Faculty Publications
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Item Enhancement of quantum capacitance by chemical modification of graphene supercapacitor electrodes: a study by first principles(Indian Academy of Sciences, 2019) Sruthi, T.; Tarafder, K.In this paper, we specify a powerful way to boost quantum capacitance of graphene-based electrode materials by density functional theory calculations. We performed functionalization of graphene to manifest high-quantum capacitance. A marked quantum capacitance of above 420?Fcm-2 has been observed. Our calculations show that quantum capacitance of graphene enhances with nitrogen concentration. We have also scrutinized effect on the increase of graphene quantum capacitance due to the variation of doping concentration, configuration change as well as co-doping with nitrogen and oxygen ad-atoms in pristine graphene sheets. A significant increase in quantum capacitance was theoretically detected in functionalized graphene, mainly because of the generation of new electronic states near the Dirac point and the shift of Fermi level caused by ad-atom adsorption. © 2019, Indian Academy of Sciences.Item Enhanced photocatalytic efficiency of layered CdS/CdSe heterostructures: Insights from first principles electronic structure calculations(Institute of Physics Publishing helen.craven@iop.org, 2020) Shenoy, S.; Tarafder, K.Metal sulfides are emerging as an important class of materials for photocatalytic applications, because of their high photo responsive nature in the wide visible light range. In this class of materials, CdS with a direct band gap of 2.4 eV, has gained special attention due to the relative position of its conduction band minimum, which is very close to the energies of the reduced protons. However, the photogenerated holes in the valence band of CdS are prone to oxidation and destroy its structure during photocatalysis. Thus constructing a CdS based heterostructure would be an effective strategy for improving the photocatalytic performance. In this work we have done a detail theoretical investigation based on hybrid density functional theory calculation to get insight into the energy band structure, mobility and charge transfer across the CdS/CdSe heterojunction. The results indicate that CdS/CdSe forms type-II heterostructure that has several advantages in improving the photocatalytic efficiency under visible light irradiation. © 2020 IOP Publishing Ltd.Item Spin transport through metal-dichalcogenides layers: a study from first-principles calculations(IOP Publishing Ltd, 2020) Devaraj, N.; Tarafder, K.Spin transport through monolayer and trilayers of molybdenum dichalcogenides were studied considering Co as leads. Detailed investigations of the electronic structure of the Co/MoS2 interface and magnetic tri-junctions are carried out by using density functional theory calculations to understand transport behavior. The study revealed that new spin-polarized hybridized states appeared at the Fermi level due to the formation of Co/MoS2 interface that effectively acted as a spin filter and enhanced the spin injection efficiency of the systems. Spin-polarized current through the system as well as the magnetoresistance (MR) was estimated at different applied bias voltages. Large MR up to 78% was calculated for the trilayer MoS2 system at a relatively high applied bias voltage. The MR values are further improved by tuning the structure of the scattering region. A very large MR of 123% for MoS2/MoSe2/MoS2 trilayer at an applied bias 0.8 V was observed, which is much higher than the previously reported bias dependent MR values in similar systems. © 2020 IOP Publishing Ltd.Item Enhanced quantum capacitance in chemically modified graphene electrodes: Insights from first principles electronic structures calculations(Elsevier B.V., 2021) Sruthi, T.; Tarafder, K.We have carried out a systematic study of quantum capacitance in functionalized graphenes by using DFT calculations. The graphene functionalization has been done by doping with different aliphatic and aromatic molecules and their radicals. The quantum capacitance of functionalized graphenes was estimated from the accurate electronic band structures of the system obtained by using DFT calculations. Our theoretical investigation reveals that aromatic and aliphatic radicals introduce localized density of states near the Fermi level of the functionalized systems, due to a charge localization. As a result, a very high quantum capacitance (>230?F?cm2) was observed in the system. The effects of atomic dislocation and the vacancy defect on graphene during functionalization has also been incorporated in our investigation. Our study suggests an effective way to synthesize highly efficient graphene-based supercapacitor electrode materials by using aromatic and aliphatic molecule/ radical functionalization of graphene. © 2020 Elsevier B.V.Item Large magnetoresistance in a Co/Mo S2/graphene/Mo S2/Co magnetic tunnel junction(American Physical Society, 2021) Devaraj, N.; Tarafder, K.We demonstrate a large magnetoresistance (MR) in a Co/MoS2/graphene/MoS2/Co magnetic tunnel junction by means of ab initio transport calculations. A Co electrode turns out to be an excellent spin injector for a MoS2/graphene/MoS2 barrier. The transmission spectrum, current-voltage characteristics, spin injection efficiency, and magnetoresistance are calculated for the modeled device at various bias voltages in the parallel and antiparallel magnetic configurations. A remarkable change in the transmission spectrum and a subsequent change in total current through the junction have been observed, when the relative magnetic orientations of the electrodes are altered. The huge change in current due to the change in the relative magnetic orientation of the Co electrodes produces a high magnetoresistance up to 1270%. The obtained values of the device parameters clearly indicate that a MoS2/graphene/MoS2 heterostructure would be an excellent compound for highly efficient spin-valve device applications. © 2021 American Physical Society.Item Unprecedented Electroreduction of CO2over Metal Organic Framework-Derived Intermetallic Nano-Alloy Cu0.85Ni0.15/C(American Chemical Society, 2022) Payra, S.; Devaraj, N.; Tarafder, K.; Roy, S.Designing suitable catalysts for efficient and selective electrocatalytic reduction of CO2 is a need of the hour, and in this regard, the well-defined, highly dispersed active metal centers can be a trendsetting research endeavor toward CO2 electroreduction due to the maximum atom utilization and unique electronic structure. This study describes the synthesis and electrocatalytic CO2 reduction activity of atomistically dispersed Cu/C and Ni/C and the intermetallic nano-alloy Cu0.85 Ni0.15 /C. The catalysts were synthesized from the corresponding MOF precursors. The successful synthesis of the monometallic and intermetallic nano-alloys was established from structural, surface morphological, and electronic properties. Cu0.85 Ni0.15 /C exhibited an unprecedented electrocatalytic reduction of CO2 with a high selectivity and high faradaic efficiency toward CH3 OH. The kinetic studies and the first-principles calculations elucidated the intricate mechanism and the superior activity of electrocatalytic reduction of CO2 over the intermetallic Cu0.85 Ni0.15 /C catalyst. © 2022 American Chemical Society. All rights reserved.Item Spin-Transport through Van der Waals Heterojunctions Based on 2D-Ferromagnet and Transition Metal Dichalcogenides: A Study from First-Principles Calculations(John Wiley and Sons Inc, 2022) Devaraj, N.; Tarafder, K.Recently reported 2D ferromagnets show tremendous potential for their application in low-dimensional spintronic devices. Semiconductor heterostructure consisting of 2D ferromagnet integrated with other suitable 2D semiconducting materials may pave the way for designing robust and sophisticated spin-transport devices within a few nanometer scales. In this regard, a detailed understanding of the interface properties of 2D ferromagnetic materials and other 2D semiconductors is highly essential. Herein, the interface properties in the heterostructure made-up of CrX3 (X = Cl, Br, and I) monolayer and transition-metal dichalcogenides (TMDC; MoS2, MoSe2, and WS2) monolayer, using first-principle calculations are systematically studied. This study predicts that a robust spin-dependent barrier originated at the CrX3/TMDC interface. It can lead to a significantly large spin-filtering at the interface while spin-transport through this heterojunction, which will be highly beneficial for spintronic devices applications. Further, detailed spin-dependent transport studies carried out through Co/CrI3/TMDC/CrI3/Co magnetic heterojunctions and substantial tunnel magnetoresistance up to 590%, estimated for these systems. © 2022 Wiley-VCH GmbH.Item Magnetic complexity, magnetodielectric effect and DFT calculations on correlation driven Gd2CoMnO6 insulator(Elsevier B.V., 2022) Prashanth, C.H.; Reddy, I.; Tarafder, K.; Chandrasekhar Kakarla, D.; Yang, H.D.; Adyam, V.; Jyothinagaram, K.In the family of Re2CoMnO6 manganite double perovskites, in contrast to parent La2CoMnO6 compound, Gd2CoMnO6 exhibits multiple magnetic transitions; ferromagnetic (FM) ordering, TC ∼ 112 K followed by AFM transition, TN ∼ 47 K, Gd spins ordering for T < 10 K and large isothermal entropy changes. A study of DC field-superimposed AC magnetic susceptibility measurements revealed the field-induced magnetic glassy behavior below TC and enhancement of FM correlations above TC. From the analysis of Almeida-Thouless behavior and dynamical power-law fit to frequency dependent AC susceptibility, Gd2CoMnO6 exhibits a volume spin glass-like nature below the freezing temperature, Tf ∼ 117.5 K. The isothermal field-dependent magnetic and dielectric permittivity data and temperature dependent Raman measurements (reported in ref. R. X. Silva et al., J, Appl. Phys. 114 194,102 (2013)) confirms the spin-phonon coupling induced magnetodielectric effect. Further, the ground-state electronic structure and magnetic properties of Gd2CoMnO6 are investigated using DFT + U formalism with Vienna Ab-initio Simulation Package (VASP) code and predicted the material to be a correlation-driven insulator. The correlation value of the Hubbard U parameter at the 4f-Gd elements changes the stability of the magnetic state from Ferri to FM spin alignment for Ueff ≥ 3 eV and is correlated to the experimentally observed field-induced transformation of the short-range-order FiM/spin-glass-like phase into the long-range ordered FM phase. © 2022