The influence of the first stages of anodic oxidation of p-Si on the mechanism of Co deposition was studied by means of electrochemical techniques and AFM. The surface transformation during the formation of a thin oxide layer on hydrogen-terminated Si was followed by capacitance measurements and related to changes of the electrodeposition mechanism. It was observed that the reduction of Co2+ on oxide free p-Si occurs at the negative side of the flat band potential involving the discharge of photogenerated electrons at the conduction band edge and/or surface state levels. The fort-nation of an oxide film of d(ox) < 2 nm introduces an energy barrier that increases the overpotential for electrodeposition. The morphology of deposits, on the other hand, changes from layer like to grain like after surface oxidation, indicating a substantial modification of the nature and density of nucleation sites. The number density of deposited clusters on an oxidized surface showed a proportionality with the field strength in the oxide, indicating the presence of a certain high-field assisted mechanism in the generation of active sites. (c) 2005 Elsevier Ltd. All rights reserved.