Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 55: Poster Session III - MA 141/144 (Methods: Atomic and Electronic Structure; Particles and Clusters; Heterogeneous Catalysis; Semiconductor Substrates: Epitaxy and Growth+Adsorption+Clean Surfaces+Solid-Liquid Interfaces; Oxides and Insulators: Solid-Liquid Interfaces+Epitaxy and Growth; Phase Transitions; Metal Substrates: Adsorption of Inorganic Molecules+Epitaxy and Growth; Surface Chemical Reactions; Bimetallic Nanosystems: Tuning Physical and Chemical Properties; Oxides and insulators: Adsorption; Organic, polymeric, biomolecular films; etc.)
O 55.60: Poster
Mittwoch, 27. Februar 2008, 18:30–19:30, Poster F
The PtxRu1−x/Ru(0001) surface alloy formation process studied by STM — •Andreas Bergbreiter, Harry E. Hoster, and R. Jürgen Behm — Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany
PtxRu1−x/Ru(0001) surface alloys were prepared by vapor deposition of Pt on a Ru(0001) single crystal, followed by annealing to 1350 K. According to high resolution STM analyses with chemical contrast, the composition of the PtxRu1−x/Ru(0001) surface is homogeneous on both nanometer and micrometer length scale. For x<0.8, the amount of Pt exactly matches the initial coverage by pseudomorphic Pt islands. Even after alloy formation we find islands on the surface. These islands are more compact in shape and larger in size than the initial Pt islands, but have the same Pt:Ru ratio as the surrounding terraces. Together with the homogeneous composition, the conserved amount of Pt surface atoms means, that virtually no Pt is buried below these alloy islands. Pt deposition at high temperatures and Ru overgrowth of Pt islands show that the absence of Pt in the subsurface layer (below the islands) can be rationalized by a preference of both Pt and Ru to occupy Ru 3-fold sites. High exchange rates between Pt (Ru) adatoms and atoms in the underlying layer allow equilibration of the topmost layers. The site preferences fit well to effective pair interaction energies derived from lateral atomic distribution within the PtxRu1−x/Ru(0001) surface alloys.