The Interaction of Cobalt with CeO2(111) Prepared on Cu(111)

The interaction of cobalt with an ultrathiri CeO2(111) film on Cu(111) was studied by low energy ion scattering spectroscopy and X-ray photoelectron spectroscopy. At room temperature, Co grows three-dimensionally on the ceria film. For small Co coverages (0.2 ML), oxidation to Co2+ occurs together with the formation Of Ce3+ in the ceria. At higher Co coverages (07 and 2 ML), an increasing fraction of Co remained Metallic after deposition. Annealing to higher temperatures induced diffusion of Co2+ ions into the ceria film, and for metallic Co, presumably agglomeration occurs. At T >= 800 K, oxidation of significant amounts of Co-0 to Co2+ is found, along with diffusion, into the ceria. film, and partly also in the copper crystal underneath. On a reduced CeOx surface, the redox reaction between cobalt and cerium was hindered, which, in turn, slowed down cobalt migration into the ceria film.