School Of Basic And Applied Sciences
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Item Topological insulator behavior of WS 2 monolayer with square-octagon ring structure(American Institute of Physics Inc., 2016) Kumar, Ashok; Pandey, Ravindra; Ahluwalia, P. K.; Tankeshwar, K.We report electronic behavior of an allotrope of monolayer WS 2 with a square octagon ring structure, refereed to as (so-WS 2 ) within state-of-the-art density functional theory (DFT) calculations. The WS 2 monolayer shows semi-metallic characteristics with Dirac-cone like features around Cyrillic capital letter GHE. Unlike p-orbital's Dirac-cone in graphene, the Dirac-cone in the so-WS 2 monolayer originates from the d-electrons of the W atom in the lattice. Most interestingly, the spin-orbit interaction associated with d-electrons induce a finite band-gap that results into the metal-semiconductor transition and topological insulator-like behavior in the so-WS 2 monolayer. These characteristics suggest the so-WS 2 monolayer to be a promising candidate for the next-generation electronic and spintronics devices.Item Monolayer, Bilayer, and Heterostructures of Green Phosphorene for Water Splitting and Photovoltaics(American Chemical Society, 2018) Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.; Pandey, RavindraWe report the results of density functional theory-based calculations on monolayer and bilayer green phosphorene and their heterostructures with MoSe 2 . Both monolayer and bilayer green phosphorene are direct band gap semiconductors and possess anisotropic carrier mobility as high as 10 4 cm 2 /V/s. In bilayers, the pressure of about 9 GPa induces the semiconductor-metal transition. Moreover, the band gap depends strongly on the thickness of the films and the external electric field. By employing strain engineering under suitable solution conditions, monolayer and AC-stacked bilayer green phosphorene offer the band edge alignments which can be used for water splitting. The upper limit of the power conversion efficiencies for monolayer and AB- and AC-stacked bilayer green phosphorene heterostructures with MoSe 2 is calculated to be 18-21%. Our results show the possibility of green phosphorene to be used as a photocatalytic and photovoltaic material in energy-related applications. - 2018 American Chemical Society.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 Energetics and Electronic Properties of Pt Wires of Different Topologies on Monolayer MoSe 2(AIP Publishing, 2016) Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.The energetics and electronic properties of different of Pt wires including linear, zigzag and ladder structures on MoSe2 have been investigated in the framework of The predicted order of stability of Pt wire on MoSe2 is found to be: linear > ladder > zigzag. Pt wires induce states near the of MoSe2 that results into metallic characteristics of Pt-wire/MoSe2 assembled system. signifies most of the contribution from Pt atoms near the Fermi energy of assembled wire/MoSe2 system. These findings are expected to be important for the of based on MoSe2 layers for flexible nanoelectronics.Item Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group- V Elements(Institute of Physics (IOP), 2017) Jamdagni, Pooja; Kumar, Ashok; Thakur, Anil; Pandey, Ravindra; Ahluwalia, P. K.Topological defects in ultrathin layers are often formed during synthesis and processing, thereby, strongly influencing the electronic properties of the layered systems. For the monolayers of Sn and group-V elements, we report the results based on density functional theory determining the role of Stone-Wales (SW) defects in modifying their electronic properties. The calculated results find the electronic properties of Sn monolayer to be strongly dependent on the concentration of SW-defects e.g., defective stanene has nearly zero band gap (≈ 0.03 eV) for the defect concentration of 2.2 x 10<sup>13</sup> cm<sup>-2</sup> which opens up to 0.2 eV for the defect concentration of 3.7 x 10<sup>13</sup> cm<sup>-2</sup>. In contrast, SW-defects appear to induce conduction states in the semiconducting monolayers of group-V elements. These conduction states act as channels for electron tunnelling, and the calculated tunnelling characteristics show the highest differential conductance for the negative bias with the asymmetric current-voltage characteristics. On the other hand, the highest differential conductance was found for the positive bias in stanene. Simulated STM topographical images of stanene and group-V monolayers show distinctly different features in terms of their cross-sectional views and distance-height profiles. These distinctive features can serve as fingerprints to identify the topological defects in experiments for the monolayers of group-IV and group-V elements.