Department Of Physics

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Author: search.filters.author.Gupta, Sanjeev K.Has files: Yes

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    Si and Ge based metallic core/shell nanowires for nano-electronic device applications
    (Nature Publishing Group, 2018) Bhuyan, Prabal Dev; Kumar, Ashok; Sonvane, Yogesh; Gajjar, P.N.; Magri, Rita; Gupta, Sanjeev K.
    One dimensional heterostructure nanowires (NWs) have attracted a large attention due to the possibility of easily tuning their energy gap, a useful property for application to next generation electronic devices. In this work, we propose new core/shell NW systems where Ge and Si shells are built around very thin As and Sb cores. The modification in the electronic properties arises due to the induced compressive strain experienced by the metal core region which is attributed to the lattice-mismatch with the shell region. As/Ge and As/Si nanowires undergo a semiconducting-to-metal transition on increasing the diameter of the shell. The current-voltage (I-V) characteristics of the nanowires show a negative differential conductance (NDC) effect for small diameters that could lead to their application in atomic scale device(s) for fast switching. In addition, an ohmic behavior and upto 300% increment of the current value is achieved on just doubling the shell region. The resistivity of nanowires decreases with the increase in diameter. These characteristics make these NWs suitable candidates for application as electron connectors in nanoelectronic devices.
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    Highly infrared sensitive VO2 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 VO2 nanowires. 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 sensor. ? 2018 the Owner Societies.
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    2D-HfS 2 as an efficient photocatalyst for water splitting
    (Royal Society of Chemistry, 2016) Singh, Deobrat; Gupta, Sanjeev K.; Sonvane, Yogesh; Kumar, Ashok; Ahuja, Rajeev
    Two dimensional monolayer nanostructures for water splitting solar photocatalysts are drawing more attention due to their extraordinary properties. Using first principles calculations we have systematically investigated the structural, electronic and vibrational properties of corresponding HfS2 monolayers in both hexagonal (1H) and trigonal (1T) phases. The most stable adsorption configurations and adsorption energies are calculated. The adsorption energy of H2O on the substrate is 646.53 kJ mol−1 for the 1H-phase and 621.65 kJ mol−1 for the 1T-phase of HfS2. This shows that H2O molecules have a stronger interaction with the HfS2 substrate. The calculated redox potentials of H2O splitting lie properly astride the valence and conduction bands, suggesting that the monolayers of 1H- and 1T-HfS2 show the same characteristics as a photocatalyst for water splitting. Furthermore, we also calculated that the optical band gaps for the 1H and 1T phases of HfS2 are 2.60 eV and 3.10 eV, respectively. We have also calculated Raman spectrum signatures of the monolayer 1H and 1T-phase of the in-plane vibrational mode of the Hf and S atoms (E1g) and the out-of-plane vibrational mode of S atoms (A1g and A2u). Our work suggests that a lot more research and attention in this field is needed for the practical application of the material as visible light active photocatalysts.