Initial stages of oxidation at noble metal surfaces: The cases of Ag and Cu

The initial stages of oxide nucleation and surface oxide formation are hot topics at the moment due to the possible application of these materials in many fields of science and technology. The understanding of the parameters controlling these processes is therefore pivotal not only for the fundamental knowledge of the physical phenomenon but also for enabling the growth of better quality oxide phases, with a higher degree of order and/or a lower density of contaminants. Here I will summarize the main results obtained by a collaboration between experimental groups in Genova and Osaka and between the experimentalists in Genova and theoretical groups in Trieste and Ljubljana, on the initial oxidation of the noble metals Ag and Cu. I will show that the local morphology of surface defects and/or the dosing conditions are essential elements to determine the nature of the oxide form which starts to nucleate upon exposure to O2. On stepped Ag we find that, under vacuum conditions, the stoichiometry of the initial oxide nuclei is tuned by the atomic geometry at the low coordination site, while on Cu(410) the oxidation efficiency comes out to be highly enhanced both by the presence of steps and by exposure to hyperthermal oxygen. The relative amount of cuprous and cupric oxide formed depends on oxidation temperature.