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 d ifferent electrochemical techniques and in-situ scanning tunneling mic roscopy (STM) with lateral atomic resolution. Surface reconstruction o f electrochemically polished Au(100) substrates was observed at relati vely positive potentials showing an influence of the electrode pretrea tment, i.e. crystal imperfection density, on the potential-induced lif ting of this process, which starts at steps and crystal defects. The r esults indicate that UPD of Ag also leads to a lifting of the surface reconstruction. The electrochemical and in-situ STM results are interp reted in terms of the formation of 2D domains which consist of well-or dered 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 g rowth (Frank-van der Merwe) mechanism at low overpotentials is observe d which is followed by a multilayer growth mode at higher overpotentia ls. The results indicate that the layers are generated by a spiral gro wth mode caused by screw dislocations of the real Au(100) substrate wh ich are inherited by the epitaxial 3D Ag deposit.