Morphology and defect structure of the CeO2(111) films grown on Ru(0001) as studied by scanning tunneling microscopy

The morphology of ceria films grown on a Ru(0001) substrate was studied by scanning tunneling microscopy in combination with low-energy electron diffraction and Auger electron spectroscopy. The preparation conditions were determined for the growth of nm-thick, well-ordered CeO2(111) films covering the entire surface. The recipe has been adopted from the one suggested by Mullins et al. [DR. Mullins, P.V. Radulovic, S.H. Overbury, Surf. Sci. 429 (1999) 186] and modified in that significantly higher oxidation temperatures are required to form atomically flat terraces, up to 500 angstrom in width, with a low density of the point defects assigned to oxygen vacancies. The terraces often consist of several rotational domains. A circular shape of terraces suggest a large variety of undercoordinated sites at the step edges which preferentially nucleate gold particles deposited onto these films. The results show that reactivity studies over ceria and metal/ceria surfaces should be complemented with STM studies, which provide direct information on the film morphology and surface defects, which are usually considered as active sites for catalysis over ceria. (c) 2006 Elsevier B.V. All rights reserved.