Coverage-dependent behavior of ultrathin Cu films UHV and electrochemical studies

Submonolayer to monolayer coverages ofCu electrodeposited and vacuum-deposited onto a well-characterized Pt ( 11 I ) surface were studied in both ultrahigh vacuum (UHV) and electrochemical environments using a combined UHV-electrochemical apparatus. Substantial discrepancy was observed between the voltammetrically measured Faradaic charge and the theoretically expected value based on UHV determined Cu coverages. For Cu coverages > 0.5 monolayers (ML), Oc, u > 0.5, the Coulometrically determined Cu coverage was too low by up to 30%; for Ocu < 0.5, the Coulometrically determined Cu coverage was too high by up to 50%. A significant contribution to this discrepancy at O~,u > 0.5 is believed to be the partially charged nature of the Cu adlayers. For 0cu < 0.5 this discrepancy can be accounted for by the partial discharge of coadsorbed anions during the electrooxidative desorption of Cu.