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 Strain controlled electronic and transport properties of Si-C atomic wire(American Institute of Physics, 2019) Thakur, R; Kumar, Ashok; Ahluwalia, P.K; Sharma, R.An ab-initio Density functional calculations and Non-equilibrium approach have been used to study the effect of positive strain on the equilibrium geometry, electronic structure and transmission function of Si-C bi atomic wire. In the absence of strain, Si-C bi-atomic wire is found to be semi conducting. The equilibrium electronic structure of these nanowires is shown to change drastically on applying strain. The Si-C bi-atomic wire has wide zigzag (WZ) structure GM and has a direct band gap of 0.7eV and remains direct on applying small strain up to ϵ ∼3.1%. At the strain value of ϵ ∼3.1% the band gap widen up to 1.77eV, and becomes indirect on further increasing the strain values. We observed that at the lower bias the conductance does depend on the strain applied on the wire. From density of states we have found that the strain value of ϵ ∼3.1% offers maximum band gap value up to the ∼1.55eV bias applied. At equilibrium state the transmission through Si bands is observed slightly more, and indicates the holes tunneling through device. Application of strain provides channels for electrons tunneling. © 2019 Author(s).Item Stability, electronic and optical properties of in-plane WSe2 heterophase nano-ribbons(American Institute of Physics, 2019) Bharti, A; Katoch, N; Kumar, Ashok; Sharma, R; Ahluwalia, P.K.We present first principle investigations on in-plane phase engineered nanoribbons with two different widths. 2H and 1T' phases of WSe2 are joined along x-direction, which forms an armchair type interface. The low values of formation energy shows that these structure are energetically stable. The study of electronic structure reveals that they are metallic and the electronic conductivity varies significantly with ribbon length. The ribbons show anisotropic dielectric response compared to constituent monolayers. Optical properties alter considerably for these hetero-systems showing potential for tunable opto-electronic applications. © 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 Tuning of Schottky barriers in borophene/MoS2 van der Waals heterostructure by external electric field(American Institute of Physics, 2019) Katoch, N; Thakur, R; Kumar, Ashok; Ahluwalia, P.K; Kumar, J.A first principle study of structural properties, band bending and tuning of schottky barrier height (SBH) of borophene/MoS2 Van der Waals heterostructure has been carried out within the framework of density functional theory (DFT). Studied binding energy shows that the interaction between borophene and MoS2 is weak. Consequently, both borophene and MoS2 are preserving their electronic nature in heterostructure. We have calculated the band bending 0.15 eV for borophene and -0.52 eV for MoS2 in borophene/MoS2 heterostructure which shows that the metal-semiconductor contact is in between p-type borophene and n-type MoS2. On the application of external electric field, tuning of schottky barriers has been achieved and metal-semiconductor contact gets transformed into ohmic contact which is important for the fast performance of electronic devices. © 2019 Author(s).Item Stability and tunable electronic structure of planar phosphorus nanotubes(American Institute of Physics, 2019) Singh, S; Kaur, S; Gupta, S.K; Kumar, Ashok; Srivastava, S.The stability and electronic properties of planar phosphorous nanotubes with different chirality are investigated within the formulation of density functional theory. Armchair phosphorous nanotube (APNT) is found to be energetically most favorable with very small formation energy (0.08 eV). APNT also possess highest tensile strength (∼2 GPa), among the considered nanotubes. Armchair and helical PNTs are semiconducting while zigzag PNT is metallic in nature. We found that the application of strain and external electric field greatly modifies the electronic band structure of given PNTs. We believe that planar APNT can be realized and its tunable electronic properties may be useful for nanoelectronics. © 2019 Author(s).Item Highly infrared sensitive VO 2 nanowires for a nano-optical device(Royal Society of Chemistry, 2018) Bhuyan, Prabal Dev; Gupta, Sanjeev K; Kumar, Ashok; Sonvane, Yogesh; Gajjar, P. N.Recent studies on the electronic, magnetic and optical properties of VO2 (vanadium dioxide) materials have motivated the exploration of one dimensional VO2 nanowires. First principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of the monoclinic (M) and rutile (R) phases of VO2nanowires. The monoclinic phase shows semiconducting behaviour with a band gap of 1.17 eV, whereas the rutile phase of VO2 nanowires behaves as a spin gapless semiconducting material, as band lines cross the Fermi level due only to up spin contribution. The monoclinic structure of VO2 nanowires is found to be paramagnetic and the rutile structure shows ferromagnetic half metal behavior. The conductivity calculation for VO2 nanowires shows the metal–insulator transition (MIT) temperature to be 250 K. The possible mechanism of VO2 nanowires to be used as smart windows has been discussed, as the nanowires are highly sensitive in the infrared (IR) region. Interestingly, at low temperature, the VO2 monoclinic structure allows infrared light to be transmitted, while VO2 with the rutile phase blocks light in the IR region. Furthermore, we adsorbed CO2, N2 and SO2 gas molecules on 1D VO2 monoclinic nanowire to investigate their interaction behaviour. It was observed that the absorption and transmission properties of VO2 dramatically change upon the adsorption of CO2 and SO2 gas molecules, which is likely to open up its application as an optical gas sensorItem 2D layered transition metal dichalcogenides (MoS2): Synthesis, applications and theoretical aspects(Elsevier, 2018) Singh, Arun Kumar; Kumar, P.; Late, D.J.; Kumar, Ashok; Patel, S.; Singh, JaiRecently, graphene and other two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been widely explored due to their unique optical, mechanical, electrical and sensing properties for versatile electronic and optoelectronic applications. The atomically thin layers of TMDC materials have shown potential to replace state-of-the-art silicon-based technology. Graphene has already revealed an excess of new physics and multifaceted applications in several areas. Similarly, mono-layers of TMDCs such as molybdenum disulfide (MoS2) have also shown excellent electrical and optical properties possessing a direct band-gap of ∼1.8 eV combined with high mechanical flexibility. In contrast to semi-metallic graphene, the semiconducting behavior of MoS2 allows it to overcome the deficiencies of zero-band-gap graphene. This review summarizes the synthesis of 2D MoS2 by several techniques, i.e., mechanical and chemical exfoliation, RF-sputtering, atomic layer deposition (ALD) and chemical vapor deposition (CVD), etc. Furthermore, extensive studies based on potential applications of MoS2 such as the sensor, solar cells, field emission and as an efficient catalyst for hydrogen generation has been included. Theoretical aspects combined with the experimental observations to provide more insights on the dielectric, optical and topological behavior of MoS2 was highlighted.Item Electron transport and thermoelectric performance of defected monolayer MoS2(Elsevier, 2019) Sharm, Munish a; Kumar, Ashok; Ahluwalia, P. K.Electronic and thermoelectric properties of a two-dimensional MoS2 monolayer containing atomic defects are investigated using density functional theory. All the atomic defects have been found to exhibit endothermic nature. Electronic structure of MoS2 shows tuneability of band gap with the atomic defects. The MoS2 vacancy in pristine monolayer makes it magnetic and narrow band gap semiconductor. The spin-polarized character of the monolayer with defects is clearly captured by the tunneling current calculated in the STM-like setup. A relatively low thermal conductivity has been observed in monolayers with defects as compared to pristine form resulting in enhanced room temperature figure of merit as high as 6.24 and 1.30 respectively. The results presented open up a new window for the use of monolayer MoS2 in electronic devices, thermal management and thermoelectric devices