The silver upd on gold(111) revisited

The adsorption of silver onto Au(111) and stepped Au(111) in sulphuric acid has been investigated in the underpotential deposition (upd) region using cyclic voltammetry in combination with UHV-based methodologies. We report d ata showing that the first stage of silver upd is strongly dependent on the superficial state of the substrate and on the formation of a Ag-Au surface alloy. In the absence of the surface alloy, the sharp intense upd peak obt ained at 0.53 V (vs. Ag+ \ Ag) is associated with the deposition of Ag on A u terraces. Potential cycling in the upd region introduces some surface def ects and gradually transforms the surface into a surface alloy phase leadin g to the appearance of a silver upd peak at 0.61 V (vs. Ag+ \ Ag). An unusu al temperature dependence of the kinetics of surface alloy formation is rep orted and explained by considering that the rate of surface alloying depend s strongly on the concentration of the surface defects and that self-anneal ing of surface defects takes place. In the light of these findings, voltamm etric data from previous studies of silver on Au(111) are discussed. (C) 20 00 Elsevier Science S.A. All rights reserved.