We investigate the influence of chloride Cl − ions in a broad range of chloride concentrations on the kinetics and mechanism of copper electrodeposition from sulfate-based acidic electrolytes. Chloride ions influence copper deposition through two competitive effects: at low Cl − concentration ͑few mM͒, chloride ions depolarize the Cu reduction process, while higher Cl − concentrations induce complexation of copper species and cause a cathodic polarization of the deposition process. Cu reduction proceeds through two parallel mechanisms, a direct two-step reduction and a chloride-mediated route, whose relative importance depends on the amount of chloride present. A transition between these two mechanisms can be identified both by steady-state and impedance methods; however, the chloride concentration at which it occurs depends on the time scale probed by the two techniques. Impedance measurements further demonstrate that the presence of chlorides changes the double-layer structure.

No abstract

Chalcogenides such as bismuth telluride and lead telluride exhibit high thermoelectric figures of merit ZT 1-3 in the bulk because of a combination of high electrical conductivity σ and Seebeck coefficient S, and low thermal conductivity κ, making them attractive for refrigeration and generating electrical power from heat. 4-6 Nanostructuring these materials along one dimension (e.g., nanolayers) has been shown to increase ZT because of size and quantum effects on S, σ, and κ. 7,8 Greater degrees of confinement (e.g., PbTe nanowires with characteristic dimensions <5 nm) 9 are expected to provide higher ZT increases and open up entirely new types of possibilities for novel applications such as cooling nanoscale hotspots in nanodevice interconnections comprising nanowires or nanotubes and creating nanoscale power generators.Growing one-dimensional nanocrystals of chalcogenides with a cubic crystal structure (e.g., PbTe, rocksalt structure) is a challenge because of the necessity of a symmetrybreaking pathway for enabling anisotropic growth. 10 Solvothermal decomposition or polyol reduction yield spherical 11 or cube-shaped 12,13 nanoparticles. Incorporating surfactants provides particle size control, but is ineffective in inducing shape anisotropy because of the high crystallographic degeneracy in cubic crystals. Alternative methods based on oriented attachment of nanoparticles in solution, 14-16 catalystmediated vapor-liquid-solid reactions, 17,18 and inorganic templating have been devised. 19,20 However, nanowire polycrystallinity and template removal issues limit the utility of these routes for fundamental studies and for reaping the maximal benefit of the properties of single crystals for applications. Recently devised sonochemical and autoclavebased techniques, 21-23 e.g., <10 nm diameter nanorods 12 with aspect ratios j7, and formation of single-crystal nanowires through nanoparticle coalescence and ripening, however, are promising approaches. 31 Here, we report a completely new two-step organicinorganic templating method to obtain single-crystal PbTe nanorods with aspect ratios up to 27, at moderate temperatures, without using an autoclave. We exploit anisotropic nanotube growth through organic surfactant templating and transform the nanotubes into single-crystal PbTe nanorods via reaction with a lead salt obviating any subsequent template removal. Nanorod to nanotube conversion has been reported, 25 but the reverse process reported here is new and can be applied to producing anisotropic nanostructures of materials with a cubic structure.In the first step, Te nanotubes were synthesized by solvothermal reduction of TeO 2 in the presence of cetyl ether,

Thin films of Cu-Co alloy exhibiting excellent metallic luster were galvanostatically electrodeposited directly on Si substrates in a single citrate bath containing sulfates of the metal ions. The direct electrodeposition onto n-Si substrates eliminated a processing step, of depositing a conducting layer, if an insulator were to be used as a substrate. In addition, the use of silicon as a substrate is promising in integrating this inexpensive technique with semiconductor microelectronic device fabrication technology. The as-deposited films exhibited giant magnetoresistance (GMR) of 1% false(T=300K,H=10 normalkOefalse) and 5% false(T=10K and H=50 normalkOefalse). The annealed films showed an increase in GMR from 1 to 2.7%. The X-ray diffraction studies of as-deposited metastable films indicate solid solution like behavior following Vegard’s law. However, our magnetic studies evidenced the presence of very fine nanograins of Co in these films. A systematic study of the effect of various processing parameters like deposition current density, bath temperature, and pH on the composition, structure, and microstructure of thin films was carried out to understand the electrodeposition process. Deposition current density and bath temperature have significant control over the composition and microstructure. The pH of the electrolyte seems to affect the topography most. Like physical vapor deposition (PVD), the electrodeposition process yields thin films via a nucleation-controlled growth mechanism. The superiority of the electrodeposition technique over the PVD technique is emphasized. © 2002 The Electrochemical Society. All rights reserved.