Department Of Physics
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Item Energetics and electronic structure of novel hybrid dumbbell monolayers(American Institute of Physics, 2019) Kaur, S; Singh, J; Kumar, Ashok; Srivastava, S; Tankeshwar, K.We report three new hybrid monolayers (C6P4, C6N4 and N6P4) of group-IV and group-V elements in dumbbell structure using density functional theory calculations. C6P4, C6N4 possess sp2 as well as sp3 hybridization in their honeycomb dumbbell structure while N6P4 possess only the sp3 hybridization in its non-honeycomb but dumbbell structure. The magnitude of cohesive energy of these hybrid monolayers suggests that C6N4 is the most favorable monolayer to be formed. We found that C6P4 is metallic while C6N4 and N6P4 are semiconductors. Also, we report as a representative case, the systematic structural phase transition from LHD-C to a new phosphorous allotrope which has been suggested to exists in our cohesive energy calculations. The reported monolayers join the family of two dimensional materials and may possess application in nanoelectronic devices. © 2019 Author(s).Item Stability and electronic properties of two dimensional pentagonal layers of palladium chalcogenides(American Institute of Physics, 2019) Kumar, Ashok; Jakhar, M; Srivastava, S; Tankeshwar, K.We report structural and electronic properties of pristine and hybrid monolayers/bilayers of Pd chlcogenides within state-of-the-art density functional theory (DFT) calculations. The calculated cohesive energy suggests hybrid systems to be more stable than pristine monolayer/bilayer system. The considered structures show indirect band gap which get reduced on going from monolayer to bilayers. Spin-orbit coupling (SOC) further reduce the bandgap by shifting the band edges towards Fermi level. The reduction in band gap of hybrid bilayers is more pronounced which is attributed to the electronegativity difference between chalcogen S/Se atoms and greater charge redistribution between the layers. We believe that our theoretical study will add more 2D materials in the fascinating class of new 2D family and may guide the experimentalists to realize them for various future nano-electronic applications. © 2019 Author(s).Item Adsorption of nucleobases on different allotropes of phosphorene(American Institute of Physics, 2019) Jakhar, M; Kumar, Ashok; Srivastava, S; Parida, P; Tankeshwar, K.There has been tremendous interest in low-dimensional quantum systems during past two decades, fueled by a constant stream of striking discoveries and also by the potential for, and realization of, new state-of-the-art electronic device architectures. In this paper, our work includes the structural, electronic and optical properties of nucleobase (Adenine(A), Cytosine(C), Guanine(G), Thymine(T)) adsorbed on different allotropes of phosphorene (α, β, γ). From the optical absorption spectra of different nucleobases when adsorbed on the surface of phosphorene, we could optically probe different Nucleobases. As phosphorene shows different spectra for different nucleobases, it behaves as a bio-sensor to detect various nucleobases. © 2019 Author(s).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 Van der Waals heterostructures based on allotropes of phosphorene and MoSe2(Royal Society of Chemistry, 2017) Kaur, Sumandeep; Kumar,Ashok; Srivastava, Sunita; Tankeshwar, K.The van der Waals heterostructures of allotropes of phosphorene (?- and ?-P) with MoSe2 (H-, T-, ZT- and SO-MoSe2) are investigated in the framework of state-of-the-art density functional theory. The semiconducting heterostructures, ?-P/H-MoSe2 and ?-P/H-MoSe2, form anti-type structures with type I and type II band alignments, respectively, whose bands are tunable with an external electric field. ?-P/ZT-MoSe2 and ?-P/SO-MoSe2 form ohmic semiconductor-metal contacts while the Schottky barrier in ?-P/T-MoSe2 can be reduced to zero by an external electric field to form ohmic contacts which is useful to realize high-performance devices. Simulated STM images of the given heterostructures reveal that ?-P can be used as a capping layer to differentiate between various allotropes of underlying MoSe2. The dielectric response of the considered heterostructures is highly anisotropic in terms of lateral and vertical polarization. The tunable electronic and dielectric response of van der Waals phosphorene/MoSe2 heterostructures may find potential applications in the fabrication of optoelectronic devices. ? 2017 the Owner Societies.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 Electronic Properties of Phosphorene/MoSe 2 Vertical Hetero-structures(AIP Publishing, 2017) Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.We report three structurally different and stable phases of MoSe2 namely h-MoSe2 (trigonal prismatic phase), t-MoSe2 (distorted octahedral coordinated phase) and o-MoSe2 (consisting of repeated octagon pairs) and their hetero-structures with black phosphorene. The MoSe2-octa phase possesses graphene-like character i.e. cone feature at the All the considered hetero-structures are energetically equally favorable. The h-MoSe2/black-P is found to be a in nature while on the other hand t-MoSe2/black-P and o-MoSe2black-P are metallic. These novel hetero-structures may be useful in the of nano-electronic based on phosphorene hetero-structures.Item Electronic properties of ultrathin 2D and 1D alloyed nanostructures of stanene(American Institute of Physics Inc., 2017) Sachdeva, Geeta; Kumar, Chandra; Tankeshwar, K.; Kumar, AshokElectronic structure of two dimensional (2D) and one dimensional (1D) ultrathin alloyed nanostructures of stanene has been investigated within the framework of state-of-the-art density functional theory (DFT). Ultrathin stanene is Dirac semimetal with linear dispersion of bands at K-point, whereas ?0.2 eV energy gap get induced in alloyed stanene, thereby, offers wide variety of application at nanoscale. Furthermore, the mechanical strength of alloyed stanene increases from 1.6 GPa in pristine monolayer to 2.2 GPa in alloyed nanostructure. Various topologies of 1D nanostructures are found to metallic in nature with calculated ballistic conductance in the range 2G0 to 4 G0. Our theoretical predictions may be useful for experimentalist to fabricate devices based on ultrathin nanostructures of alloyed stanene. ? 2017 Author(s).Item Electronic properties of phosphorene/graphene heterostructures: Effect of external electric field(American Institute of Physics Inc., 2016) Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.We report the electronic properties of electrically gated heterostructures of black and blue phosphorene with graphene. The heterostructure of blue phosphorene with graphene is energetically more favorable than black phospherene/graphene. However, both are bonded by weak interlayer interactions. Graphene induces the Dirac cone character in both heterostructure which shows tunabilities with external electric field. It is found that Dirac cone get shifted depending on the polarity of external electric field that results into the so called self induced p-type or n-type doping effect. These features have importance in the fabrication of nano-electronic devices based on the phosphorene/graphene heterostructures. ? 2016 Author(s).