Underpotential—overpotential transition phenomena in metal deposition processes

The transition phenomena in metal deposition processes have been studied in the system Ag(hkl)/Pb²⁺ by potentiostatic pulse experiments from the underpotential to the overpotential range. The analysis of the current-time transients indicates a model of progressive nucleation and hemispherical diffusion to the growing 3-D crystallites. An important influence of the initial state in the underpotential range on the nucleation rate has been found. Furthermore, the nucleation rate strongly depends on the overvoltage and on the substrate nature. All experimental results are explained by a stepwise bulk phase formation process including rearrangement of adatoms in the 2-D adsorbed layer, formation of critical clusters and further rearrangement and growth forming epitaxially orientated 3-D crystallites. The nucleation process must be treated by an atomistic model due to the derived low number of atoms in the critical cluster.