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Венкатачалапатху, Вишнукантхан

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Цель ИЯФиТ и стратегия развития - создание и развитие научно-образовательного центра мирового уровня в области ядерной физики и технологий, радиационного материаловедения, физики элементарных частиц, астрофизики и космофизики.

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Венкатачалапатху

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Вишнукантхан

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Теперь показываю 1 - 10 из 22

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Heavy metal oxide glasses and their optoelectronic applications (infrared transmission, luminescence, nonlinear optical susceptibilities, etc.)
(2022) Mahalakshmi, S.; Mayandi, J.; Sagadevan, S.; Vajeeston, P.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
Glasses have attracted much technological and practical attention due to their unique physical and chemical properties, which depend on the structure that they accommodate. In particular, heavy metal oxide glasses have attracted the attention of many scientists due to the combination of their properties such as low melting temperatures, chemical durability and stability, a high dielectric constant, low phonon energy, a broad optical transmission window, and high linear and nonlinear refractive indices. One of their delightful properties is their strong nonlinear optical (NLO) behavior with which the materials are applicable for the fabrication of electronic devices, optical switches, optical waveguides, etc. Many organic, inorganic, and semiorganic materials with high polarizability are understood to be suitable candidates for the NLO study. Yet, the total polarization of the material hinges on its non-centrosymmetric properties, which were originally formed by the direction of the interrupting field. The growing interest in bismuthate glasses is due to their promising applications in the field of optoelectronics and nonlinear optics as photonic switches. They exhibit third-harmonic generation due to their low melting temperatures, extensive glass formation range, physical stability, high refractive index, and high nonlinear optical susceptibility. Similarly, tellurite glasses have gained much importance for their exclusive properties such as a broad optical transmission window, a high dielectric constant, low phonon energy, and high linear and nonlinear refractive indices. Similarly, germanium oxide glasses are also preferred in many optoelectronic uses for various purposes including optical and radiation applications. In this chapter, we will address the optical properties, the second-harmonic generation property toward NLO applications, and radiation-shielding properties of heavy metal oxides and their compositional glasses using various characterization techniques. Besides, computational studies will also be included to shed light on the origin of the enhanced optical properties in terms of physics. © 2022 Elsevier Inc. All rights reserved.
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Fabrication and Characterization of Si/PEDOT: PSS-Based Heterojunction Solar Cells
(2022) Venkatesan, R.; Maideen, S. M. T. S. K.; Chandhiran, S.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
In this study, we fabricated a planar Si/PEDOT: PSS heterojunction solar cell using three different solventsвЂ”ethylene glycol, acetonitrile, and dimethyl sulfoxideвЂ”to find the best one. The fabricated samples were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X-ray diffraction, and currentвЂ“voltage. Diffused reflectance spectrum analysis showed reduced reflectance compared to the bare silicon wafers. The absorbance spectrum shows the change in absorption of the Si-coated PEDOT: PSS which was more than a 50% increase in the UV region, and for the EG sample, there was a 20% increase in the entire visible spectrum. This indicates that the solvent plays a major role in the bandgap between the Si and Si/PEDOT: PSS. Scanning electron microscope (SEM) was used to examine the surface morphology of Si/PEDOT: PSS as agglomerated, island-formed surfaces and carbon-layered Si-PEDOT: PSS. Cross-sectional images show the thickness of the PEDOT: PSS layer on the silicon wafer surface. The X-ray diffraction (XRD) pattern shows the characteristic peaks for silicon (69.5В°), and Si/PEDOT: PSS shows a forbidden Si (200) peak at 32В°. CurrentвЂ“voltage measurements have shown the characteristic diode curve for all fabricated cells. This characteristic diode curve indicated the presence of a heterojunction. Ethylene glycol-containing cells showed current output as 0.2 ОјA with Voc of 0.2 V.
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Enriched second-harmonic generation in meta-phase barium titanate nanostructures synthesized by sol-gel hydrothermal method
(2023) Mahalakshmi, S.; Mayandi, J.; Sagadevan, S.; Ragavendran, V.; Manikandan, K.; Arumugam, S.; Pearce, J. M.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
This study reports on the second harmonic generation (SHG) of barium titanate (BaTiO3) nanoparticles synthesized by a low-cost and easily-accessible sol-gel hydrothermal method at different temperatures (100–250 °C). According to the powder X-ray diffraction (XRD) pattern, all of the prepared samples had meta-phase without a center of symmetry, and the crystal structure changes from simple cubic to rhombohedral at different temperatures. In addition to XRD, differential scanning calorimetry (DSC) confirms the meta-phase in BaTiO3 by showing a significant phase shift indicating structural distortion. The variation in particle size was observed from transmission electron microscope (TEM) and the selected area electron diffraction (SAED) pattern as well supports the presence of structural distortion in the nanomaterials. The phase variation in BaTiO3 has not only affected its structure but also creates a disorder in its magnetic properties by changing it from paramagnetic to ferromagnetic for different synthesizing temperatures. This was determined with a vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) techniques. As a consequence of this structural deformation, particle size variation, and magnetic phase transition the second harmonic generation (SHG) conversion efficiency of BaTiO3 has been improved. Hence, this technique for synthesizing nanomaterials could be a promising candidate for fabricating bio-compatible imaging probes and coherent bio-markers in the field of medicine and electronics. © 2022 Elsevier B.V.
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Influence of tin (IV) doping on structural and optical properties of rhombohedral barium titanate (BaTiO3)
(2019) Selvaraj, M.; Venkatesan, R.; Mayandi, J.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
© 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the Exploring Nanostructures for Enhanced Power Conversion Efficiency of Solar Cells Conference.The impact of tin (IV-Sn4+) doping into rhombohedral barium titanate (BaTiO3) towards the enhancement of second harmonic generation (SHG) was studied. XRD analysis confirms retention of rhombohedral symmetry in Sn4+ doped BaTiO3. UV-Vis absorption study reveals that Sn4+ doping has no significant effect on the optical band gap of BaTiO3. Raman spectrum portrays that undoped and Sn4+ doped BaTiO3 nanopowder exhibits Raman active modes of rhombohedral symmetry. The studies displays that Sn4+ doped BaTiO3 has created non-centrosymmetry, which could be utilized for enhancement in SHG and possibility to improve the efficiency in rhombohedral BaTiO3 based solar cells.
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Al-doped ZnO prepared by co-precipitation method and its thermoelectric characteristics
(2021) Mayandi, J.; Madathil, R. K.; Abinaya, C.; Bethke, K.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
© 2021 Elsevier B.V.We report on structural and electrical characterization of zinc oxide material containing aluminum (Al:ZnO) prepared by a co-precipitation technique using different zinc and aluminum precursors. The as-prepared powders were calcinated and pre-annealed at 600 °C and 1200 °C. These were cold-pressed to pellets and sintered at 1000 °C. We also prepared ZnO material with no Al for comparisons. The electrical and thermal conductivity, as well as the Seebeck coefficient, were measured. These properties were correlated with structural analysis by X-ray diffraction characterization and scanning electron microscopy. The process yields a nanostructured material with much reduced thermal conductivity.
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Activation energy of silicon diffusion in gallium oxide: Roles of the mediating defects charge states and phase modification
(2021) Azarov, A.; Vines, L.; Monakhov, E.; Lee, I. -H.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
© 2021 Author(s).Silicon (Si) is an efficient n-type dopant in gallium oxide (Ga2O3) - an ultra-wide bandgap semiconductor promising in a number of applications. However, in spite of the technological importance for device fabrication, the activation energy for Si diffusion in Ga2O3 is missing in the literature. In the present work, we do such measurements in ion implanted monoclinic β-Ga2O3 samples employing anneals in air ambient, also admitting the influence of potential ion beam induced phase modifications on diffusion. Importantly, we show that Si diffusion in β-Ga2O3 fits with the concentration dependent diffusion model, involving neutral and single negatively charged point defects to mediate the process; so that we assumed gallium vacancies in the corresponding charge states to assist Si diffusion in β-Ga2O3 with activation energies of 3.2 ± 0.3 and 5.4 ± 0.4 eV, respectively. Moreover, we also found that a preexisting phase modified surface layer efficiently suppressed Si diffusion in β-Ga2O3 for temperatures up to 1000 °C.
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Radiation-induced defect accumulation and annealing in Si-implanted gallium oxide
(2022) Kjeldby, S. B.; Azarov, A.; Nguyen, P. D.; Venkatachalapathy, V.; Mikšová, R.; MacKová, A.; Kuznetsov, A.; Prytz, O.; Vines, L.; Венкатачалапатху, Вишнукантхан
Defect accumulation and annealing phenomena in Si-implanted monoclinic gallium oxide (ОІ-Ga2O3) wafers, having (2ВЇ01), (010), and (001) orientations, were studied by Rutherford backscattering spectrometry in channeling mode (RBS/c), x-ray diffraction (XRD), and (scanning) transmission electron microscopy [(S)TEM]. Initially, the samples with different surface orientations were implanted with 300 keV 28Si+-ions, applying fluences in the range of 1 Г— 1014вЂ“2 Г— 1016 Si/cm2, unveiling interesting disorder accumulation kinetics. In particular, the RBS/c, XRD, and (S)TEM combined data suggested that the radiation disorder buildup in Si-implanted ОІ-Ga2O3 is accompanied by significant strain accumulation, assisting crystalline-to-crystalline phase transitions instead of amorphization. Selected samples having (2ВЇ01) orientation were subjected to isochronal (30 min) anneals in the range of 300вЂ“1300 В°C in air. Systematic RBS/c and XRD characterization of these samples suggested complex structural transformations, which occurred as a function of the fluence and the temperature. Moreover, a detailed (S)TEM analysis of the sample implanted with 2 Г— 1016 Si/cm2 and annealed at 1100 В°C was enhanced by applying dispersive x-ray and electron energy-loss spectroscopies. The analysis revealed silicon agglomerations in the form of silicon dioxide particles. Signal from silicon was also detected outside of the agglomerates, likely occurring as substitutional Si on Ga sites.
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Correlations of thermal properties with grain structure, morphology, and defect balance in nanoscale polycrystalline ZnO films
(2021) Kazmierczak-Balata, A.; Grzadziel, L.; Guziewicz, M.; Kuznetsov, A.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
© 2021 Elsevier B.V.Two sets of ZnO thin films grown by atomic layer deposition method were investigated to analyse the correlation between morphology, chemical defects and thermal properties. This analysis became possible by measuring series of similarly thick wurtzite ZnO films synthesized using identical number of deposition cycles at two temperatures – 100 °C and 200 °C. By comparing these sample series, exhibiting the thickness variations from 12 to 118 nm, we observed several prominent correlations for the thermal properties as measured by high-resolution scanning thermal microscopy at room temperature. Specifically, comparing thinnest samples in the series, a lower thermal conductivity was revealed in samples grown at 100 °C and these variations were interpreted in terms of changing populations of native donors, affecting the free carrier concentration and, as such, the thermal conductivity. Further, the increase in thickness for the samples grown at 200 °C was accompanied with a continuous shift to Zn-rich conditions and the corresponding increase in the thermal conductivity, specifically from 0.28 Wm−1 K−1 to 2.81 Wm−1 K−1. As such, we have decoupled the thickness effect on the thermal conductivity from the rest of the phenomena, explaining the thermal transport in terms of the bulk thermal contributions within the grains combined with additional thermal resistance introduced by the grain boundaries.
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Interplay of the disorder and strain in gallium oxide
(2022) Azarov, A.; Venkatachalapathy, V.; Karaseov, P.; Titov, A.; Karabeshkin, K.; Struchkov, A.; Kuznetsov, A.; Венкатачалапатху, Вишнукантхан
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Disorder-Induced Ordering in Gallium Oxide Polymorphs
(2022) Azarov, A.; Bazioti, C.; Vajeeston, P.; Monakhov, E.; Venkatachalapathy, V.; Венкатачалапатху, Вишнукантхан
© 2022 American Physical SocietyPolymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga2O3 and, potentially, for similar polymorphic families in other materials.