Faculty Publications
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Item The p-type doping of vacuum deposited ZnTe thin films with bismuth by a new technique of using nano-spheres(Elsevier Ltd, 2010) Rao, K.G.; Shivakumar, G.K.; Kasturi, V.B.The present paper reports the successful doping of vacuum evaporated zinc telluride (ZnTe) thin films with bismuth by a new technique of using nano-spheres. The discontinuous films of bismuth (the dopant material), containing bismuth in the form of nano-spheres, were prepared by vacuum evaporation and the ZnTe films were then deposited on top of them. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to ascertain the formation of discontinuous bismuth films and the proper diffusion of bismuth in ZnTe films, respectively. After doping, the carrier concentration of the ZnTe films was found to increase by an order of the magnitude. The electrical conductivity also improved significantly. The photoconductivity and photo-response properties of the doped films were also analysed. © 2010 Elsevier B.V. All rights reserved.Item Electrical switching in Si20Te80 ? xBix (0 ? x ? 3) chalcogenide glassy alloys(Elsevier B.V., 2018) Fernandes, B.J.; Ramesh, K.; Udayashankar, N.K.Chalcogenide glasses have attained enormous research interest due to their importance in finding electronic memories. Here we report electrical switching and thermal crystallization behavior of Si20Te80 ? xBix (0 ? x ? 3) glasses. We observe a significant decrease in the threshold voltage (VT) and the thermal stability (?T), indicating that in Si20Te80 ? xBix glasses, the resistivity of the additive element Bi plays a dominant role over network connectivity/rigidity. The variation of VT with respect to thickness and temperature of the sample indicates that the memory switching observed in Si20Te80 ? xBix glasses is influenced by the thermally induced transitions (thermal mechanism). Scanning electron microscopy (SEM) studies on pre-switched and post switched samples reveal the morphological changes on the surface of the sample, and serve as an experimental evidence for the formation of the crystalline filament between two electrodes during switching. Furthermore, the decrease in ?T values indicates that the Si-Te glasses become de-vitrifiable more easily with the addition of Bi, influencing the decrease of VT. Structural evaluation like thermal devitrification studies and morphological changes elucidate the restricted glass formability of the studied glass system. © 2018 Elsevier B.V.Item A compact and efficient graphene FET based RF energy harvester for green communication(Elsevier GmbH, 2020) Singh, N.; Kumar, S.; Kumar Kanaujia, B.K.; Beg, M.T.; Mainuddin, M.; Kumar, S.This paper presents a graphene field effect transistor (FET) based rectenna with substrate-integrated waveguide (SIW) broadband approach for RF energy harvesting application. The proposed structure of integrated rectenna consists of a graphene FET rectifier and an SIW antenna operating in the (S11 < ?10 dB) range of 29–46 GHz. The peak gain of the SIW antenna observed is 8.12 dBi. In addition, a new matched circuit consisting of microstrip line and butterfly stub (without using any lumped elements) is designed. The matched circuit provides a miniaturized block by reducing the size and eliminating parasitic reactance in the integrated rectenna. The proposed rectenna is implemented and fabricated using two superimposed layers: RT/duroid 5880 and graphene substrate with a compatible approach. A measured conversion efficiency of 80.32% is obtained. The dimensions of the proposed antenna and rectifier are 3.2 × 3.2 × 0.4 mm3 and 3.2 × 10 × 0.4 mm3, respectively. The proposed rectenna covers Ka- and Q-band applications and could be a potential candidate for contemporary energy harvesting systems. © 2019 Elsevier GmbHItem Bismuth oxybromide nanoplates embedded on activated charcoal as effective visible light driven photocatalyst(Elsevier B.V., 2020) Shenoy, S.; Sridharan, K.Nanostructured bismuth oxybromide (BiOBr) are one among the most significantly researched visible light driven photocatalyst, but their low specific surface area hinders higher rate of photodegradation. Herein, a single-step solution based synthesis technique is adopted to embed BiOBr on very little quantities of activated charcoal (AC), thereby improving its specific surface area and visible light absorption range. Nanoplate morphology of BiOBr and their embedment on AC are confirmed from electron microscopy. Interestingly, the embedment of BiOBr on just 0.5 wt% of AC (BiOBr-AC0.5) significantly enhanced the rate of salicylic acid photodegradation, which was six-fold higher than that of pristine BiOBr. © 2020 Elsevier B.V.Item Complementary effect of co-doping aliovalent elements Bi and Sb in self-compensated SnTe-based thermoelectric materials(Royal Society of Chemistry, 2021) Kihoi, S.K.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.Research on Pb-free thermoelectric materials as a potential eco-friendly and solid-state source of energy has continuously advanced over time, with SnTe-based materials having shown utmost promising properties owing to their tunable electronic structure and scalable thermal conductivity. In this study, we self-compensate Sn to reduce inherent Sn vacancies, and further tune the carrier concentration by doping with Bi. Sb is further alloyed to incorporate nanostructures that significantly reduce the thermal conductivity. Multiple aliovalent dopants result in a continually decreased carrier concentration and subsequent significantly decreased electrical conductivity. The Seebeck values are seen to increase with temperature, where a maximum value of ?171 ?V K?1is reported with a maximum power factor of ?22.7 ?W cm?1K?2. We show through first principles DFT calculations the synergistic effect of Bi and Sb to introduce resonance states and an additional valence band convergence effect with increasing Sb that contribute to improved electronic properties. A decreased phonon frequency with co-doping is also reported. A maximumZTof ?0.8 at 823 K is reported in the Sn0.90Bi0.03Sb0.10Te composition, showing good potential in Sb co-doped SnTe-based materials. © The Royal Society of Chemistry 2021.Item Probing of Bi doped GeTe thermoelectrics leads to revelation of resonant states(Elsevier Ltd, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.Quest for lead free high performance mid temperature thermoelectric materials has led to extensive research on SnTe and GeTe based materials. Among various strategies implemented to improve the transport properties of GeTe, electronic structure engineering holds a prominent place. Herein, we reinvestigate the impact of substitutional doping of Bi in GeTe on its electronic structure in both rhombohedral and cubic phase. We uncover that Bi introduces resonance levels in GeTe acting as a first n-type resonant dopant in both rhombohedral and cubic phases. We also report for the first time that Bi resonance states undergo Rashba splitting in low temperature rhombohedral phase. Bi doping acts in a multifunctional way by tuning the carrier concentration, causing conduction band convergence and phonon scattering in addition to improving the band effective mass by distorting the density of states near the Fermi level to enhance the thermoelectric performance of the material. The convergence of L, Z and Σ valence bands in rhombohedral phase due to Bi doping leads to manifestation of Rashba effect in p-type material which was not reported till date. Thus, we propose that the chemical potential tuning can result in p-type as well as n-type Bi doped GeTe for thermoelectric application. © 2022 Elsevier B.V.Item TeO2 for enhancing structural, mechanical, optical, gamma and neutron radiation shielding performance of bismuth borosilicate glasses(Elsevier Ltd, 2023) D'Souza, A.N.; Padasale, B.; Murari, M.S.; Karunakara, N.; Sayyed, M.I.; Elsafi, M.; Al-Ghamdi, H.; Almuqrin, A.H.; Kamath, S.D.The synthesized 12Bi2O3– 8BaO–12ZnO-0.5CeO2-17.5SiO2- (50-x) B2O3- xTeO2 glasses with x = 0, 10, 20, 30 and 40 mol% (coded BiTe-0 to BiTe-40) were investigated in terms of physical, structural, optical and mechanical properties to examine the influence of CeO2 and TeO2 on the heavy metal oxide (HMO) borosilicate network. Density values increased continuously with increasing TeO2 concentration with BiTe-40 glass exhibiting maximum value of 5.0875 gcm−3. This property helped in enhancement of refractive index values from 1.769 for BiTe-0 to 1.942 for BiTe-40. Fourier transform infrared (FTIR) analysis of studied glasses revealed the presence of additional small peak at 683 cm−1 in BiTe-30 and BiTe-40 which confirmed the formation of stable TeO4 units in the glass network. The deep brown colour of the glass existing due to bismuth's presence was nullified by CeO2 and TeO2 additives which improved transparency of the glass. Urbach analysis of these glasses led to optical bandgap variation between 3.27 eV and 2.73 eV for 0–40 mol% TeO2 concentration. Makishima and Mackenzie model was utilized for evaluation of elastic property of the glasses, and Poisson's ratio ranging between 1.935 and 1.953 was obtained. Vickers micro-indentation test on the current glasses revealed decreasing microhardness from 4.116 to 4.076 GPa with TeO2 variation from 0 to 40 mol% at 9.8 N load. Gamma radiation shielding parameters were determined using Phy-X/PSD software and it was found that BiTe-40 glass produce maximum MAC (mass attenuation co-efficient) values in high photon energy region 3.5–15 MeV. The present article also contains a detailed emphasis on behaviour of gamma radiation build-up factors at different incident photon energy and TeO2 concentration. The increasing trend of exposure build up factor (EBF) was seen with increasing penetration depth inside the samples at all energies, indicating that glasses of larger thickness improve the escape probability of photons. Meanwhile, fast neutron removal cross-section (FNRCS) was highest for BiTe-10 sample (0.10118 cm−1) which also surpassed the value of ordinary concrete (0.093 cm−1). Overall, the present glass system bested other conventional shields available commercially in terms of gamma and neutron radiation shielding effectiveness. © 2022 Elsevier B.V.Item A study on solubility of bismuth cations in nickel cobalt ferrite nanoparticles and their influence on dielectric and magnetic properties(Elsevier Ltd, 2023) Patil, S.; Meti, S.; Kanavi, P.S.; Bhajantri, R.F.; Anandalli, M.; Mondal, R.; Karmakar, S.; Muhiuddin, M.; Rahman, M.R.; Kumar, B.C.; Hegde, B.G.In this work, a low temperature (∼600 °C) solution combustion technique is employed for the synthesis of Ni0.5Co0.5BixFe2-xO4 (NCBFO, where x = 0.0, 0.05, 0.1, 0.15, & 0.2) nanoparticles with crystallite size variation of 17–22 nm. The X-ray diffraction (XRD) technique is used to confirm the formation of cubic spinel phase of Bi3+ doped (for x ≤ 0.05 samples) nickel–cobalt ferrite (NCFO) nanoparticles. The increase in bismuth substitution (x > 0.05) results in the formation of the Bi2O3 along with the NCFO structure, which results in the reduction of binding energy and is confirmed by the XRD and X-ray photoelectron spectroscopy (XPS) techniques. From the Raman spectra, the change in the intensities of the peaks is observed due to the variation of Bi3+ in NCFO matrix. Due to increasing cation concentration and electronegativity, the FTIR absorption band shifts toward the lower wave numbers. Dielectric measurements were carried out to examine the charge transport behavior and electric conduction mechanism. The FESEM images shows the non-magnetic bismuth atoms are diffused into the NCFO nanoparticles. From the vibrating sample magnetometer (VSM) analysis, it is observed that saturation magnetization, remanent magnetization, coercivity and squareness ratio are found to be maximum for x = 0.15 NCBFO sample. The high coercivity (Hc = 916.8 Oe) for the x = 0.15 sample indicates the hard ferromagnetic behaviour of the samples. © 2023 Elsevier B.V.Item Unveiling the Potential of Bismuth Oxy-Iodide (BiOI)-Based Photovoltaic Device for Indoor Light Harvesting(Institute of Electrical and Electronics Engineers Inc., 2023) Manjhi, S.; Siddharth, G.; Pandey, S.K.; Sengar, B.S.; Dwivedi, P.; Garg, V.Indoor photovoltaics (IPVs) have piqued the interest of many because of their potential to power small and portable electronics and photonic devices. This work investigates one of the exemplary perovskite inspired materials (PIMs), bismuth oxy-iodide (BiOI). In order to explore the potential of BiOI in the indoor environment, the baseline model of BiOI device [indium tin oxide (ITO)/NiOx/BiOI/ZnO/Contact] is developed using the experimental results of a recent study with a power conversion efficiency (PCE) of 4%. The performance of the proposed device is fine-tuned by investigating the effect of: 1) absorber thickness and defect density and 2) valence band offset (VBO) between the hole transport layer (HTL) and absorber interface (NiOx/BiOI) along with the interface defect density. Furthermore, the series and shunt resistance of the device is optimized. Additionally, the performance of the optimized device is investigated under different WLED light intensities. Finally, after optimizing the device under WLED illumination, the best performance parameters achieved are Jsc : 1.83 mA/cm2, Voc : 1.33 V, FF: 85.91%, and PCE: 40%. Moreover, the optimized device performance under different indoor light sources: WLED, halogen, and compact fluorescent lamps (CFLs), has been performed to estimate the performance under widely utilized lighting sources. © 1963-2012 IEEE.Item Rapid single pot synthesis of hierarchical Bi2WO6 microspheres/RGO nanocomposite and its application in energy storage: A supercritical water approach(Elsevier Ltd, 2023) Shetty, M.; Karnan, K.; Chetana, C.; Bekal, C.; Misnon, I.I.; P, A.; Roy, K.; Shivaramu, P.D.; Baloor, S.; Rangappa, D.The application of novel three-dimensional (3D) architectures in energy storage has fascinated researchers for a long time. The fast-paced technological advancements require reliable rapid synthesis techniques for developing multi-metal oxide (MMO) nanostructures. For the first time, we disclose the supercritical water method's use to synthesize a single-phase hierarchical three-dimensional (3-D) Bi2WO6 microsphere/Reduced Graphene Oxide (BWS/RGO) nanocomposite (SCW). Through various nano-characterization technologies, it is possible to confirm the sample characteristics and determine the nanocomposites' morphological, physical, and thermal properties. Additionally, the constructed coin cells' electrochemical behavior analyses shed light on their well-known higher initial cycle capacity of about 700 mAh g−1, demonstrating BWS nanostructures' superior capacity for lithium-ion storage (Li-ion). In contrast, in supercapacitor studies, a half-cell configuration with a 6 M KOH electrolyte achieved its maximum specific capacity of 1158C g−1 at a current density of 3 A g−1. Similarly, Trasatti's analysis shows that the false nature of the BWS/RGO material results in 83 % over capacitive behavior of 17 %. When it comes to effectively developing a material process technique for multi-metal oxides and associated RGO nanocomposites, the reported quick single-pot SCW approach has shown encouraging results. © 2023