Berlin 2012 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 15: Heterogeneous catalysis I

O 15.11: Vortrag

Montag, 26. März 2012, 18:30–18:45, MA 042

Structural Investigation of the (7×√3)rect Oxygen Phase on Ag(111) — •Martin Ehrensperger¹, Miguel À. Niño², Tevfik O. Menteş², Andrea Locatelli², Sebastian Böcklein¹, Wolfgang Moritz¹, Sebastian Günther³, and Joost Wintterlin¹ — ¹Ludwig-Maximilians-Universität München, Germany — ²Sincrotrone Trieste S.C.p.A., Italy — ³Technische Universität München, Germany

We have investigated the structure of the (7×√3)rect oxygen phase on the Ag(111) surface by means of a low-energy electron diffraction (LEED)-I/V analysis. Further techniques were scanning tunneling microscopy, x-ray photoelectron spectroscopy (XPS), and low-energy electron microscopy. Three rotational domains are observed on a completely covered substrate surface. The symmetry is Pm with a mirror plane parallel to the <112> substrate directions. According to XPS the structure contains about one monolayer of an oxygen species that is closely related to the so-called "electrophilic" oxygen. Following the literature this oxygen species is the active species for the partial oxidation of ethylene to give ethylene oxide over Ag catalysts. Structures were tested containing adsorbed O atoms on the unchanged Ag(111) surface, possible reconstructions of the surface, surface oxide type structures and structures derived from bulk silver oxides. Relative integral intensities suggest a thickness of at least two layers of Ag atoms. All models deduced from variations of known structures of the entire Ag-O system or comparable surface oxygen systems of other metals can be excluded.