A determination of copper overlayer structures on Au(111) in the presence of electrolyte additives

Abstract

Cyclic voltammetry and scanning tunnelling microscopy (STM) were used to study the influence of chloride and crystal violet on the underpotential deposition (upd) of copper on Au(111). As previously reported, a (√3 × √3)R30° copper overlayer has been characterized in the absence of additives and this has been related to the first upd peak. At low chloride concentrations this first upd peak splits into two partially overlapping peaks and a more densely packed copper structure appears alongside the (√3 × √3)R30° domains. The splitting of this first voltammetric peak disappears at high chloride concentrations and only the more densely packed copper overlayer is observed. The STM images are consistent with either a (5 × 5) or 1.29 × 1.29) structure. Crystal violet is a cationic organic dye, with a chloride counterion. It has a marked influence on the voltammetry, with the first upd peak occurring at significantly more negative potentials. Even at a low crystal violet concentration, which corresponded to the lowest chloride concentration (where joint domains were always seen), only the (5 × 5) (or (1.29 × 1.29)) structure was observed. This clearly indicates the pronounced effect arising from the adsorption of the organic cation.