COPPER DEPOSITION ONTO AU(III) IN THE PRESENCE OF THIOUREA

The influence of thiourea on the initial stages of Cu deposition on an Au(111) electrode has been studied by potential-step experiments and by in situ scanning tunneling microscopy. It is shown that adsorbed th iourea prevents the formation of a uniform Cu monolayer at underpotent ials. The resulting island structure of the underpotential deposited l ayer provides many nucleation sites on the gold terraces and hence aff ects the nucleation habit of bulk Cu markedly. From an analysis of the current transients the critical nucleation parameters, size, and free enthalpy of formation of the critical nucleus, have been derived. The possible role of thiourea in the observed changes of the nucleation p arameters and the deposition rates with the additive concentration is discussed.