Cerium oxide films on TiOxcoated Pt(111)-single crystals

The epitaxial growth of thin and continuous CeO2(111) films on metal surfaces suffers from the preferential formation of a 3D-like morphology, even though epitaxial relationships exist with the substrate lattices. This holds for films prepared by reactive evaporation of Ce in O2 on Pd(111) and Rh(111), or by oxidation of an ordered surface alloy Pt5Ce/Pt(111). One may expect a decreased lattice mismatch if metal surfaces are used that are coated with ultra thin and ordered oxide-based buffer layers. As a candidate we have chosen the ''wagon wheel'' phase of TiOx grown on a Pt(111) surface which reveal a hexagonal symmetry and an interatomic spacing of 3.26 A. This value is closed to the lattice constant of 3.86 A for CeO2(111). The film is 1.2 ML thick and shows a continuous morphology in STM. CeOx films are subsequently grown by thermal evaporation of cerium in O2 at RT. The films were analysed by LEED and XPS to determine the geometric structure, chemical composition and stoichiometry. First measurements reveal a change in the stoichiometry of the TiOx film that is discussed in terms of an interface reaction. Additional information on the initial stages of growth is obtained from STM