Electrocrystallisation of cobalt during preparation of Co/Cu multilayers

The electrocrystallisation of cobalt onto a glassy carbon electrode from cobalt sulphate electrolytes either with or without the addition of a small amount of copper ions was investigated through the electrochemical techniques of cyclic voltammetry and chronoamperometry. Voltammetric results showed that the cobalt deposits obtained were impure and the overpotential for cobalt nucleation was low for electrolyte with a small amount of copper ions. Analysis of the current–time transients by chronoamperometry indicated that the nucleation mechanism of cobalt in cobalt sulphate solution occurred by a combination of two different kinds of parallel nucleation processes, instantaneous or progressive nucleation with two-dimensional or three-dimensional growth, which depended on the overpotential applied. However, in the presence of copper ions, the nucleation mechanism was in accordance with 3D growth under diffusion control. Progressive nucleation occurred at a lower overpotential and instantaneous nucleation at a higher overpotential. The deviation of the experimental data from the theoretical model was explained.