Deposition of copper and sulfate on Au(1 1 1): New insights

Abstract

The adsorption of sulfate anions (SO42−) and copper cations on Au(111) from CuSO4 containing H2SO4 solution was investigated by cyclic voltammetry (CV) and scanning tunneling microscopy (STM). The underpotential deposition from solution results first in the formation of 2/3 monolayer of copper with the well known (3×3) structure of sulfate followed by the completion of the first copper monolayer at lower potentials. Just after formation of 1ML of Cu STM reveals a disordered surface. At more negative potential values, already in the overpotential deposition region, the STM images reflect a (3×7) sulfate structure on terraces of the first pseudomorphic Cu layer, a (3×3)-like structure on terraces of the second uncompleted Cu layer with sulfate anions residing in atomic vacancies, and the known Moiré structure on terraces of the multi-layer Cu deposit. The formation of the (3×7) sulfate structure on pseudomorphic monolayer Cu terraces on Au(111) is discussed in the context of results obtained for sulfate on bare Au(111) and Cu(111) electrodes in H2SO4 solution.