Browsing by Author "Kushwaha A.K."

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Band gap modulation of graphene by metal substrate: A first principles study
(2018) Sahoo M.R.; Sahu S.; Kushwaha A.K.; Nayak S.K.
Due to high in-plane charge carrier mobility with high electron velocity and long spin diffusion length, graphene guarantees as a completely unique material for devices with various applications. Unaffected 2pz orbitals of carbon atoms in graphene can be highly influenced by substrates and leads to tuning in electronic properties. We report here a density functional calculation of graphene monolayer based on metallic substrate like nickel surfaces. Band-gap of graphene near K points opens due to interactions between 2pz and d-orbitals of nickel atoms and the gap modulation can be done with the increasing number of layers of substrates. � 2018 Author(s).
Charge transfer and hybridization effect at graphene-nickel interface: A tight binding model study
(2019) Sahu S.; Sahoo M.R.; Kushwaha A.K.; Rout G.C.; Nayak S.K.
We have investigated here, the electronic and magnetic properties of graphene�nickel system by tight-binding mean-field approach. Strong hybridization between the 2pz orbital of graphene and 3dz2 orbital of nickel occurs when monolayer graphene is placed over a single layer of ferromagnetically ordered Ni (111) metal due to the excellent lattice matching between the two layers. This hybridization greatly affects the electronic and magnetic properties of the bilayer system, resulting in a significantly reduced local magnetic moment of the nickel layer and an enhanced induced spin polarization on the graphene layer. The calculated Hamiltonian revealed critical information regarding the first-, second-and third-nearest-neighbour hopping integrals of ?? electrons of graphene besides the Coulomb correlation of electrons in nickel (111). The Hubbard type Coulomb interactions present in nickel lattices were treated within the mean-field approximation. Zubarev's technique was employed to calculate electronic Green's functions and subsequent investigation of the temperature dependent ferromagnetic magnetization of nickel (111)was carried out through self-consistent calculation. Further calculations regarding the induced magnetization in the graphene, total magnetization in bilayer layer system, electronic band dispersion, spin resolved density of states (DOS) and spin polarization efficiency have been carried out. The results were corroborated by experimental observations. � 2018 Elsevier Ltd
Engineering Redox Potential of Lithium Clusters for Electrode Material in Lithium-Ion Batteries
(2017) Kushwaha A.K.; Sahoo M.R.; Nanda J.; Nayak S.K.
Low negative electrode potential and high reactivity makes lithium (Li) ideal candidate for obtaining highest possible energy density among other materials. In this work we show a novel route with which the overall electrode potential could significantly be enhanced through selection of cluster size. Using first principles density functional theory and continuum dielectric model, we studied free energy and redox potential as well as investigated relative stability of Lin (n�?�8) clusters in both gas phase and solution. We found that Li3 has the lowest negative redox potential (thereby highest overall electrode potential) suggesting that cluster based approach could provide a novel way of engineering the next generation battery technology. The microscopic origin of Li3 cluster�s superior performance is related to two major factors: gas phase ionization and difference between solvation free energy for neutral and positive ion. Taken together, the present study provides insight into the engineering of redox potential in battery and could stimulate further work in this direction. � 2017, Springer Science+Business Media, LLC.
First-principles study of a vertical spin switch in atomic scale two-dimensional platform
(2019) Sahoo M.R.; Kushwaha A.K.; Pati R.; Ajayan P.M.; Nayak S.K.
High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique material for spin-based devices. However, in a vertical graphene junction, the 2pz orbitals of carbon atoms in graphene can be tuned via suitable magnetic substrates; this would affect the spin injection into graphene. Here, a vertical spin switch has been designed by embedding a single layer of graphene as a tunnel layer between the Ni (1 1 1) substrate. Periodic density functional approach in conjunction with Julliere's model is used to calculate the tunnel magnetoresistance (TMR). Further, single-layered hexagonal Boron Nitride (h-BN) is sandwiched between the graphene and Ni (1 1 1) substrate to understand the role of hybridization at the interface on TMR. Our calculation shows that in contrast to the graphene junction, a much higher TMR value is obtainable in the case of the graphene/h-BN multi-tunnel junction (MTJ). The TMR in graphene junction is found to decrease with the increase of an externally applied electric field, and drops to zero for a field greater than equal to 0.16 V/�. Similar phenomenon was observed in the case of h-BN/graphene MTJ, where TMR value remains unchanged for electric field up to 0.1 V/� beyond which it drops to zero. The change in hybridization and charge-carrier-population at the interface modifies the magnetic exchange interaction and magnetic anisotropy resulting in a spin flip at interface, leads to rapid drop in TMR after a threshold electric field. The high and tunable TMR value suggests h-BN assisted high performance graphene based vertical spin switch. � 2019
Probing potential Li-ion battery electrolyte through first principles simulation of atomic clusters
(2018) Kushwaha A.K.; Sahoo M.R.; Nayak S.
Li-ion battery has wide area of application starting from low power consumer electronics to high power electric vehicles. However, their large scale application in electric vehicles requires further improvement due to their low specific power density which is an essential parameter and is closely related to the working potential windows of the battery system. Several studies have found that these parameters can be taken care of by considering different cathode/anode materials and electrolytes. Recently, a unique approach has been reported on the basis of cluster size in which the use of Li3 cluster has been suggested as a potential component of the battery electrode material. The cluster based approach significantly enhances the working electrode potential up to ?0.6V in the acetonitrile solvent. In the present work, using ab-initio quantum chemical calculation and the dielectric continuum model, we have investigated various dielectric solvent medium for the suitable electrolyte for the potential component Li3 cluster. This study suggests that high dielectric electrolytic solvent (ethylene carbonate and propylene carbonate) could be better for lithium cluster due to improvement in the total electrode potential in comparison to the other dielectric solvent. � 2018 Author(s).
Study of electronic and magnetic properties of h-BN on Ni surfaces: A DFT approach
(2018) Sahoo M.R.; Sahu S.; Kushwaha A.K.; Nayak S.
Hexagonal boron nitride (h-BN) is a promising material for implementation in spintronics due to large band gap, low spin-orbit coupling, and a small lattice mismatch to graphene and close-packedsurfaces of fcc-Ni(111). Electronic and magnetic properties of single layer hexagonal Boron Nitride (h-BN) on Ni (111) surface have been studied with density functional calculation. Since lattice constants of nickel surfaces are very close to that of h-BN, nickel acts as a good substrate. We found that the interaction between 2Pz - 3dz2 orbitals leads to change in electronic band structure as well as density of states which results spin polarization in h-BN. � 2018 Author(s).
Understanding the Role of Fluorination on the Interaction of Electrolytic Carbonates with Li+ through an Electronic Structure Approach
(2019) Kushwaha A.K.; Sahoo M.R.; Nayak S.K.
The donor-acceptor orbital interaction between the unoccupied orbital of Li+ and the lone pair of oxygen atoms in the carbonyl group of Li+-carbonate complexes shows significant decrease on fluorination. This has been investigated through molecular orbital formalism based density functional theory. The fluorination process lowers the binding energy (reduced up to 13.8 kcal/mol), and widens the HOMO-LUMO gap (enhanced up to 0.7 eV), which is essential for achieving electrolytes with high potential window in Li-ion battery. Furthermore, the impact of fluorination on few critical factors has been observed, i. e. dipole moment (drastic enhancement), IR spectra (most affected C=O vibrational mode shows blue shift in the spectra) and Raman active mode (carbonyl group stretching mode doublet (vC<C=>O) shifted to higher frequency) which have been probed by vibrational frequency analysis. � 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Wobbled electronic properties of lithium clusters: Deterministic approach through first principles
(2018) Kushwaha A.K.; Nayak S.K.
The innate tendency to form dendritic growth promoted through cluster formation leading to the failure of a Li-ion battery system have drawn significant attention of the researchers towards the effective destabilization of the cluster growth through selective implementation of electrolytic media such as acetonitrile (MeCN). In the present work, using first principles density functional theory and continuum dielectric model, we have investigated the origin of oscillatory nature of binding energy per atom of Lin (n ? 8) under the influence of MeCN. In the gas phase, we found that static mean polarizability is strongly correlated with binding energy and shows oscillatory nature with cluster size due to the open shell of Lin cluster. However, in acetonitrile medium, the binding energy has been correlated with electrostatic Lin?MeCN interaction and it has been found that both of them possess wobbled behavior characterized by the cluster size. � 2017 Elsevier B.V.