The electrodeposition of cobalt, nickel and Ni-Co alloys was studied by electrochemical techniques. Cyclic voltammetry and current transient measurements were used to characterize the Co-Ni system in other to obtain the nucleation and growth mechanism. The cyclic voltammetry results clearly showed that electrodeposition of cobalt, nickel and Co-Ni alloy is diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Co and Ni are shifted to more cathodic potentials in the Co-Ni alloy system. In addition, the current transients revealed that nucleation mechanism is instantaneous with a typical three-dimensional (31)) nucleation and growth process. The number of nucleation sites is increased with the overpotential and nickel or cobalt concentration. It was found that addition of nickel sulfate to cobalt solution, resulted in increasing the number of nucleation sites and therefore the nucleation rate of the Co-Ni alloy system is increased. However, AFM analysis showed that alloying cobalt thin films with nickel changed the microstructure. In this condition, a large number of equally sized spherical grains are observed in single cobalt deposits, while the rectangular particles are deposited in the Co-Ni alloy system as layer-by-layer deposition. (c) 2006 Elsevier B.V. All rights reserved.