Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 44: Metal Substrates: Structure, Epitaxy and Growth
O 44.6: Poster
Dienstag, 21. März 2017, 18:30–20:30, P1A
Silver segregation near oxygen chain structures on a gold-silver alloy surface: A cluster expansion study combined with ab initio MD simulations — •Sandra Hoppe1, Yong Li2, Lyudmila V. Moskaleva2, and Stefan Müller1 — 1Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany — 2Institute of Applied and Physical Chemistry and Center for Environmental Research, University of Bremen, Bremen, Germany
The high catalytic activity of nanoporous gold has been attributed to its residual silver content originating from the parent Ag-Au alloy. Therefore, the knowledge about the thermodynamically stable positions of silver atoms on the surface of nanoporous gold is crucial for understanding elementary stages of various catalytic processes, in particular, the chemical nature and adsorption properties of active oxygen species. In this study, we investigate the surface segregation of silver in the presence of atomic-oxygen adsorbates arranged in chains on the stepped and kinked Au(321) surface. Remarkably, we find that up to very high silver surface concentrations, the silver atoms do not occupy positions within the oxide chain, but prefer locations next to it. We identify two effects responsible for this behavior. First, gold is stabilized within the chain by partially covalent bonds with oxygen. Second, silver located in the vicinity of the chain binds stronger to oxygen than gold at the same position does. Ab initio molecular dynamics simulations support our conclusions and reveal that not only silver atoms but also the entire oxide chains may diffuse on the surface to maximize the binding contacts between adjacent silver and oxygen atoms.