School Of Basic And Applied Sciences

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    Structural and electronic investigation of metal-semiconductor hybrid tetrapod hetero-structures
    (Springer Verlag, 2017) Haldar, K.K.; Muley, V.Y.; Datar, S.; Patra, A.
    This article highlights the new electronic properties of tetrapod hetero-structures with metal Au core and semiconductor CdSe arms, which is one of the new classes of hybrid metal-semiconductor nanostructures. From the analysis of XRD, HRTEM, HAADF-STEM images, and EDAX line-scan studies, the growth mechanism of all these hetero-structures is proposed. These findings are important from the basic fundamental aspects of understanding the shape control of hetero-structures. Scanning tunneling spectroscopic study confirms the coulomb staircase-like features near Au which is characteristic of Au nanoparticles and the gap increases as we move the tip towards CdSe. Analysis suggests that the resonance tunneling occurs between valance band edge (conduction band edge) of CdSe and coulomb stairs of Au dot. These tetrapod hetero-structures could pave the way for designing new optical-based materials for developing new challenging photonic devices. ? 2017, Springer International Publishing Switzerland.
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    Identifying the preferred interaction mode of naringin with gold nanoparticles through experimental, DFT and TDDFT techniques: Insights into their sensing and biological applications
    (Royal Society of Chemistry, 2016) Singh, Baljinder; Rani, Monika; Singh, Janpreet; Moudgil, Lovika; Sharma, Prateek; Kumar, Sanjeev; Saini, G.S.S.; Tripathi, S.K.; Singh, Gurinder; Kaura, Aman
    In this work, the binding behaviour of naringin-a flavonoid with AuNPs is explained by combining experimental and theoretical approaches. We have systematically analysed the effect of temperature and concentration of naringin and gold (Au) in the formation of naringin stabilized Au nanoparticles (N-AuNPs). The interaction of naringin with gold nanoparticles (AuNPs) is investigated by various techniques such as UV-visible spectroscopy, TEM, FT-IR, XRD and gel electrophoresis. These studies indicate that naringin acts as a reducing and stabilizing agent. Further, we have modelled the two side chains of naringin with the functional groups [C10H7O2] and [C6H5O]-, and identified the lowest energy configurations of these groups with AuNPs with the help of density functional theory (DFT). The [C10H7O2]-Au13 has higher binding energy than [C6H5O]--Au13 and it is attributed to delocalized molecular orbitals in [C10H7O2], hence higher charge transfer to the Au13 cluster. On the basis of the resulting structures, we examine the optical properties using time-dependent density functional theory (TDDFT). We observe significant changes in the optical spectra of the representative structures of side chains with the AuNPs. The peak in the spectra of the Vis region of [C10H7O2]-Au13 undergoes a shift towards lower wavelength in comparison to [C6H5O]--Au13. Natural transition orbitals (NTOs) of hole and particle states of the [C10H7O2]-Au13 conjugate system are localized on [C10H7O2] and Au13, respectively, whereas for the [C6H5O]--Au13 both hole and particle states are localized on the Au13 cluster. These N-AuNPs show their applicability as a sensor for detecting aluminium ions (Al3+) in aqueous solution. These NPs are also found to be biocompatible with normal red blood cells and MDAMB-231 breast carcinoma cell lines, as evaluated from hemolysis and cytotoxicity assays. Thus, naringin offers non-toxic and bio friendly N-AuNPs, which are considered to be the best vehicle for drug release and other possible biomedical and sensing applications. ? 2016 The Royal Society of Chemistry.
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    Core size matters! High Raman enhancing core tunable Au/Ag bimetallic core-shell nanoparticles
    (Springer Verlag, 2017) Paital, D.; Sen, T.; Patra, A.; Haldar, K.K.
    Bimetallic core-shell nanostructures have been attracted tremendous attention due to their ability to form novel materials with unique chemical, optical, and physical properties. Here, we have studied the influence of core size of Au/Ag bimetallic core-shell nanostructures on the Raman enhancement efficiency with the Raman-active probe methylene blue. The surface-enhanced Raman scattering intensity is increased with increase in the core size of Au/Ag bimetallic core-shell nanoparticles. Interestingly, the enhancement factor is found to be 6.58?נ107 for the Au100/Ag core-shell nanoparticles and allows easy detection of analyte methylene blue. Thus, surface-enhanced Raman scattering properties of the metal nanoparticles are significantly enhanced due to the Au/Ag core-shell structures and the enhancement factor is dependent on the size of the core of the bimetallic nanoparticles. ? 2017, Springer International Publishing AG.
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    Shell thickness matters! Energy transfer and rectification study of Au/ZnO core/shell nanoparticles
    (Academic Press Inc., 2016) Haldar, Krishna Kanta; Sen, Tapasi
    In the present study we report the influence of shell thickness on fluorescence resonance energy transfer between Au/ZnO core-shell nanoparticles and Rhodamine 6G dye by steady-state and time-resolved spectroscopy and rectification behaviours. Au/ZnO core-shell nanoparticles with different shell thickness were synthesized in aqueous solution by chemically depositing zinc oxide on gold nanoparticles surface. A pronounced effect on the photoluminescence (PL) intensity and shortening of the decay time of the dye in presence of Au/ZnO core-shell nanoparticles is observed. The calculated energy transfer efficiencies from dye to Au/ZnO are 62.5%, 79.2%, 53.6% and 46.7% for 1.5 nm, 3 nm, 5 nm and 8 nm thickness of shell, respectively. Using FRET process, the calculated distances (r) are 117.8, 113.2 ? 129.9 ? and 136.7 ? for 1.5 nm, 3 nm, 5 nm and 8 nm thick Au/ZnO core-shell nanoparticles, respectively. The distances (d) between the donor and acceptor are 71.0, 57.8, 76.2 and 81.6 ? for 1.5 nm, 3 nm, 5 nm and 8 nm thick core-shell Au/ZnO nanoparticles, respectively, using the efficiency of surface energy transfer (SET). The current-voltage (I-V) curve of hybrid Au/ZnO clearly exhibits a rectifying nature and represents the n-type Schottky diode characteristics with a typical turn-on voltage of between 0.6 and 1.3 V. It was found that the rectifying ratio increases from 20 to 90 with decreasing the thickness of the shell from 5 nm to 3 nm and with shell thickness of 8 nm, electrical transport through the core-shell is similar to what is observed with pure ZnO samples nanoparticles. The results indicated that the Au/ZnO core-shell nanoparticles with an average shell thickness of 3 nm exhibited the maximum energy transfer efficiencies (79.2%) and rectification (rectifying ratio 90). ? 2016
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    Size dependent tunnel diode effects in gold tipped CdSe nanodumbbells
    (American Institute of Physics Inc., 2017) Saraf, Deepashri; Kumar, Ashok; Kanhere, Dilip; Kshirsagar, Anjali
    We report simulation results for scanning tunneling spectroscopy of gold-tipped CdSe nanodumbbells of lengths ?27 ? and ?78 ?. Present results are based on Bardeen, Tersoff, and Hamann formalism that takes inputs from ab initio calculations. For the shorter nanodumbbell, the current-voltage curves reveal negative differential conductance, the characteristic of a tunnel diode. This behaviour is attributed to highly localized metal induced gap states that rapidly decay towards the center of the nanodumbbell leading to suppression in tunneling. In the longer nanodumbbell, these gap states are absent in the central region, as a consequence of which zero tunneling current is observed in that region. The overall current-voltage characteristics for this nanodumbbell are observed to be largely linear near the metal-semiconductor interface and become rectifying at the central region, the nature being similar to its parent nanorod. The cross-sectional heights of these nanodumbbells also show bias-dependence where we begin to observe giant Stark effect features in the semiconducting central region of the longer nanodumbbell. ? 2017 Author(s).