption coefficient peak observed is close to the predictive value and is present in the visible region of the light. In addition, there was an excellent agreement between theoretical and experimental results in extinction coefficient and refractive index. Besides, this work proposes and validates a novel idea of using Co3O4 nanofluids to enhance solar thermal conversion efficiency. Co3O4 nanofluids synthesized using endophytic fungus Aspergillus nidulans isolated from a medicinal plant, Nothapodytes foetida has been used to illustrate the energy storage capacity of nanofluids. Experimental results reveal that Co3O4 nanofluids have good specific absorption rate (SAR) and better photo-thermal conversion efficiency than water. Nanofluid exhibited a greater temperature gradient than pure water, which is desired. Thus the good absorption ability of Co3O4 nanofluids for solar energy indicated that it is suitable for direct absorption solar thermal energy systems. © 2019Item Study on co-seismic energy losses from hypocenter to ocean bottom for Sumatra earthquake 2004 using 3-D crustal deformation model(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2020) Sonker, M.K.; Devi, R.; Singh, M.; Chand, R.Our co-seismic GRACE gravity data (Level 2 ‘RL_05’ data product “GX-OG-_2-GSM) for Sumatra earthquake 2004 is obtained by differencing monthly gravity field average for November 2004 from that of January 2005 and band-pass filtering (17–30, degrees and orders) in spectral domain. Here we propose an 11-layered 3-D thrust fault gravity model based on several co-seismic rupture models in literature. Previously we have covered the 3-D modelling details and its inferences like slip rate, seismic moment, momentum etc. in our published literature. Further we extend the inferences through our model for this case study. Here, we have estimated the layer-wise energy distribution by undertaking two types energy loss one is spherical spreading and second absorption with constrained by literature. We have computed layer-wise energy loss, equivalent energy, differential pressure, slip rate, ultimate slip and work done. The computed differential pressure and work done for Sumatra Earthquake 2004 are 1.7552 × 108 N/m2 and 1.657 × 1018 J, respectively. We also estimated the absorption coefficient (calculated absorption coefficients) from our model to honour the slip rate of Sumatra earthquake 2004. The differential pressure is estimated for ocean bottom and sea level surface. The volumetric analysis is also provided for entire 3-D body (layer-wise) using excess mass of our model. The computed differential pressure indeed corresponds to an area pulse at ocean bottom that led to a Tsunami generation. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.Item Synthesis, physicochemical properties and computational study of donor–acceptor polymer for optical limiting application(Springer Nature, 2020) Vishnumurthy, K.A.; Girish, K.H.; Vasudeva Adhikari, A.V.A new donor–acceptor configured ?-conjugated polymer P1 with alkoxy pendant groups having cyclic diimide and thiophene core moieties in polymer backbone were efficiently synthesized via polycondensation reaction. The incorporation of cyclic diimide in polymer increased the rigidity and thermal stability of polymer backbone aided by its high Tg value. These chromophores assisted in reducing the steric interaction of bulky alkoxy pendants which supported lowering the bandgap. The donor and acceptor moieties along with ? spacers were particularly chosen to enhance the ?-conjugation length in the polymer thereby increasing its nonlinear optical absorption i.e. two-photon absorption. The various structure–property relationships of the polymer were characterized by UV–Vis absorption, fluorescence emission, cyclic voltammetry, and density functional theory studies. The molecular nonlinear properties were theoretically evaluated through the calculation of polarizabilities and hyperpolarizabilities using time-dependent Hartree–Fock method. The polymer showed enhanced effective two-photon absorption with an absorption coefficient (?eff) of 2.031 × 10?10 m/W obtained from open aperture Z-scan analysis which is in good agreement with theoretical study. © 2020, Springer Nature Switzerland AG.