Browsing by Author "Devaraj, N."

Now showing 1 - 6 of 6

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.
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.
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.
The role of synthesis vis-à-vis the oxygen vacancies of Co3O4 in the oxygen evolution reaction
(Royal Society of Chemistry, 2022) Roy, S.; Devaraj, N.; Tarafder, K.; Chakraborty, C.; Roy, S.
The oxygen evolution reaction over oxide vacancy-induced spinel Co3O4 is a topic of tremendous scientific attention owing to the favourable adsorption of water, as also shown here through DFT calculations. However, the inclusion of an optimum amount of oxygen-ion vacancies at the surface and in the bulk of Co3O4 remains a synthetic challenge in order to enhance the efficacy of the oxygen evolution reaction. Here, we have attempted a single-step scalable approach of solution combustion synthesis to incorporate the oxide ion vacancies in high-surface-area Co3O4. To benchmark the catalyst, we also synthesized Co3O4 using elevated-temperature calcination routes. Detailed structural and surface analyses revealed the significant presence of oxide ion vacancies in the combustion-synthesized material. The solution combustion synthesized Co3O4 due to the presence of oxygen-ion vacancies exhibited an excellent oxygen evolution reactivity with a lower overpotential and higher current density compared with the other Co3O4 materials synthesized using calcination routes. Tafel slope calculations indicated that the formation of surface hydroxyl species through water dissociation over the oxide ion vacancies is the rate-determining step of the overall reaction. The mechanistic role of the oxygen-ion vacancies in the oxygen evolution reaction was further explored via DFT studies. © 2022 The Royal Society of Chemistry
Theoretical investigation of quantum capacitance in the functionalized MoS2-monolayer
(IOP Publishing Ltd, 2021) Sruthi, T.; Devaraj, N.; Tarafder, K.
In this work, we investigated the electronic structure and the quantum capacitance of a set of functionalized MoS2 monolayers. The functionalizations have been done by using different ad-atom adsorption on MoS2 monolayer. Density functional theory calculations are performed to obtain an accurate electronic structure of ad-atom doped MoS2 monolayer with a varying degree of doping concentration. Subsequently, the quantum capacitance in each functionalized system was estimated. A marked quantum capacitance above 200 ?F cm-2 has been observed. Our calculations show that the quantum capacitance of MoS2 monolayer is significantly enhanced with substitutional doping of Mo with transition metal ad-atoms. The microscopic origin of such enhancement in quantum capacitance in this system has been analyzed. Our DFT-based calculation reveals that the generation of new electronic states at the proximity of the band-edge and the shift of Fermi level caused by the ad-atom adsorption results in a very high quantum capacitance in the system. © 2021 Institute of Physics Publishing. All rights reserved.
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.