Browsing by Author "Tankeshwar, K."

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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).
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).
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.
Electronic properties of ultrathin 2D and 1D alloyed nanostructures of stanene
(American Institute of Physics Inc., 2017) Sachdeva, Geeta; Kumar, Chandra; Tankeshwar, K.; Kumar, Ashok
Electronic 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).
Electronic structure and simulated STM images of non-honeycomb phosphorene allotropes
(American Institute of Physics Inc., 2018) Kaur, S.; Kumar, A.; Srivastava, S.; Tankeshwar, K.
We have investigated the electronic structure and simulated STM images of various non-honeycomb allotropes of phosphorene namely ? - P, ? - P, ? - P and ? - P, within combined density functional theory and Tersoff-Hamman approach. All these allotropes are found to be energetically stable and electronically semiconductingwith bandgap ranging between 0.5-1.2 eV. Simulated STM images show distinctly different features in terms of the topography. Different maximas in the distance-height profile indicates the difference in buckling of atoms in these allotropes. Distinctly different images obtained in this study may be useful to differentiate various allotropes that can serve as fingerprints to identify various allotropes during the synthesis of phosphorene. ? 2018 Author(s).
Electronic structure engineering of various structural phases of phosphorene
(Royal Society of Chemistry, 2016) Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.
We report the tailoring of the electronic structures of various structural phases of phosphorene (?-P, ?-P, ?-P and ?-P) based homo- and hetero-bilayers through in-plane mechanical strains, vertical pressure and transverse electric field by employing density functional theory. In-plane biaxial strains have considerably modified the electronic bandgap of both homo- and hetero-bilayers while vertical pressure induces metallization in the considered structures. The ?-P homo-bilayer structure showed the highest ultimate tensile strength (UTS ? 6.21 GPa) upon in-plane stretching. Upon application of a transverse electric field, the variation in the bandgap of hetero-bilayers was found to be strongly dependent on the polarity of the applied field which is attributed to the counterbalance between the external electric field and the internal field induced by different structural phases and heterogeneity in the arrangements of atoms of each surface of the hetero-bilayer system. Our results demonstrate that the electronic structures of the considered hetero- and homo-bilayers of phosphorene could be modified by biaxial strain, pressure and electric field to achieve the desired properties for future nano-electronic devices. ? the Owner Societies 2016.
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).
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, Ravindra
We 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.
Photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers
(Royal Society of Chemistry, 2022-09-01T00:00:00) Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.
The highly efficient photocatalytic water splitting process to produce clean energy requires novel semiconductor materials to achieve a high solar-to-hydrogen energy conversion efficiency. Herein, the photocatalytic properties of anisotropic ?-PtX2 (X = S, Se) and Janus ?-PtSSe monolayers were investigated based on the density functional theory. The small cleavage energy for ?-PtS2 (0.44 J m?2) and ?-PtSe2 (0.40 J m?2) endorses the possibility of mechanical exfoliation from their respective layered bulk materials. The calculated results revealed that the ?-PtX2 monolayers have an appropriate bandgap (?1.8-2.6 eV) enclosing the water redox potential, light absorption coefficient (?104 cm?1), and exciton binding energy (?0.5-0.7 eV), which facilitates excellent visible-light-driven photocatalytic performance. Remarkably, the inherent structural anisotropy leads to an anisotropic high carrier mobility (up to ?5 � 103 cm2 V?1 S?1), leading to a fast transport of photogenerated carriers. Notably, the required small external potential to realize hydrogen evolution reaction and oxygen evolution reaction processes with an excellent solar-to-hydrogen energy conversion efficiency for ?-PtSe2 (?16%) and ?-PtSSe (?18%) makes them promising candidates for solar water splitting applications. � 2022 The Royal Society of Chemistry.
Pressure and electric field tuning of Schottky contacts in PdSe2/ZT-MoSe2 van der Waals heterostructure
(Institute of Physics Publishing, 2020) Jakhar, M; Singh, J; Kumar, A; Tankeshwar, K.
A two-dimensional van der Waals (vdW) heterostructure (PdSe2/ZT-MoSe2) has been investigated through vdW corrected density functional theory. ZT-MoSe2 acts as a Dirac material with an anisotropic Dirac cone and variable Fermi velocity (0.52-1.91 105 ms-1). The intrinsic Schottky barrier height can be effectively tuned by applying external pressure and an electric field to the heterostructure. The p-type Schottky barrier transforms into a p-type ohmic contact at pressure P ? 16 GPa. A positive electric field induces p-type ohmic contact while a negative electric field results in the transition from p-type Schottky contact to n-type Schottky contact, and finally to n-type ohmic contact at the higher values of the field. Moreover, the external positive (negative) electric field induces n-type (p-type) doping of ZT-MoSe2 in the heterostructure and remarkably controls the charge carrier concentration. Our results demonstrate that controlling the external pressure and electric field in a PdSe2/ZT-MoSe2 heterostructure can result in an unprecedented opportunity for the design of high-performance nanodevices. � 2020 IOP Publishing Ltd.
Recent advances in 2D anode materials for Na-ion batteries from a theoretical perspective
(Taylor and Francis Ltd., 2023-11-02T00:00:00) Verma, Nidhi; Jamdagni, Pooja; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.
Na-ion batteries (SIBs) are a promising replacement for lithium-ion batteries (LIBs) for low-cost and large-scale energy storage systems in the forthcoming years after additional in-depth examination and investigation. A significant part of the development of innovative anode materials and their in-depth understanding has come through simulations. Ab initio simulations based on density functional theory (DFT) have been proven to be a reliable, efficient, and cost-effective way to design new anode materials for SIBs. As a result of the identification of graphene, researchers and scientists were influenced to create new two-dimensional (2D) materials. On account of their distinctive physical and chemical properties, the broad expanse of surface, innovative electronic features, and charging ability of 2D materials attract much attention. Many of these characteristics are significant prerequisites for using anodes in batteries. Herein, based on recent research progress, we have reviewed the structures and electrochemical properties of 2D materials as anode for Na-ion batteries from a theoretical perspective. The effective methodologies for high-performance anode materials are provided based on the substantial literature and theoretical studies. Added to that, we have also explored the various techniques such as heterostructure, doping, defect- and strain-engineering of 2D materials for the improvement of the performance of these materials as anodes for SIBs. � 2023 Taylor & Francis Group, LLC.
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.
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).
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.
Ultra-narrow blue phosphorene nanoribbons for tunable optoelectronics
(Royal Society of Chemistry, 2017) Swaroop, Ram; Ahluwalia, P. K.; Tankeshwar, K.; Kumar, Ashok
We report optoelectronic properties of ultra-narrow blue phosphorene nanoribbons (BPNRs) within the state-of-the-art density functional theory framework. The positive but small value of formation energy (?0.1 eV per atom) indicates the relative ease of the formation of BPNRs from their two-dimensional (2D) counterpart. The oscillatory behaviour of the electronic band gap of bare BPNRs with increasing width is attributed to the reconstruction of edge atoms. The static dielectric constant of BPNRs depends on the width and applied strain which in turn shows consistency with the Penn's model expression for semiconductors. Bare BPNRs exhibit both ? and ? + ? plasmonic structures while passivated ones possess only a ? + ? plasmonic structure that get blue-shifted (as large as ?3 eV) on increasing the width of the BPNRs which makes electron energy loss spectroscopy useful for identifying the width of BPNRs in real experimental situations. The mechanical strain induces a small red shift in, which is attributed to the modification in electronic band dispersion due to a different superposition of atomic orbitals on the application of applied strain. These tunable electronic and dielectric properties of BPNRs mean they may find applications in optoelectronic devices based on blue phosphorene. ? The Royal Society of Chemistry.
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.