LAUSR

The growth, electronic structure and stability of Sm on ordered CeO2(111) thin films grown on Cu(111) were investigated by means of X-ray photoelectron spectroscopy (XPS), low energy electron diffraction, and scanning tunneling microscopy (STM). Metallic samarium was deposited on the CeO2(111) surface by thermal evaporation under ultrahigh vacuum conditions at room temperature. The XPS data suggest that metallic Sm is oxidized to Sm3+ upon the deposition of Sm on CeO2, accompanied by the reduction of Ce4+ to Ce3+. With increasing the Sm coverage, the concentration of Ce3+ increases monotonically. After depositing 6 ML of Sm, only Ce3+ is observed within the detection depth of XPS. The STM results indicate that Sm exhibits a two-dimensional growth on the CeO2(111) surface at low coverages. Annealing to higher temperatures leads to the agglomeration of Sm particles and concurrent diffusion of Sm into the ceria film. These results illustrate that Sm can modify both the electronic and structural properties of ceria.