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Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 30: Adsorption an Oberfl
ächen III

O 30.4: Talk

Monday, March 7, 2005, 11:30–11:45, TU EB301

Adsorption geometry of hexafluorobenzene on the Cu(111) surface: A polarization dependent NEXAFS study — •Sethuraman Vijayalakshmi1, Alexander Föhlisch1, Franz Hennies1, Annette Pietzsch1, Mitsuru Nagasono1, Patrick Kirchmann2, Martin Wolf2, and Wilfried Wurth11Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany — 2Department of Physics, FU Berlin, Arnimallee 14, 14195 Berlin

The orientation of hexafluorobenzene (C6F6) molecules adsorbed on the Cu(111) surface has been studied by C K-edge near edge x-ray absorption fine structure spectroscopy (NEXAFS) for different adsorbate coverages. Photoelectron spectroscopy and temperature programmed desorption studies indicate distinct multilayer, bilayer, monolayer and half a monolayer phases. NEXAFS on these different coverages shows that the π* absorption resonance has maximum intensity for the electric field vector perpendicular to the surface whereas it is substantially suppressed for the electric field vector in plane. Thus we propose that C6F6 molecules adsorb with the molecular plane parallel to the surface for all the investigated coverages. This observation differs from the adsorption of benzene where the molecules have random orientation in multilayers, interacting only through Van der Waals force. For C6F6 our results indicate a significant interaction between the C6F6 molecules leading to a preferential orientation in multilayers.
This work was supported by the Deutsche Forschungsgemeinschaft SPP1093.

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