Electrodeposition and impedance spectroscopy characterization of ZnO nanowire arrays

An overview of the electrodeposition of ZnO nanowire arrays from the reduction of dissolved molecular oxygen in zinc chloride solutions was reported. In spite of the internal structure of ZnO which favours the anisotropic growth along the [0001] direction, the change in the local composition of the electrolyte around the nanowire during the electrodeposition was proposed as a major parameter to affect the nanowire growth mechanism. The influence of the ratio between the O2 reduction rate and the diffusion of Zn2+ to the cathode was emphasized. Due to the particular morphology of the nanowire arrays, no lateral growth was observed when the reduction of O2 was relatively fast, while the corresponding deposition efficiency was very low. The decrease of the O2 reduction rate resulted in an enhancement of the deposition efficiency. The highest efficiencies (40–55%) were attained by using high chloride concentrations ([KCl] = 3.4 M) resulting not only in an enhancement of the longitudinal growth, but also in a considerable lateral growth. The influence of the electrodeposition conditions on the donor density of ZnO nanowires was investigated by using electrochemical impedance spectroscopy. Donor densities from 5 × 1019 cm–3 to 3 × 1020 cm–3 were obtained for as deposited samples. They decreased to values in the range of 1017–1018 cm–3 after annealing in air (1 hour at 450 °C). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

ZnO Nanowires, Nanotubes, and Complex Hierarchical Structures Obtained by Electrochemical Deposition

Increasing the aspect ratio of ZnO nanostructures is one possible strategy to improve their thermoelectric properties. ZnO nanostructures with one-dimensional (1D) and three-dimensional (3D) morphologies were obtained using electrochemical deposition. Adjusting various deposition parameters made it possible to obtain arrays of vertically aligned ZnO nanowires (NWs) with controlled dimensions, density, and electrical properties. The concentrations of zinc or chloride ions in the solution were found to be key parameters. ZnO NWs were transformed into ZnO nanotubes (NTs), with an increased aspect ratio compared with the NWs, by selectively dissolving the core of the ZnO NWs in a concentrated KCl solution. The aspect ratio was strongly increased when the ZnO NWs were hierarchically organized in a 3D morphology. The synthesis of thin films composed of ordered hollow urchin-like ZnO NW structures was performed by combining the electrochemical deposition and polystyrene sphere templating methods. The electronic properties of the urchin-like ZnO structures were investigated by means of photoluminescence and transmission measurement

Étude structurale de CaPb (OH)6 et CdPb (OH)6

Synthetical CaPb (OH)₆ and CdPb (OH)₆ compounds have a structure issued from the ReO₃ type, as other AB (OH)₆ compounds : In (OH)₃, hexahydroxistannates, hexahydroxiantimonates... CaPb (OH)₆ and CdPb (OH)₆ have the cubic space group symmetry T[h]²-Pn₃. Structural intensities refinement has been performed by the least squares method. There is good agreement between observed and calculated X-Ray intensities of powder diffraction. The structural description is : CaPb (OH)₆ : Pn₃, a = 8.252 Å, origin at 3, Ca : 4 b, Pb : 4 c, O : 24 h (x ~ 0.083, y ~ — 0.078, z ~ 0.263). CdPb (OH)₆ : Pn₃, a = 8.150 Å, origin at 3, Cd : 4 b, Pb : 4 c, O : 24 h (x ~ 0.102, y ~ — 0.053, z ~ 0.262). The hydrogen atomic positions were not determinated. Comparison with other AB (OH)₆ compounds, infrared spectroscopy investigations confirm the existence of hydroxyl groups OH, hydrogen bonds and additional molecular water enclosed in the structure of CaPb (OH)₆ and CdPb (OH)₆. In the far infrared region we have shown, by means of the correlation chart method of factor group analysis, that crystals are composed of Pb (OH)₆⁻⁻ polyatomic ions.Les hexahydroxyplombates de métaux divalents CaPb (OH)₆ et CdPb (OH)₆ appartiennent à la famille des hydroxy des AB (OH)₆ dont les structures dérivent de celle de ReO₃ ; CaPb (OH)₆ et CdPb (OH)₆ ont une structure cubique simple de groupe spatial T[h]²-Pn₃. L'affinement cristallographique a été réalisé par la méthode des moindres carrés à partir des intensités de rayons X de diffraction de poudre. Les résultats de l'étude structurale sont : CaPb (OH)₆ : Pn₃, a = 8,252 Å, origine en [-3], Ca : 4 b, Pb : 4 c, O : 24 h (x ~ 0,083, y ~ — 0,078, z ~ 0,263). CdPb (OH)₆ : Pn₃, a = 8,150 Å, origine en [-3], Cd : 4 b, Pb : 4 c, O : 24 h (x ~ 0,102, y ~ — 0,053, z ~ 0,262). Les positions des atomes d'hydrogène n'ont pas pu être déterminées. L'étude des spectres d'absorption infrarouge de CaPb (OH)₆ et CdPb (OH)₆ a permis de confirmer l'existence de groupements hydroxyles OH, de liaisons hydrogènes et d'eau moléculaire supplémentaire « encagée » dans la structure. Dans le domaine de l'infrarouge lointain, l'utilisation de la « méthode de corrélation » montre que les cristaux contiennent des entités moléculaires Pb (OH)₆⁻⁻.Lévy-Clément Claude, Billiet Yves. Étude structurale de CaPb (OH)6 et CdPb (OH)6. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 99, 6, 1976. pp. 361-372

Sensitization of ZnO nanowire arrays with CuInS < sub>2 < /sub> for extremely thin absorber solar cells < sup>a) < /sup&gt

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