THE ELECTROREDUCTION KINETICS OF THE HYDROUS GOLD OXIDE LAYERS AND GROWTH MODES AND ROUGHNESS OF THE ELECTROREDUCED GOLD OVERLAYERS

The electroreduction of thick gold oxide layers yielding metallic gold overlayers with different roughness factors is studied by using potentiodynamic and potentiostatic techniques combined with scanning electron microscopy. The electroreduction process involves at least the electroreduction of an inner relatively thin oxide layer followed by the electroreduction of an outer thick hydrous gold oxide layer. The latter involves most of the electroreduction charge and the kinetics of the reaction can be described through a nucleation and 3-D growth mechanism which operates under charge transfer rate control at low overpotentials, and under diffusion control at higher overpotentials. The physical mechanism implies the death of growing nuclei as the oxide layer electroreduction takes place. Under constant electroreduction potential the roughness of the resulting gold overlayers increases according to electroreduction overpotential, as one should expect for the diffusion controlled growth mode of the gold overlayer. © 1990.