Dresden 2014 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 82: Metal Substrates II
O 82.8: Vortrag
Donnerstag, 3. April 2014, 17:45–18:00, WIL A317
Au-Ag(110) Alloy Surfaces: Surface Restructuring and Oxygen Chemistry — •Martin Schmid, Joshua Klobas, Robert J. Madix, and Cynthia M. Friend — Department of Chemistry and Chemical Biology, Harvard University, Cambridge MA, USA
We investigated the morphology and oxygen chemistry of thin film Au-Ag(110) alloy surfaces. The alloys were prepared by deposition of Au onto an Ag(110) single crystal under UHV conditions. The initial deposition was followed by several steps of moderate annealing in order to fabricate a thin, homogeneous surface alloy. Examination of the Au-Ag(110) surfaces with Scanning Tunneling Microscopy (STM) showed a substantial surface restructuring on the submicrometer scale, which is associated with the onset of gold diffusion into the Ag(110) bulk, starting at 400K. After repeated moderate annealing steps to 630K, an apparently constant thin film composition could be established, as confirmed with angle resolved X-ray Photoelectron Spectroscopy (XPS). The oxygen chemistry of the thin film alloys was monitored with Temperature Programmed Desorption (TPD) experiments. Exposing the thin film alloys to O2 (pressure range of 1x10−6 mbar) showed a linear dependence between the oxygen uptake of the thin film at 300K and its gold content. Furthermore, probing the adsorption sites of chemisorbed O2 at low temperatures (125K) showed strong indications that gold atoms, while being unreactive themselves, control the oxygen uptake by shaping the size, amount, and distribution of reactive Ag sites.