Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 69: Metal Substrates: Clean Surfaces
O 69.1: Vortrag
Freitag, 30. März 2007, 10:15–10:30, H41
First-principles based prediction of composition and substitutional ordering in the Pt25Rh75(100) surface — •Philipp Welker, Ole Wieckhorst, and Stefan Müller — Universität Erlangen-Nürnberg, Lehrstuhl für Festkörperphysik, Staudtstr. 7, D-91058 Erlangen, Germany
The clean (100) surface of the disordered Pt25Rh75 alloy shows a strong tendency towards Pt segregation. Whereas the segregation profile is well known from both, STM- and LEED-investigations [1,2], only little progress has been made in understanding the energetics that lie behind the observed segregation behaviour.
We find almost the same Pt enrichment in the first layer as already predicted for the (111) surface [3]. This result can be explained in terms of the difference in surface energies of the two components, being almost the same for both the (111) and the (100) surface. However, the underlying layers in the (100) surface consist mainly of Rh, in contrast to the (111)-surface that shows an oscillatory depth profile. The difference in the layer dependent Pt concentration can be explained by the segregation energies, i.e. the energy gain for the exchange of a Pt atom from the bulk with a Rh atom from the surface.
Moreover, the combination of density functional theory (DFT) and cluster expansions with Monte-Carlo-simulations allows for the prediction of the temperature dependence of the substitutional ordering behaviour in the Pt25Rh75(100) surface.
[1] E. Platzgummer et al., Surf. Sci. 419 (1999) 236.
E. L. D. Hebenstreit et al., Surf. Sci. 441 (1999) 441.
S. Müller et al., Appl. Phys. A 82 (2006) 415.