Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 40: Adsorption an Oberfl
ächen IV

O 40.2: Talk

Tuesday, March 8, 2005, 11:00–11:15, TU EB202

Alloy surface segregation in reactive environments via density-functional theory and atomistic thermodynamics — •John Kitchin, Karsten Reuter, and Matthias Scheffler — Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin

The chemical and materials properties of an alloy surface depend sensitively on its detailed surface composition and structure, which in turn can differ substantially from the one of the bulk alloy due to segregation of one species to the surface. Concerning the alloy function e.g. in catalytic or corrosive environments, this surface segregation can furthermore depend on the partial pressures and temperatures in the surrounding, if one alloy component interacts more strongly with a gas-phase species than the other. Instead of solely predicting the chemical and materials properties on the basis of the formal bulk composition, this requires a theory that explicitly considers the effect of the reactive environment.
As a first step in this endeavor, we are extending the concepts of ab initio atomistic thermodynamics to address segregation in binary transition metal alloys in the presence of a reactive gas phase. We apply the approach to the (111) surface of Ag₃Pd in an O₂ atmosphere, and find that contrary to the situation in ultra-high vacuum, Pd segregates to the surface at high oxygen pressures. We discuss the difficulties and possible inaccuracies of the ab initio atomistic thermodynamic approach with respect to the limited exploration of configuration space and the steps necessary to proceed beyond it.