SURFACE MODIFICATION OF COPPER DUE TO COADSORBED OXYGEN AND CADMIUM PROBED WITH OPTICAL 2ND-HARMONIC GENERATION

Oxygen adsorbates are unavoidable on Cu in an aqueous environment. In this work, such a polycrystalline Cu surface is decorated with electro deposited Cd. Optical second harmonic generation is used to probe the time resolved kinetics of co-adsorbed oxygen and Cd on this electrode. The optical data contain contributions from the linear dielectric fun ctions, and second order susceptibility elements of the electrochemica l interface. A phenomenological theory is presented to resolve the con tributions of these optical parameters in the optical signal of the Cu surface. Electronic effects of the co-deposited oxygen and Cd on Cu a re analyzed by testing the coverage dependent features of the interfac ial optical parameters. Numerical calculations are performed for this analysis. The results are characterized in terms of a Cd-induced lower ing of the surface work function of Cu. The results also demonstrate h ow second harmonic generation can be used to analyze the relatively co mplicated electrochemistry of Cu. (C) 1998 Elsevier Science Ltd. All r ights reserved.