Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 75: Oxides and Insulators: Epitaxy and Growth
O 75.4: Vortrag
Donnerstag, 28. Februar 2008, 16:00–16:15, MA 042
Growth and characterization of ultrathin CeOx films on Pt(111) — Jan Markus Essen, Tobias Pertram, •Conrad Becker, and Klaus Wandelt — Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, 53115 Bonn, Germany
The use of cerium oxides in catalysis is mainly motivated by its good redox properties and oxygen storage capability. The reproducible preparation of well characterized thin films of CeOx on a conducting material is important for using these films as model catalyst for the investigation of simple reactions with surface sensitive techniques. In this study we investigated CeOx films grown on Pt(111) with CO-TPD and HREELS.In order to produce CeOx thin films we followed three different routes: 1) Oxidation of Pt-Ce surface alloys at different temperatures; 2) oxidation of pure vapor deposited Ce films on Pt(111); and 3) evaporation of Ce in an oxygen atmosphere followed by annealing in oxygen. For Pt-Ce surface alloys oxidized at 900 K HREELS shows a pure CeO2 film composition. Oxidation at 700 K and 1000 K however, does not lead to full oxidation of Ce, but a mixed oxide is suggested by the phonon spectra. CO-TPD measurements show that the pure CeO2 films on Pt(111) are not closed. In contrast, exposing the Ce-covered Pt(111) surface to oxygen at 90 K followed by annealing to 1000 K does generate a fully covered surface, but again with a mixed oxide. Evaporating Ce in oxygen atmosphere also produces fully oxidized CeO2 films but they show no good long-range order.