Influence of potential on the electrodeposition of Co on Au(111) by in situ STM and reflectivity measurements

We study the influence of the deposition potential on the electrochemical growth of Co on Au(111) in the thickness range 0-8 atomic layers (ML). In-situ STM observations evidence two growth regimes which depend on the deposition potential: at potentials < -1.2 VMSE, Co grows 2D with the initial formation of biatomic islands which rapidly cover the entire Au surface, followed by layer-by-layer growth; at potentials > -1.20 VMSE, Co grows 3D with the formation of large multilayer islands with flat top. In situ fast STM imaging of the Co dissolution process evidences a remarkable thickness dependence of the dissolution potential. Complementary electrochemical and in situ optical reflectivity characterizations of Co dissolution as a function of the Co thickness suggest that the equilibrium potential Co/Co²⁺ on Au is shifted by∼-30 mV with respect to that measured on Co. This value is discussed in terms of Co-substrate binding energy.