Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 31: Surface Chemical Reactions and Heterogeneous Catalysis I

O 31.7: Vortrag

Dienstag, 27. März 2007, 17:15–17:30, H38

(4x4)O structure on Ag(111): LEED-I/V analysis and high-pressure STM — •Robert Reichelt, Sebastian Günther, Joost Wintterlin, and Wolfgang Moritz — Ludwig-Maximilians-Universität, München, Germany

The (4x4)O structure on Ag(111) plays a central role in the Ag/O system, and it is assumed that structurally similar oxygen species contribute to the ethylene epoxidation on Ag surfaces. Several models of the (4x4)O structure on Ag(111) have been discussed in the past. We have performed a LEED-I/V (low-energy electron-diffraction) analysis using two different experimental setups. One was a conventional LEED system mounted into a laboratory UHV system, the second was a LEEM (low-energy electron microscope). The (4x4)O structure was prepared by exposure to NO2. The two data sets agree very well with each other, demonstrating that I/V structure analyses can be performed either with LEED or with LEEM. The structure obtained in the analysis confirms a recently proposed model that involves a reconstruction of the Ag(111) surface. Previous models based on a thin layer of Ag2O are disproved. The (4x4)O structure was also investigated by high-pressure STM in an attempt to study its role in the partial oxidation of ethylene. The formation of the (4x4)O structure could be monitored in situ, under oxygen pressures in the mbar regime and at elevated temperatures. When ethylene was added massive structure changes occurred, indicating that the (4x4)O structure is most likely not the active phase under reaction conditions.