Decahedral and icosahedral Cu-Au alloy particles grown under a controlled-potential region in acid solutions

Abstract

Decahedral and icosahedral Cu-Au alloy particles have been formed by electrochemical deposition of Cu and Au in perchloric acid and sulfuric acid solutions at electrode potentials where formation of decahedron and icosahedron Au particles has not been previously observed. This observation is thought to occur due to a contraction of the Au overlayer, induced by the presence of an incompletely discharged ${\mathrm{Cu}}^{+}$ ion deposited on the Au overlayer of the alloy particles in the underpotential deposition region of Cu. This phenomenon is therefore analogous to the alkali-metal-induced reconstruction of Au surfaces. However, decahedral and icosahedral Cu-Au alloy particles were not observed in the Cu-Au alloy particles when the Cu content of the alloy exceeded 30%. It is known that the topmost layer of the reconstructed Au(111) surface is contracted by about 4% and that the lattice spacing of the Cu-Au alloy containing 30% Cu is shortened by about 3% with respect to the Au bulk lattice. Therefore, the lattice mismatch between the Au overlayer and the substrate of Cu-Au alloy particles containing more than 30% Cu is small enough so that no decahedral and icosahedral particles are formed.