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O: Fachverband Oberflächenphysik

O 45: Metal Substrates II

O 45.7: Vortrag

Mittwoch, 13. März 2013, 12:00–12:15, H42

Kinetic vs. thermodynamic limitations of the formation of PtCu submonolayer alloys on Ru(0001) single crystals. — •Albert K. Engstfeld, Christoph K. Jung, and R. Jürgen Behm — Ulm University, Institute of Surface Chemistry and Catalysis, D-89069 Ulm, Germany

Core shell particles consisting of a metal A rich shell and a bi- or multialloy core, show a catalytic activity which may strongly differ from that of the pure metal particles. An interesting example are Pt enclosed alloy particles containing Cu, Co and Pt, which were found to be much more active to-wards O2 electroreduction than pure Pt. In this work we focus on the formation of Pt and Cu submonolayer alloys on Ru(0001), which represents the core for a core shell model catalyst. The surfaces have been investigated under ultra high vacuum conditions, using scanning tunneling microscopy (STM), to reveal the surface morphology as well as the atom distribution within the surface alloy. The limitation in the preparation of the surface alloy is the temperature, since at 750 K Pt starts intermixing with the Ru(0001) substrate. Just below this temperature, the intermixing of Cu and Pt on the surface is however kinetically hindered, which leads to coexistent mixed and unmixed 2D phases of both metals. Optimizing the experimental conditions (e.g. evaporation sequence, temperature ...), we are able to prepare short-range ordered monolayer surface alloys covering the entire surface over the full concentration regime (0-100%), The distribution of surface atoms in the monolayer surface alloys will be discussed based on the Warren Cowley short-range order parameters.