Dresden 2006 – scientific programme
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O: Oberflächenphysik
O 24: Adsorption III
O 24.4: Talk
Tuesday, March 28, 2006, 16:30–16:45, TRE Phys
High-Pressure Oxidation of Pd(111) Single Crystal Surface: In-situ X-ray Diffraction studies — •Nikolai Kasper, A. Stierle, P. Nolte, and H. Dosch — Max - Planck-Institut für Metallforschung, Heisenbergstr. 3, D 70569 Stuttgart, Germany
The interaction of molecular oxygen with a Pd(111) single crystal surface has been studied in a wide temperature and pressure range (30 - 800 ∘ ∘C and 10−10 mbar - 1 bar, respectively). The stability regions of the surface oxide Pd5O4 and the bulk PdO have been obtained. Independent on the oxygen partial pressure, only chemisorbed oxygen layers form below 300 ∘C. The Pd5O4 surface oxide exhibits rather narrow stability (p, T) region - it can be formed only at temperatures 300 ∘ ≤ T ≤ 650 ∘C. Increasing pressure induces the transformation of the surface oxide into the PdO bulk oxide. The formation of unstable Pd5O4 structure has been observed during the decomposition of bulk oxide. The chemisorbed oxygen layers transform directly into the bulk PdO at the temperatures above 650 ∘C. From comparison of the stability diagram with the results of DFT-calculations one can easy see the effect of kinetic hindrance in formation of both surface and bulk oxides at low temperatures (300 ∘ ≤ T < 450 ∘C), similar to the case of Pd(100) oxidation [1]. The crystal srtucture of Pd5O4 obtained from crystal truncation rod measurements agrees with the literature data [2].
Financial support of this work is acknowledged from the European Union under contract no. NMP3-CT-2003-505670 (NANO2).
[1] E. Lundgren et al., Phys. Rev. Lett., 88, 246103 (2002)
[2] E. Lundgren et al., Phys. Rev. Lett., 92, 046101 (2004)