Observation of growth mode dependence on over-potential values: a combination of in-situ optical monitoring and ex-situ atomic force microscopy characterization.

We study the over-potential electrodeposition of Pb on Cu(100) using a combination of an \textit{in-situ} oblique-incidence reflectivity difference technique and \textit{ex-situ} atomic force microscopy. We identified two distinctly different over-potential growth modes that depend on the values of the overpotential. We have characterized the morphology corresponding to the two growth modes using AFM. At a high over-potential there is even growth of small clusters across the monolayer thick under-potential deposited (UPD) Pb covered Cu(100) surface. At lower over-potentials (a fraction of a volt from the value for UPD), we observed much larger 3-D clusters, more than 400 nm in height and separated by an averaged distance of one micron.