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

The interaction of cobalt with an ultrathin 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 (0.7 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 Co0to Co2+is found, along with diffusion into the ceria film, and partly also in the copper crystal underneath. On a reduced CeOxsurface, the redox reaction between cobalt and cerium was hindered, which, in turn, slowed down cobalt migration into the ceria film.