Department Of Physics
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Item 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.Item 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.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 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).Item 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.