THE INITIAL-STAGES OF COPPER DEPOSITION ON AG(111) - AN STM STUDY

The initial stages of Cu deposition on Ag(111) from a sulfate-containing solution has been studied by in-situ scanning tunneling microscopy (STM) for low and high overpotentials. Very surprisingly, at low overpotentials Cu is preferentially deposited at the terraces of the substrate rather than at steps and it grows two-dimensional. At high overpotentials, Cu nucleates at surface defects such as monoatomic high steps and forms three-dimensional clusters, very much like in the case of Cu on Au(111). At low overpotentials the first layer of Cu grows pseudomorphic on Ag(111) and it may cover the whole surface before the second Cu layer starts to grow on top. Yet, no underpotential deposition (UPD) is observed for Cu on Ag(111). This very unusual nucleation-and-growth behaviour is explained by the specific adsorption of sulfate at the steps of Ag(111), which blocks these sites for Cu deposition, and by a delicate balance of adatom-adatom and adatom-substrate interactions, which causes the UPD shift to disappear.