Department of Physics

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IIT Jodhpur

Two-dimensional layered transition metal dichalcogenide exhibit important characteristics such as suitable bandgap, high absorption coefficient, and favourable electron transport properties for their uses in nano-electronic such as ultrathin solar cells. We adopted a hybrid simulation approach, where density functional calculations are performed for optoelectronic properties of semiconductor materials and macroscopic device simulation is carried out to evaluate photovoltaic response. We investigated electronic and optical properties of bulk WS2, WSe2 and noticed very high absorption coefficient, making them suitable absorber materials for solar cell. Further, the electronic and optical properties of an ultrathin WSSe Janus layer are investigated using density functional theory and noticed low reflectance and high bandgap, supporting its usefulness as a buffer layer for W(S/Se)2 absorbers. The computed density functional results for W(S/Se)2 and Janus WSSe are used to simulate the photovoltaic response of WSSe/W(S/Se)2 solar cell using macroscopic device simulation. The photovoltaic performance of a single junction solar cell is optimized for W(S/Se)2 absorbers and WSSe Janus buffer materials. The effect of absorber layer thickness, carrier concentration, and contact work function is evaluated to understand the solar cell performance. We noticed that interface recombination speed between absorber and buffer layer and minority carrier lifetime are affecting the solar cell performance. The maximum efficiency of about ~17.73% and 18.87% is noticed for optimized WSSe/WS2 and WSSe/WSe2 solar cell. The present study will provide a new approach to design, develop, and optimize a solar cell and evaluate the impact of different materials parameters on solar cell performance. © 2019 Elsevier B.V.

World University root node

Solar Energy Materials and Solar Cells

Ultrathin Janus WSSe buffer layer for W(S/Se)2 absorber based solar cells: A hybrid, DFT and macroscopic, simulation studies

Abstract: The capacity retention of lithium intercalated cathode materials is strongly dependent on their surface condition, if surface is modified with various solid state compounds. In the present work one representative of carbosilicide type compounds known in literature as MAX-phase group (M n+1 AX n , where M is a transition metal, A is an element of III–VI group, and X is C and/or N) was used as surface modification agent. Synthesis temperature of Ti 3 SiC 2 (TSC) compound, which is close to 1500 °C, was decreased by the application of special treatment of the reagents blend. The mechanism acting of TSC modification is presented and compared with other models, suggested in literature. Based on the results of experiments with different TSC contents and different substrate types we found positive effect of surface modification with TSC of the phosphate-based lithium intercalated cathode materials on their capacity fading rate. Outstanding high electronic conductivity of TSC makes this phase applicable as co-component in the composite electrode materials. Graphical abstract: [Figure not available: see fulltext.]. © 2018, Springer-Verlag GmbH Austria, part of Springer Nature.

Monatshefte fur Chemie

Positive effect of surface modification with titanium carbosilicide on performance of lithium-transition metal phosphate cathode materials

We explore the possibility of simultaneous explanation of RK(*) and RD(*) measurements in a model dependent approach. We reanalysed the four new physics models: Standard model like vector boson (VB), SU(2)L-singlet vector leptoquark (U1), SU(2)L-triplet scalar leptoquark (S3) and SU(2)L triplet vector leptoquark (U3) models. The new physics couplings are assumed only to the third generation in the weak basis. We found that vector boson model is not consistent with the present data as the branching ratio of B(τ → 3μ) evades the upper bound on the best fit point. The three leptoquark models cannot simultaneously accomodate the RK (*) and RD(*) measurements. © Springer Nature Switzerland AG 2019.

Springer Proceedings in Physics

Simultaneous Explanation of RK(*) and RD(*) in Various New Physics Models

We synthesized Hg alloyed CdTe quantum dots (Cd1−xHgxTe) using hydrothermal route. N-acetyl-cysteine is used as the capping agent for water dispersed Cd1−xHgxTe (x = 0, 0.05, 0.1 and 0.5) quantum dots. The diameter of the synthesized quantum dots is 3.8 ± 0.5 nm, as estimated from high resolution transmission electron micrographs. The mercury molar fraction modified band gap engineering is demonstrated with band gap changing from 2.5 eV for CdTe quantum dots to 1.25 eV for Cd0.5Hg0.5Te. © Springer Nature Switzerland AG 2019.

Band gap engineering of cdte quantum dots by hg alloying in infrared region

This work is at the interface of graph theory and quantum mechanics. Quantum correlations epitomize the usefulness of quantum mechanics. Quantum discord is an interesting facet of bipartite quantum correlations. Earlier, it was shown that every combinatorial graph corresponds to quantum states whose characteristics are reflected in the structure of the underlined graph. A number of combinatorial relations between quantum discord and simple graphs were studied. To extend the scope of these studies, we need to generalize the earlier concepts applicable to simple graphs to weighted graphs, corresponding to a diverse class of quantum states. To this effect, we determine the class of quantum states whose density matrix representation can be derived from graph Laplacian matrices associated with a weighted directed graph and call them graph Laplacian quantum states. We find the graph theoretic conditions for zero and nonzero quantum discord for these states. We apply these results on some important pure two qubit states, as well as a number of mixed quantum states, such as the Werner, Isotropic, and X-states. We also consider graph Laplacian states corresponding to simple graphs as a special case. © 2019 World Scientific Publishing Company.

Fulltext

International Journal of Quantum Information

Condition for zero and nonzero discord in graph Laplacian quantum states

We investigated the impact of residual oxygen on thermal emittance of tungsten on stainless steel (W/SS) in conjunction with its intrinsic absorbing properties. The optimal emittance value is limited to ∼0.13 for the least oxygen contaminated tungsten thin films and ∼0.2 thermal emittance with small residual oxygen. In addition, the synthesized tungsten structures also exhibit significant solar absorption ∼0.76 and 0.78 for the least oxygen contaminated and small oxygen contaminated tungsten thin films. The relatively large value of thermal emittance is attributed to the intrinsic interband transition in infrared region. The observed relatively large absorption for both structures in 0.2-0.9 μm wavelength range is attributed the residual oxygen, which resulted in the formation of WOx, causing the cermet structure. The results suggest that the best emittance ∼0.13 can be achieved provided oxygen contamination can be avoided while synthesizing the tungsten thin films for infrared reflector applications in spectrally selective coating structures. This is also attributed partially to the intrinsic interband absorption in tungsten metal. © 2019 IOP Publishing Ltd.

Materials Research Express

W/SS thin film as high temperature infrared reflector for solar thermal applications: Intrinsic properties and impact of residual oxygen

This book examines the application of nanoscience and nanotechnology in military defence strategies. Both historical and current perspectives on military technologies are discussed. The book provides comprehensive details on current trends in the application of nanotechnology to ground, air, and naval specializations. Furthermore, nanotechnology-enabled high energy explosives and propellants, chemical, biological, radiation, and nuclear threats and their detection/protection, and camouflage and stealth for signature management of military targets in multispectral wavelength signals are analyzed. The book also covers nanotechnology-enabled armor and platforms, which may serve as lightweight and high mechanical strength options in contrast to conventional systems. Finally, the book also emphasizes future military applications of nanotechnology and its integration into ‘smart’ materials. Provides comprehensive details on trends in the application of nanotechnology to ground, air, and naval defence systems; Examines the application of nanoscience and nanotechnology in military defence strategies; Offers pathways and research avenues for development of nanotechnology and materials applications in military capacities. © Springer Nature Switzerland AG 2019.

Nanotechnology for Defence Applications

Nanotechnology for defence applications

Combined kinetic theory-hydrodynamics treatment has been proven effective in the prediction of biomolecule dynamics, generally if a single biomolecule is present in the bulk solvent. But the validity of such a theory in many physiological conditions is controversial. In the present study, a sample protein surrounded by other large biomolecules is approximated as the protein in a cylindrical nanopore. The hydrodynamic radius of the protein is chosen as an indicator to check whether one of the widely used kinetic theoryhydrodynamics relation namely Stokes-Einstein-Debye relation, is genuine for confined conditions of the protein. It has been found that Stokes-Einstein-Debye relation cannot be satisfied by the protein if confinement dimensions are very close. The reason for the violation can be attributed to van der Waals interaction between pore and the protein. © 2019, Avestia Publishing.

Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering

Stokes-einstein-debye relation: A check of validity for proteins in nanoconfinement

Rapidly quenched Co- and Fe-based monolayer and their bilayer prepared through double nozzle technique have been characterized to investigate its microstructural and magnetic properties and their possibility as high-temperature magnetocaloric material. The Co- and Fe-based monolayer ribbons displayed Curie temperatures (TC) of 463 K and 700 K, respectively. Magnetic entropy change ∆SM of the bilayer was measured at a low magnetizing field of 1 T in the temperature spans covering separately for TC of Co- and Fe-based ribbons corresponding to separate entropy at low- and high-temperature regime. The ∆SM value at TC of Fe-based ribbon displayed values in the span of 1.13–1.71 J kg−1 K−1 in their monolayer and bilayer state. On incipient nanocrystallisation at 773 K, the ∆SM and refrigerant capacity (RC) around TC of cobalt-based bilayer ribbon revealed comparable values as in their as-quenched state. However, nanocrystallisation elevated the ∆SM of bilayer across TC of the Fe-based regime to a high value close to 4.6 J kg−1 K−1 with a fairly elevated RC of 96 J kg−1. The enhanced ∆SM associated with the formation of Fe-based nanocrystallites is evidenced through transmission electron microscopy. The interdiffusion of ferromagnetic elements Fe and Co is also supposed to elevate the ∆SM as well as the RC of the glassy system in the bilayer ribbons. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Materials Science

High-temperature magnetocaloric effect in devitrified Fe/Co based glassy monolayer and bilayer ribbons

The recovery and recrystallization behaviors of low-carbon interstitial-free steel are investigated at different annealing temperatures (200-690 °C) through correlation between the changes in magnetic parameters (coercivity and r.m.s. voltage), hardness, tensile strength and high-angle grain boundary fractions (HAB). Magnetic parameters and tensile strength show a significant change within recovery region (200-500 °C), while the hardness variation is very minimal at this temperature region. On the other hand, the hardness is abruptly changed compared to magnetic properties at higher annealing temperature (550-640 °C). The grain boundary characteristics and microtexture evolution occurring at recrystallization regime are evaluated by orientation imaging microscopy (OIM) and orientation distribution function (ODF) through electron backscattered diffraction (EBSD). The increase in recrystallization fraction noticeably affects microtexture property, justifying with the strengthening of γ-fiber, weakening of α-fiber and disappearance of rotated cube component with increasing annealing temperatures. © 2019, ASM International.