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 Wurth¹ — ¹Institut 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.