Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 89: Metal Substrates: Epitaxy and Growth
O 89.8: Vortrag
Freitag, 29. Februar 2008, 11:15–11:30, MA 041
Atomic ensembles in AuxPt1−x/Pt(111) surface alloys - linking a quantitative STM study with DFT calculations — •Andreas Bergbreiter1, Harry E. Hoster1, Yoshihiro Gohda2, Axel Groß2, and R. Jürgen Behm1 — 1Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany — 2Institute for Theoretical Chemistry, Ulm University; D-89069 Ulm, Germany
The knowledge of the available adsorption sites on catalyst surfaces is essential for the understanding of their adsorption and catalytic properties. 2D alloys, in which intermixing is confined to the surface, are excellent model systems to study correlations between the atomic distribution and the adsorption or reaction behavior. Based on high-resolution STM imaging with chemical contrast, the atomic distribution in AuxPt1−x/Pt(111) surface alloys is characterized by a segregation into homoatomic aggregates. This can be rationalized by an effective repulsion between unlike atoms in the outermost layer, which is supported also by DFT calculations. Using a 2D lattice gas Hamiltonian, we are able to simulate the atomic distribution via a Metropolis Monte-Carlo (MC) algorithm [1]. The effective interaction parameters for the Hamiltonian were derived from DFT-calculated energies for different ordered AuxPt1−x/Pt(111) slabs. The measured surface densities of different atomic ensembles, as counted in the STM data, and the MC generated distribution agree well, even though only pairwise interactions are considered in the Hamiltonian.
[1] A. Bergbreiter et al.; Phys. Chem. Chem. Phys. 9, 2007; 5127.