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O: Fachverband Oberflächenphysik

O 51: Metal Substrates: Adsorption III

O 51.3: Vortrag

Donnerstag, 29. März 2007, 11:45–12:00, H39

In-situ x-ray investigation on the oxidation of platinum (111) surfaces — •Claus Ellinger, Nikolai Kasper, Andreas Stierle, and Helmut Dosch — Max-Planck-Institut für Metallforschung,

We determined the oxide structure on the Pt(111) surface using surface x-ray diffraction. Platinum is one of the most important catalysts for the oxidation of carbonmonooxide and hydrocarbons and is also used as protecting coating material in highly reactive environments. For the understanding of these technological processes a detailed knowledge of Pt oxidation is essential. A important role in the high reactivity of Pt surfaces is attributed to existence of oxide structure phases. At 250 ^∘C and an O₂ pressure of 500 mbar we observe the formation of an oxide similar to α-PtO₂. The determined structure is described by a thin bulk oxide like film consisting of two layers of oxidized platinum. We find that the hexagonal unit cell of the oxide and the Pt(111) are aligned parallel which is in contrast to recent DFT calculations [1]. In addition, specular in-situ reflectivity measurements were carried out during the oxidation of a 100 Å thin Pt(111) film on a sapphire substrate. We demonstrate that an oxide is formed on the platinum film at 300 ^∘C and oxygen pressures from 100 mbar to 500 mbar. Furthermore a material loss during the reaction with oxygen was observed as macroscopic holes appeared locally in the Pt film at an O₂ pressure of 150 mbar and a temperature of 450 ^∘C.

[1] W.X. Li and B. Hammer, Chem Phys Lett 409, 1-7 (2005).