Alloy formation in the system Au(1 1 1)/Cd during the UPD process

Abstract

The Au-Cd alloy formation in the course of Cd underpotential deposition (UPD) in the system Au(111)/Cd2+, SO42- has been studied by conventional electrochemical techniques and in situ STM. The long time polarization experiments and the current-potential desorption spectra have indicated that the alloy can be formed at relatively high underpotentials with the formation of 2D Cd islands as was observed by in situ STM images. These islands grow and coalesce at a constant potential with the subsequent formation of new 2D islands on top of the partially formed first Cd monolayer. Atomically resolved images of these islands have revealed an hexagonal atomic structure with an interatomic distance of 0.29±0.01 nm. The dissolution of these features occurs together with the formation of many holes of monatomic height which induces a surface roughening. The alloy formation is explained considering a place exchange process between the Au atoms and the adsorbed Cd atoms followed by solid state diffusion of these atoms through the alloyed phase.