Analysis of the substrate effect on the nucleation and growth mode of electrodeposited cobalt on copper and graphite electrodes

The nucleation, surface growth and roughening of cobalt electrodeposits on a polycrystalline copper and on amorphous graphite substrates have been studied using electrochemical techniques (voltammetry and chrono-amperometry) and surface imaging by Atomic Force Microscopy (AFM). The influence of the substrate nature and surface preparation on the nucleation and growth mode of Co was investigated as a function of deposition potential and Co thickness. The chrono-amperometry analysis of Co deposits on Cu reveals that the nucleation process agrees with the progressive Armstrong model. Graphite substrate leads to a nucleation process described by the instantaneous Scharifker–Hills model. The morphology and topography aspects examined by AFM denote that the roughness exponent α varies with the film deposition time t while a constant value of the growth exponent β is observed with the two substrates. Cu leads to unstable interfaces characterised by an effective roughness αeff(Co)Cu increasing from 0.30 to 0.8 and β(Co)Cu=0.68±0.09 for 10