Mechanism for the formation of Au-Cu alloy multiply twinned particles formed in the region of UPD of Cu2+ in perchloric acid solution

Au-Cu alloy icosahedral and decahedral particles (multiply twinned particles) are formed by codeposition of Au and Cu ions on the carbon electrode at positive potentials which are located in the region of underpotential deposition (UPD) of Cu2+ on the Au electrode, where only Au fee single crystal particles grow but neither decahedral particles nor icosahedral particles of pure Au are Formed. It is suggested that due to the adsorption of Cu+ on the surface of Au overlayer of the alloy particles, the surface electron density increases. For a stable surface state the surface atoms are contracted. This is similar to the reconstruction occurring on the Au(111) electrode surface at negative potentials. Due to the contraction of the surface atoms, there is a possibility of the formation of the Au-Cu alloy icosahedral and decahedral particles. It is supposed that the growth mode of the Au-Cu alloy particles formed in solution in the region of UPD of Cu2+ is a layer-by-layer growth. (C) 1998 Elsevier Science B.V. All rights reserved.