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

Abstract

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 α eff(Co) Cu increasing from 0.30 to 0.8 and β(Co) Cu=0.68±0.09 for 10< t<1000 s. Graphite gives rise to 0.77≥ α≥0.66 and β=0.12±0.03 for 10< t<250 s corresponding to a stable interface growth whose dynamics is similar to that of the linear molecular beam epitaxy mode bearing a non-conservative noise.