Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 71: Metal substrates: Epitaxy and growth
O 71.10: Vortrag
Donnerstag, 25. März 2010, 17:15–17:30, H31
Adsorbate-induced segregation of C/Pt25Rh75(100): ab-initio predictions — •Tobias Kerscher, Wolfgang Landgraf, and Stefan Müller — Universität Erlangen-Nürnberg, Lehrstuhl für Theoretische Physik 2, Staudtstr. 7, 91058 Erlangen, Germany
The segregation profile of alloy surfaces can strongly depend on the presence of adsorbates, a fact that is especially interesting for catalysts.
The (100) surface of the alloy Pt25Rh75 provides an example:
For the clean surface, the experiment [1] shows a strong Pt enrichment in the top atomic layer and a depletion underneath.
Yet, even a small amount of carbon impurity (8% of a monolayer) leads to a considerable decrease in the Pt top layer concentration [1].
We use an ab-initio-based cluster-expansion in the framework of the UNCLE code [3] to efficiently model this adsorbate-induced change in segregation.
The properties of the system are found to be controlled by two competing effects:
the different segregation energies of Pt and Rh, and their individual binding energies to C.
We discuss the substitutional ordering of the system as a function of C-coverage.
Supported by Deutsche Forschungsgemeinschaft
[1] E. Platzgummer et al., Surf. Sci. 419 (1999), 236
[2] S. Müller, M. Stöhr, O. Wieckhorst, Appl. Phys. A. 82 (2006), 415
[3] D. Lerch et al, Modelling Simul. Mater. Sci. Eng. 17 (2009), 055003