SILVER ELECTRODEPOSITION ON AU(100) - STRUCTURAL ASPECTS AND MECHANISM

The underpotential deposition (UPD) and overpotential deposition (OPD) of silver on Au(100) single crystal faces have been investigated by different electrochemical techniques and in-situ scanning tunneling microscopy (STM) with lateral atomic resolution. Surface reconstruction of electrochemically polished Au(100) substrates was observed at relatively positive potentials showing an influence of the electrode pretreatment, i.e. crystal imperfection density, on the potential-induced lifting of this process, which starts at steps and crystal defects. The results indicate that UPD of Ag also leads to a lifting of the surface reconstruction. The electrochemical and in-situ STM results are interpreted in terms of the formation of 2D domains which consist of well-ordered Au(100)-(1 x 1)Ag adlayers and of Au-Ag surface alloy after long-time polarization. These domains act as precursors for the 3D silver phase formation in the OPD range. Initially a monolayer-by-monolayer growth (Frank-van der Merwe) mechanism at low overpotentials is observed which is followed by a multilayer growth mode at higher overpotentials. The results indicate that the layers are generated by a spiral growth mode caused by screw dislocations of the real Au(100) substrate which are inherited by the epitaxial 3D Ag deposit.