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Item Memory type switching behavior of ternary Ge20Te80-xSnx (0 x 4) chalcogenide compounds(Institute of Physics Publishing michael.roberts@iop.org, 2016) Fernandes, B.J.; Sridharan, K.; Pumlianmunga, P.; Ramesh, K.; Udayashankar, N.K.Chalcogenide compounds have gained huge research interest recently owing to their capability to transform from an amorphous to a crystalline phase with varying electrical properties. Such materials can be applied in building a new class of memories, such as phase-change memory and programmable metallization cells. Here we report the memory type electrical switching behavior of a ternary chalcogenide compound synthesized by doping Tin (Sn) in a germanium-telluride (Ge20Te80) host matrix, which yielded a composition of Ge20Te80-xSnx (0 x 4). Results indicate a remarkable decrease in the threshold switching voltage (V T) from 140 to 61 V when the Sn concentration was increased stepwise, which is attributed to the domination of the metallicity factor leading to reduced amorphous network connectivity and rigidity. Variation in the threshold switching voltage (V T) was noticed even when the sample thickness and temperature were altered, confirming that the memory switching process is of thermal origin. Investigations using x-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed the formation of a crystalline channel that acts as the conduction path between the two electrodes in the switched region. Structural and morphological studies indicated that Sn metal remained as a micro inclusion in the matrix and hardly contributed to the rigid amorphous network formation in Ge20Te80-xSnx. Memory type electrical switching observed in these ternary chalcogenide compounds synthesized herein can be explored further for the fabrication of phase-change memory devices. © 2016 IOP Publishing Ltd.Item Crystallization kinetics of Sn doped Ge20Te80?xSnx (0 ? x ? 4) chalcogenide glassy alloys(Elsevier Ltd, 2017) Fernandes, B.J.; Naresh, N.; Ramesh, K.; Sridharan, K.; Udayashankar, N.K.Chalcogenide semiconductors have evolved as multifunctional materials due to their fascinating thermal, optical, electrical and mechanical properties. In this report, Ge20Te80?xSnx (0 ? x ? 4) glassy alloys are systematically studied in order to understand the effect of variation of Sn content on the thermal parameters such as glass transition (Tg) onset crystallization (Tc), peak crystallization (Tp), melting temperature (Tm), activation energy of glass transition (Eg), and crystallization (Ec). The values of Eg are calculated from the variation of Tg with the heating rate (?), according to Kissinger and Moynihan model, while the values of Ec are calculated from the variation of Tp with the heating rate (?), according to Kissinger, Takhor, Augis-Bennett and Ozawa model. Thermal stability and glass forming ability (GFA) are discussed for understanding the applicability of the synthesized materials in phase change memory (PCM) applications. Thermal parameters are correlated with the electrical switching studies to get an insight into the phase change mechanism. The results of the calculated thermal parameters reveal that the GFA of the synthesized Ge20Te80?xSnx (0 ? x ? 4) glassy alloys has a synchronous relationship with their thermal properties studied through differential scanning calorimetry, indicating their potential for phase-change memory device applications. © 2017 Elsevier B.V.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 Gamma irradiation effect on structural, optical and electrical properties of organometallic potassium hydrogen oxalate oxalic acid dihydrate single crystal(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Mahendra, K.; Nayak, K.K.; Fernandes, B.J.; Udayashankar, N.K.Potassium oxalate oxalic acid dihydrate (KHO) single crystals were grown from solvent evaporation technique at room temperature. Crystals were optically characterized using UV–Vis and photoluminescence analysis. The gamma irradiation effects on KHO crystals were also studied optically and the results were analyzed to compare the effect of irradiation on the crystal lattice for different dosage. Structural variations were studied using powder XRD, FTIR and the results were examined to study the defect states created inside the lattice due to irradiation and the effect on the functional vibrations of the host crystal. Surface morphology of the crystal was studied using scanning electron microscope (SEM). Photo conductivity of the synthesized crystals were studied and analyzed to compare the photo response as well as the conductivity of the materials when subjected to irradiation. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.Item Crystallization kinetics of Si20Te80?xBix (0???x???3) chalcogenide glasses(Elsevier Ltd, 2019) Fernandes, B.J.; Ramesh, K.; Udayashankar, N.K.In this report, we investigate the crystallization kinetics of Si20Te80?xBix (0 ? x ? 3) chalcogenide glassy systems using differential scanning calorimetry (DSC) technique. Systematic studies are carried out in order to understand the variation of thermal parameters such as glass transition temperature (Tg), onset crystallization temperature (Tc) and peak crystallization temperature (Tp) as a function of composition. Activation energy for glass transition (Eg) and crystallization (Ec) has been calculated based on the relevant statistical methods. Furthermore, thermal parameters such as change in specific heat (?Cp), fragility index (F), thermal stability (?T)& (S), enthalpy (?Hc), entropy (?S) are deduced to interpret distinct material behaviour as a function of composition. Structural evaluation like thermal devitrification studies elucidate the restricted glass formability of the studied glass system. Conclusively, a relationship has been established between the obtained thermal parameters and electrical switching characteristics. © 2019 Elsevier B.V.Item 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 Systematic investigation and comparison of oxalic acid dihydrate, ammonium oxalate hydrate and ammonium hydrogen oxalate oxalic acid dihydrate single crystals(Elsevier Ltd, 2023) Mahendra, K.; Fernandes, B.J.; Pattar, J.; Pujar, S.; Nagaraja, B.S.; Ramesh, K.P.; Udayashankar, N.K.Semiorganic crystals are hybrid materials that have captured the interest of researchers due to their improved material characteristics and applications. In the current work, single crystals of oxalic acid dihydrate (OAD), Ammonium oxalate hydrate (AHO), and Ammonium hydrogen oxalate oxalic acid dihydrate (AHOOD) were grown using a slow evaporation method. Single crystal and powder XRD measurements were carried out to elucidate their unit cell parameters, crystal system, and structural information. To comprehend the interplay of light and matter, optical investigations like UV–Vis Spectroscopy and photoluminescence studies were performed. Interaction of ammonium with oxalic acid, and thus formed crystals, was investigated using impedance spectroscopy. Detailed dielectric parameters such as dielectric constant, dielectric loss, impedance, conductivity, and electric modulus were explored as a function of frequency. Vickers hardness test was used to calculate the hardness, Meyer's number, brittleness, and fracture toughness. The crystals were determined to be of the hard materials group. © 2022 Elsevier B.V.