MECHANISM FOR THE FORMATION OF AU-CU ALLOY MULTIPLY TWINNED PARTICLESFORMED IN THE REGION OF UPD OF CU2-ACID SOLUTION( IN PERCHLORIC)

Au-Cu alloy icosahedral and decahedral particles (multiply twinned par ticles) are formed by codeposition of Au and Cu ions on the carbon ele ctrode at positive potentials which are located in the region of under potential 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 surfac e state the surface atoms are contracted. This is similar to the recon struction occurring on the Au(111) electrode surface at negative poten tials. Due to the contraction of the surface atoms, there is a possibi lity of the formation of the Au-Cu alloy icosahedral and decahedral pa rticles. It is supposed that the growth mode of the Au-Cu alloy partic les formed in solution in the region of UPD of Cu2+ is a layer-by-laye r growth. (C) 1998 Elsevier Science B.V. All rights reserved.