Department Of Physics
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Item Twisted helical armchair graphene nanoribbons: mechanical and electronic properties(Springer Science and Business Media Deutschland GmbH, 2021-05-08T00:00:00) Thakur, Rajesh; Ahluwalia, P.K.; Kumar, Ashok; Sharma, Munish; Sharma, RamanAbstract: The Hydrogen and Fluorine planar armchairs graphene nanoribbons (H & F AGNRs), subjected to twist deformation within fixed periodic boundary conditions. H-AGNRs is highly elastic in nature, though passivation with Fluorine does induce the plasticity when twisted beyond threshold torsional strain. This plasticity attributes to the wider bond length distribution suggests distortion of benzo-rings. The bandgap response to the effective strain of narrow GNRs N= 6 , 7 , and 8 get arranged as (i) monotonously increasing for q= 0 , 2 and (ii) decreasing for q= 1 ; here, q= mod(N, 3) in effective strain space (?2?2). The effective strain space is found to be more appropriate for gauging the response of torsional strain. This trend has also been observed for Fluorine passivated AGNRs; however, because of higher sensitive response to torsional strain, the bandgap of N= 7 F-AGNRs drops from Eg? 0.95 eV to Eg? 0.05 eV at extreme torsional strain forming Dirac cone at � K allows dissipationless transport to charge carriers of high kinetic energy at low bias. Graphic abstract: [Figure not available: see fulltext.] � 2021, The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature.Item Stability and electronic properties of bilayer graphene spirals(Elsevier B.V., 2021-01-19T00:00:00) Thakur, Rajesh; Ahluwalia, P.K.; Kumar, Ashok; Sharma, RamanSpiral topology offers many potential applications to next-generation nanoelectronic devices. The ab-initio simulations are used to investigate the stability and electronic properties of the hexagonal and triangular double-layer spiral (DLS). A room temperature molecular dynamics (MD) simulation reveals that the AA stacking of triangular DLS (t-DLS) is thermodynamically stable, however, the AA stacking of hexagonal DLS (h-DLS)is found to get distorted. When h-DLS and t-DLS are subjected to tensile strain the h-DLS behaved elastically, however, the t-DLS is extremely brittle. Both h-DLS and t-DLS are observed to be metallic in an equilibrium state. On applying an electric field, the h-DLS remains metallic, whereas, the t-DLS becomes a semiconductor. The bandgap of t-DLS is observed to open up even for a small magnitude of electric field. Furthermore, we also found that the triangular-shaped bilayer spiral topology gives rise to an intrinsic Rashba splitting. Our study opens up new and innovative ideas for investigating the spiral-shaped nano-structures. � 2021 Elsevier B.V.Item Stability and carrier transport properties of phosphorene-based polymorphic nanoribbons(Institute of Physics Publishing, 2018) Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.Few-layer black phosphorene has recently attracted significant interest in the scientific community. In this paper, we consider several polymorphs of phosphorene nanoribbons (PNRs) and employ deformation potential theory within the effective mass approximation, together with density functional theory, to investigate their structural, mechanical and electronic properties. The results show that the stability of a PNR strongly depends on the direction along which it can be cut from its 2D counterpart. PNRs also exhibit a wide range of line stiffnesses ranging from 6 ?1010 eV m-1 to 18 ?1011 eV m-1, which has little dependence on the edge passivation. Likewise, the calculated electronic properties of PNRs show them to be either a narrow-gap semiconductor (E g < 1 eV) or a wide-gap semiconductor (E g > 1 eV). The carrier mobility of PNRs is found to be comparable to that of black phosphorene. Some of the PNRs show an n-type (p-type) semiconducting character owing to their higher electron (hole) mobility. Passivation of the edges leads to n-type ? p-type transition in many of the PNRs considered. The predicted novel characteristics of PNRs, with a wide range of mechanical and electronic properties, make them potentially suitable for use in nanoscale devices. ? 2018 IOP Publishing Ltd.Item Stability and electronic properties of hybrid SnO bilayers: SnO/graphene and SnO/BN(Institute of Physics Publishing, 2017) Guo, Qing; Wang, Gaoxue; Kumar, Ashok; Pandey, RavindraVan der Waals structures based on two-dimensional materials have been considered as promising structures for novel nanoscale electronic devices. Two-dimensional SnO films which display intrinsic p-type semiconducting properties were fabricated recently. In this paper, we consider vertically stacked heterostructures consisting of a SnO monolayer with graphene or a BN monolayer to investigate their stability, electronic and transport properties using density functional theory. The calculated results find that the properties of the constituent monolayers are retained in these SnO-based heterostructures, and a p-type Schottky barrier is formed in the SnO/graphene heterostructure. Additionally, the Schottky barrier can be effectively controlled with an external electric field, which is useful characteristic for the van der Waals heterostructure-based electronic devices. In the SnO/BN heterostructure, the electronic properties of SnO are least affected by the insulating monolayer suggesting that the BN monolayer would be an ideal substrate for SnO-based nanoscale devices. ? 2017 IOP Publishing Ltd.Item Interactions of Gas Molecules with Monolayer MoSe 2 : A First Principle Study(AIP Publishing, 2016) Sharma, Munish; Jamdagni, Pooja; Kumar, Ashok; Ahluwalia, P. K.We present a first principle study of interaction of toxic gas molecules (NO, NO2 and SO2) with MoSe2. The predicted order of sensitivity of gas molecule is NO2 > SO2 > NO. strongly influence the electronic behaviour of MoSe2 by inducing in the vicinity of Fermi energy. NO and SO2 is found to induce p-type effect while to metallic transitions occur on NO2 Our findings may guide the experimentalist for sensor based on MoSe2Item Electronic properties and STM images of vacancy clusters and chains in functionalized silicene and germanene(Elsevier B.V., 2017) Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.Electronic properties and STM topographical images of X (=F, H, O) functionalized silicene and germanene have been investigated by introducing various kind of vacancy clusters and chain patterns in monolayers within density functional theory (DFT) framework. The relative ease of formation of vacancy clusters and chain patterns is found to be energetically most favorable in hydrogenated silicene and germanene. F- and H-functionalized silicene and germanene are direct bandgap semiconducting with bandgap ranging between 0.1?1.9?eV, while O-functionalized monolayers are metallic in nature. By introducing various vacancy clusters and chain patterns in both silicene and germanene, the electronic and magnetic properties get modified in significant manner e.g. F- and H-functionalized silicene and germanene with hexagonal and rectangle vacancy clusters are non-magnetic semiconductors with modified bandgap values while pentagonal and triangle vacancy clusters induce metallicity and magnetic character in monolayers; hexagonal vacancy chain patterns induce direct-to-indirect gap transition while zigzag vacancy chain patterns retain direct bandgap nature of monolayers. Calculated STM topographical images show distinctly different characteristics for various type of vacancy clusters and chain patterns which may be used as electronic fingerprints to identify various vacancy patterns in silicene and germanene created during the process of functionalization. ? 2016 Elsevier B.V.Item 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.