An in-situ STM investigation of the underpotential deposition of Ag on Au(111) electrodes

A detailed potentiodynamic and electrochemical scanning tunneling microscopy (ECSTM) study of the system Au(111)/Ag⁺+ HClO₄ is presented. The growth and dissolution dynamics of the first underpotentially deposited Ag monolayer were followed in situ with monolayer (ML) height resolution. For newly prepared Au substrates, the cyclic voltammetry consists of three distinct underpotential deposition (UPD) peaks, with the main peak located at 600 mV. The coulometry indicates that a coverage of 0.8 ML is obtained at an underpotential of 75 mV. For freshly deposited Au films, the formation of a complete Ag overlayer is shown by ECSTM to occur by a step growth mechanism at the 600 mV peak. No further morphology changes were observed during subsequent deposition between 550 and 100 mV indicating that the UPD peaks may correspond to different low density structures.