Browsing by Author "Kumar, Jagdish"

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    Alloyed monolayers of Cu, Ag, Au and Pt in hexagonal phase: A comprehensive first principles study
    (Elsevier Ltd, 2018) Kapoor, Pooja; Kumar, Arun; Sharma, Munish; Kumar, Jagdish; Kumar, Ashok; Ahluwalia, P. K.
    We present density functional theory (DFT) based comprehensive study of two-dimensional (2D) alloyed monolayers of noble metals (AgCu, AgPt, AgAu, AuCu, AuPt and CuPt) in hexagonal phase within numerical atomic orbitals and plane wave basis sets methods. The monolayers considered exhibit positive phonon frequencies suggesting them to be dynamically stable. The Pt containing alloyed monolayers have superior structural stability (binding energy and tensile strength) and exhibit metallic and ferromagnetic character amongst all the alloyed monolayers. Interestingly, alloying of Au monolayer with Cu and Ag show semiconducting behavior whereas alloyed AgCu monolayer posseses Dirac-cone like features at high symmetry points. These distinct features in electronic structures of alloyed 2D monolayers have been captured in STM like set up. An anisotropic behavior has been observed in dielectric spectra for all the considered structures. Tunneling characteristics show NDR region for Pt containing alloyed monolayers. The considered alloyed monolayers may potentially be useful as a building blocks for the applications in nano- and opto-electronics. ? 2017 Elsevier B.V.
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    Electronic and optical properties of boron-based hybrid monolayers
    (IOP Publishing Ltd, 2021-06-24T00:00:00) Katoch, Neha; Kumar, Ashok; Kumar, Jagdish; Ahluwalia, P.K.; Pandey, Ravindra
    Anisotropic 2D Dirac cone materials are important for the fabrication of nanodevices having direction-dependent characteristics since the anisotropic Dirac cones lead to different values of Fermi velocities yielding variable carrier concentrations. In this work, the feasibility of the B-based hybrid monolayers BX (X = As, Sb, and Bi), as anisotropic Dirac cone materials is investigated. Calculations based on density functional theory and molecular dynamics method find the stability of these monolayers exhibiting unique electronic properties. For example, the BAs monolayer possesses a robust self-doping feature, whereas the BSb monolayer carries the intrinsic charge carrier concentration of the order of 1012 cm?2 which is comparable to that of graphene. Moreover, the direction-dependent optical response is predicted in these B-based monolayers; a high IR response in the x-direction is accompanied with that in the visible region along the y-direction. The results are, therefore, expected to help in realizing the B-based devices for nanoscale applications. � 2021 IOP Publishing Ltd Printed in the UK
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    Electronic, Mechanical, and Dielectric Properties of Two-Dimensional Atomic Layers of Noble Metals
    (Springer New York LLC, 2017) Kapoor, Pooja; Kumar, Jagdish; Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.
    We present density functional theory-based electronic, mechanical, and dielectric properties of monolayers and bilayers of noble metals (Au, Ag, Cu, and Pt) taken with graphene-like hexagonal structure. The Au, Ag, and Pt bilayers stabilize in AA-stacked configuration, while the Cu bilayer favors the AB stacking pattern. The quantum ballistic conductance of the noble-metal mono- and bilayers is remarkably increased compared with their bulk counterparts. Among the studied systems, the tensile strength is found to be highest for the Pt monolayer and bilayer. The noble metals in mono- and bilayer form show distinctly different electron energy loss spectra and reflectance spectra due to the quantum confinement effect on going from bulk to the monolayer limit. Such tunability of the electronic and dielectric properties of noble metals by reducing the degrees of freedom of electrons offers promise for their use in nanoelectronics and optoelectronics applications. ? 2016, The Minerals, Metals & Materials Society.
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    Optoelectronic and photocatalytic properties of stable pentagonal B2S and B2Se monolayers
    (Elsevier B.V., 2022-06-01T00:00:00) Katoch, Neha; Kumar, Jagdish; Kumar, Ashok; Ahluwalia, P.K.; Pandey, Ravindra
    Boron-based 2D monolayers have attracted tremendous interest due to their unique physical and chemical properties. In this paper, we report novel pentagonal monolayers, B2S and B2Se, which are predicted to be energetically, dynamically, and thermally stable based on density functional theory. At the HSE06 level of theory, they exhibit a moderate indirect bandgap of (e.g., 1.82 eV for Penta-B2S and 1.94 eV for Penta-B2Se). Strain-induced indirect-to-direct bandgap transition, high hole mobility (~103 Cm2V-1S-1) and strong optical absorption (? ~105 Cm-1) in the visible region are observed for these monolayers. Moreover, the electronic band structures and optical spectra are tunable by mechanical strains suggesting their visible light-harvesting capabilities for optoelectronic applications. In this way, the pentagonal family of 2D materials is now expanded to include boron-containing photocatalytic materials for water splitting applications. � 2022
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    Spin-polarized linear dispersions, lattice dynamics and transport properties of quaternary Heusler alloys (LiMgXSb)
    (Elsevier Ltd, 2023-01-16T00:00:00) Nag, Abhinav; Gupta, Yuhit; Kumar, Jagdish
    In this study, we are predicting a new class of materials obtained by substituting a magnetic transition metal ion in quaternary Heusler alloys with the formula LiMgXSb (X = Co, Cr, Fe, Mn). We found that all the studied alloys exhibit a ferromagnetic ground state except LiMgCoSb. The phonon dispersions of the studied alloys computed within spin-polarized density functional perturbation theory (DFPT) do not exhibit any imaginary frequencies indicating that the proposed alloys are dynamically stable. The band structure calculations show that the studied alloys are metallic and exhibit the states near Fermi level for both spins. The fixed spin moment (FSM) calculations have been employed to exclude the possibility of other ferromagnetic ground states. One of the most interesting aspects of the band structure of these compounds is the existence of multiple band crossings leading to multiple Weyl points in the Brillouin zone. We have also computed the spin-polarized transport properties of these alloys. Our results find that doping charge carriers in the unit cell can significantly enhance the power factor and ZT. Electron doping is more effective for improving the power factor. Our findings show that among all the alloys LiMgFeSb has the highest ZT value with electron doping. Our studied materials constitute a new family of three-dimensional materials exhibiting band degeneracies that lead to Weyl points. � 2023 Elsevier B.V.