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

The adsorption of sulfate anions ( S O 4 2 − ) and copper cations on Au(1 1 1) from CuSO 4 containing H 2 SO 4 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(1 1 1) is discussed in the context of results obtained for sulfate on bare Au(1 1 1) and Cu(1 1 1) electrodes in H 2 SO 4 solution. [ABSTRACT FROM AUTHOR]