Publications (2)8.37 Total impact
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Article: Formation of Palladium Nanofilms using Electrochemical Atomic Layer Deposition (E-ALD) with Chloride Complexation.
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ABSTRACT: Pd thin films were formed by electrochemical atomic layer deposition (E-ALD) using surface limited redox replacement (SLRR) of Cu underpotential deposits (UPD) on polycrystalline Au substrates. An automated electrochemical flow deposition system was used to deposit Pd atomic layers using a sequence of steps referred to as a cycle. The initial step was Cu UPD, followed by its exchange for Pd ions at open circuit, and finishing with a blank rinse, to complete the cycle. Deposits were formed with up to 75 cycles, and displayed proportional deposit thicknesses. Previous reports by this group indicated excess Pd deposition at the flow cell ingress, from EPMA. Those results suggested the SLRR mechanism was not direct transfer between a Cu(upd) atom and a Pd(2+) ion which would take its position. Instead, it was proposed that electrons are transferred through the metallic surface to reduce Pd(2+) ions near the surface where their activity is highest. It was proposed that if the cell was filled completely before a significant fraction of the Cu(upd) atoms had been oxidized, the deposit would be homogeneous. Previous work with EDTA indicated the hypothesis had merit, but it proved to be highly sensitive to the EDTA concentration. In the present study chloride was used to complex Pd(2+) ions, forming PdCl(4)(2-), to slow the exchange rate. Both complexing agents led to a decrease in the rate of replacement, producing more homogeneous films. While use of EDTA improved homogeneity, it also decreased the deposit thickness by a factor of 3 compared with chloride.Langmuir 12/2012; · 4.19 Impact Factor -
Article: Aqueous electrodeposition of Ge monolayers.
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ABSTRACT: The electrodeposition of germanium on Au(111) in aqueous solutions has been investigated by means of cyclic voltammetry, Auger electron spectroscopy, and in situ scanning tunneling microscopy (STM). The data yield a picture of germanium deposition, which starts with the formation of two well-ordered hydroxide phases, with 1/3 ML and 4/9 ML coverages upon initial reduction of the Ge(IV) species (probably H(2)GeO(3) at pH 4.7). Those structures appear to result from a three-electron reduction to form surface-limited structures with (square root(3) x square root(3))R30 degrees or (3 x 3) unit cells, respectively. Further reduction, probably in a two-electron process from the hydroxide structures, resulted in a germanium hydride structure, again surface-limited, with a coverage of close to 0.8 ML. The hydride structure is very flat, though with the periodic modulation characteristic of a Moiré pattern. Longer deposition times and lower potentials resulted in increased coverage of Ge in some cases, but with apparently limited coverage as a function of pH. The maximum Ge coverage, about 4 ML, was observed using a pH 9.32 deposition solution. At potentials negative of the Moiré pattern, about -850 mV versus Ag/AgCl, a "corruption" of the smooth Moiré pattern occurred. This roughening appears to mark the initial formation of a Au-Ge alloy, accounting for the observation of coverage in excess of that needed to form the Moiré pattern at some pH values.Langmuir 11/2009; 26(4):2877-84. · 4.19 Impact Factor
