Department Of Physics

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    Structural, electrical properties and dielectric relaxations in Na+-ion-conducting solid polymer electrolyte
    (Institute of Physics Publishing, 2018) Arya, A.; Sharma, A.L.
    In this paper, we have studied the structural, microstructural, electrical, dielectric properties and ion dynamics of a sodium-ion-conducting solid polymer electrolyte film comprising PEO8-NaPF6+ x wt. % succinonitrile. The structural and surface morphology properties have been investigated, respectively using x-ray diffraction and field emission scanning electron microscopy. The complex formation was examined using Fourier transform infrared spectroscopy, and the fraction of free anions/ion pairs obtained via deconvolution. The complex dielectric permittivity and loss tangent has been analyzed across the whole frequency window, and enables us to estimate the DC conductivity, dielectric strength, double layer capacitance and relaxation time. The presence of relaxing dipoles was determined by the addition of succinonitrile (wt./wt.) and the peak shift towards high frequency indicates the decrease of relaxation time. Further, relations among various relaxation times () have been elucidated. The complex conductivity has been examined across the whole frequency window; it obeys the Universal Power Law, and displays strong dependency on succinonitrile content. The sigma representation () was introduced in order to explore the ion dynamics by highlighting the dispersion region in the Cole-Cole plot () in the lower frequency window; increase in the semicircle radius indicates a decrease of relaxation time. This observation is accompanied by enhancement in ionic conductivity and faster ion transport. A convincing, logical scheme to justify the experimental data has been proposed. ? 2018 IOP Publishing Ltd.
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    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.
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    Electronic, Mechanical, and Dielectric Properties of Two-Dimensional Atomic Layers of Noble Metals
    (Springer New York LLC, 2017) Kapoor, Pooja; Kumar, Jagdish; Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.
    We present density functional theory-based electronic, mechanical, and dielectric properties of monolayers and bilayers of noble metals (Au, Ag, Cu, and Pt) taken with graphene-like hexagonal structure. The Au, Ag, and Pt bilayers stabilize in AA-stacked configuration, while the Cu bilayer favors the AB stacking pattern. The quantum ballistic conductance of the noble-metal mono- and bilayers is remarkably increased compared with their bulk counterparts. Among the studied systems, the tensile strength is found to be highest for the Pt monolayer and bilayer. The noble metals in mono- and bilayer form show distinctly different electron energy loss spectra and reflectance spectra due to the quantum confinement effect on going from bulk to the monolayer limit. Such tunability of the electronic and dielectric properties of noble metals by reducing the degrees of freedom of electrons offers promise for their use in nanoelectronics and optoelectronics applications. ? 2016, The Minerals, Metals & Materials Society.