Two‐dimensional phase transitions in electrochemically formed adlayers on gold

Two‐dimensional phase transitions occurring during electrodeposition of the first Cu monolayer onto Au(111) at underpotentials or during adsorption of coumarin from solution at Au(111) and the reconstructed Au(100)‐ (hex) electrodes have been studied by cyclic voltammetry and potential step experiments. Rising current transients were observed for both systems, indicating the presence of nucleation‐and‐growth phenomena during monolayer formation. However, phase transitions in the adlayers were observed only for the densely packed gold surfaces, and not for the more open surfaces of Au(100)‐(1×1) or Au(110). A comparison between experiment and classical model transients revealed that surface imperfections may have to be taken into account when working with solid electrodes, rather than with mercury for which these models have been derived.