C. Mansilla, F. Yubero, M. Zier, R. Reiche, S. Oswald, J.P. Holgado, J.P. Espinós, A.R. González-Elipe
Surface and Interface Analysis, 38 (2006) 510-513
doi: 10.1002/sia.2269

We have studied the first nucleation steps and the chemical interactions of small amounts of cerium oxide deposited on two surfaces with different chemical nature, alumina and a partially reduced titania. Cerium oxide was deposited by electron bombardment of CeO₂ pellets in ultra-high vacuum conditions. All experiments were done in situ in order to avoid contamination related to exposure to air. The relative amounts of Ce³⁺ and Ce⁴⁺ species present at the successive deposition steps have been quantified. It is found that for initial steps of deposition, high amounts of Ce³⁺ are stabilised at the CeO_x/TiO_x interface, while an approximately even mixture of Ce³⁺ and Ce⁴⁺species appear at the CeO_x/Al₂O₃ interface. Thicker deposits are characterised by the presence of only Ce⁴⁺ species independently of the substrate. It is found that cerium oxide grows in the form of islands on both substrates. These islands are taller in the case of deposition on reduced titania than on alumina. This result is confirmed by both angle resolved X-ray photoelectron spectroscopy (XPS) and inelastic XPS peak shape analysis. The correlation between the growing microstructure and the chemical interaction at the interfaces is discussed.