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Amirav L.,University of California at Berkeley | Oba F.,University of California at Berkeley | Aloni S.,Material Science Division | Alivisatos A.P.,University of California at Berkeley
Angewandte Chemie - International Edition | Year: 2015

Reported is the design and modular synthesis of a dual metal-dual semiconductor heterostructure with control over the dimensions and placement of its individual components. Analogous to molecular synthesis, colloidal synthesis is now evolving into a series of sequential synthetic procedures with separately optimized steps. We detail the challenges and parameters that must be considered when assembling such a multicomponent nanoparticle, and their solutions. This multicomponent nanosystem, Ru-CdSe@CdS-Pt, was designed to achieve charge carrier separation and directional transfer across different interfaces toward two separate redox catalysts. This heterostructure may potentially serve as a nanometric closed circuit photoelectrochemical cell. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Baruah B.J.,D R College | Bora M.N.,D R College | Saikia L.,Material Science Division | Saikia D.,Sibsagar College | And 2 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2015

A number of researchers have been synthesising thin films of PbS on glass substrates by reaction of 1 M CH4N2S with of 0.50 M Pb(CH3COO)2.3H2O complexed by 1 M triethanolamine (TEA) at different deposition temperatures and reported various temperature dependent properties of the films. In our work, we followed the same recipe but reduced the concentration of Pb(CH3COO)2.3H2O by 0.10 M. The pH of the bath was adjusted at 12. The deposition has been carried out at five different temperatures—30, 40, 50, 64 and 70 °C. We wish to study how structural, optical and electrical properties of the films prepared with reduced concentration of Pb(CH3COO)2.3H2O change with temperature. We have observed that at 30 and 40 °C, no crystalline PbS phase was formed, only elemental S was detected. The PbS phase formation was noticed only from 50 °C. The elemental S has been subdued and the crystalline PbS phase formation has been enhanced with increase of temperature. The average crystallite sizes were determined from XRD by Debye–Scherrer formula, lattice constants from Nelson–Riley plot, band gaps by the derivative method and electrical conductivities from current–voltage characteristics. It has been found that with the increase of deposition temperature, the crystallite size increases, strain decreases, band gap reduces and conductivity improves. The average crystallite sizes were found 35.79, 42.51 and 42.67 nm at 50, 64 and 70 °C respectively. The band gaps for these three films were noted as 1.74, 1.67 and 1.66 eV respectively indicating blue-shift from the bulk value. The tail widths of localised states in the forbidden band were observed in the range of (0.70–0.76) eV. The strains in the films were ~10−3 and conductivities were ~10−7–10−6 (Ω cm)−1. © 2015 Springer Science+Business Media New York

Das P.K.,Jadavpur University | Chowdhury A.,Jadavpur University | Mandal N.,Jadavpur University | Arya A.,Material Science Division
Philosophical Magazine | Year: 2016

Using DFT calculations, this study investigates the pressure-dependent variations of elastic anisotropy in the following SnO2 phases: rutile-type (tetragonal; P42/mnm), CaCl2-type (orthorhombic; Pnnm)-, α-PbO2-type (orthorhombic; Pbcn)- and fluorite-type (cubic; Fm-3m). Experimentally, these polymorphs undergo sequential structural transitions from rutile-type → CaCl2-type → α-PbO2-type → fluorite-type with increasing pressure at 11.35, 14.69 and 58.22 GPa, respectively. We estimate the shear anisotropy (A1 and A3) on {1 0 0} and {0 0 1} crystallographic planes of the tetragonal phase and (A1, A2 and A3) on {1 0 0}, {0 1 0} and {0 0 1} crystallographic planes of the orthorhombic phases. The rutile-type phase shows strongest shear anisotropy on the {0 0 1} planes (A2 > 4.8), and the degree of anisotropy increases nonlinearly with pressure. In contrast, the anisotropy is almost absent on the {1 0 0} planes (ie A1 ~ 1) irrespective of the pressure. The CaCl2-type phase exhibits similar shear anisotropy behaviour preferentially on {0 0 1} (A3>5), while A1 and A2 remain close to 1. The α-PbO2-type phase shows strikingly different elastic anisotropy characterised by a reversal in anisotropy (A3 >1 to< 1) with increasing pressure at a threshold value of 38 GPa. We provide electronic density of states and atomic configuration to account for this pressure-dependent reversal in shear anisotropy. Our study also analyses the directional Young’s moduli for the tetragonal and orthorhombic phases as a function of pressure. Finally, we estimate the band gaps of these four SnO2 phases as a function of pressure which are in agreement with the previous results. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Researchers at the U.S. Naval Research Laboratory (NRL), Optical Sciences Division, in collaboration with the laboratory's Material Science Division, for the first time have demonstrated successful detection of acoustic emission from cracks in riveted lap joints using a distributed feedback fiber laser-acoustic emission sensor.

Choudhuri G.,Quality Assurance Division | Jagannath,Theoretical Physics Division | Kiran Kumar M.,Material Science Division | Kain V.,Material Science Division | And 5 more authors.
Journal of Nuclear Materials | Year: 2013

The effects of Fe addition in the range of 300-1250 ppm in cold worked stress-relieved Zr-2.5Nb pressure tube on oxidation and hydrogen pick up behavior have been studied after 415 C steam autoclaving. Microstructure and micro-chemistry of second phase and precipitates were characterized using electron microscope. Addition of 800 ppm Fe in Zr-2.5Nb alloy led to better oxidation resistance. With further addition of Fe no significant improvement of oxidation resistance was observed but hydrogen-pickup was found to increase. Zr-Nb-Fe bearing precipitates were observed in Zr-2.5Nb alloy containing 800 ppm Fe. Further addition of Fe led to formation of Zr-Fe intermetallic. The chemical state of oxide has been determined by X-ray photo electron spectroscopy. Grazing Incidence X-ray Diffraction revealed that oxide in alloys with higher Fe, contained a higher fraction of tetragonal-Zirconia which is indicative of a protective oxide film and hence better oxidation resistance of the alloy. © 2013 Elsevier B.V. All rights reserved.

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