Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 62: Metal Substrates: Adsorption of Inorganic Molecules

O 62.9: Talk

Thursday, February 28, 2008, 11:30–11:45, MA 042

Monte-Carlo lattice gas simulation of the thermal desorption behavior of CO from Pt_xAu_1−x/Pt(111) surface alloys — •Harry E. Hoster¹, Yoshihiro Gohda², Andreas Bergbreiter¹, Menhild Eyrich¹, Joachim Bansmann¹, Axel Groß², and R. Jürgen Behm¹ — ¹Institute of Surface Chemistry and Catalysis, Ulm University, 89069 Ulm, Germany — ²Institute of Theoretical Chemistry, Ulm University, 89069 Ulm, Germany

The thermal desorption behavior of CO adsorbed on Pt_xAu_1−x/Pt(111) surface alloys was studied by Monte Carlo simulations in a lattice gas approximation [1,2], comparing different Pt:Au ratios and initial CO_ad coverages. Based on thermal desorption data and DFT calculations, the CO molecules preferentially occupy Pt on-top sites of Pt_xAu_1−x/Pt(111) surface alloys, and the adsorption energies are approximately constant for different numbers of neighboring Au atoms (ligands). Au sites are not occupied at room temperature. The atomic distribution in the surface layer used in the simulations was derived from STM data with chemical contrast, and the adsorption energies stem from DFT calculations. At higher CO_ad-coverages, the CO-CO repulsions are considered via a pair interaction parameter determined by fitting to the experimental data. The accuracy of the lattice gas approach for inhomogeneous surfaces is discussed by comparing with the experimental thermal desorption data.

[1] J.L.Sales, G.Zgrablich, V.P.Zhdanov, Surf.Sci 209(1989)208

[2] V.P.Zhdanov, J.L.Sales, R.O.Unac, Surf.Sci.Lett.381(1997)L599