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O: Oberflächenphysik

O 14: Struktur und Dynamik reiner Oberfl
ächen

O 14.1: Vortrag

Freitag, 4. März 2005, 15:45–16:00, TU EB407

Time-resolved low energy electron diffraction from large molecules on surfaces — •Claudio Cirelli^1,2, Matthias Hengsberger¹, Andrei Dolocan¹, Hansjörg Neff¹, Jürg Osterwalder¹, Herbert Over², and Thomas Greber¹ — ¹Physik-Institut, Universität Zürich, CH-8057, Switzerland — ²Physikalisch-Chemisches Institut, Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 Gießen, Germany

In order to observe dynamics of molecules adsorbed on solid surfaces in real time, it is necessary to develop a technique which combines both temporal and spacial resolution on the scale of molecular motion. This task is tackled with a pump-probe experiment, where Low Energy Electron Diffraction (LEED) probes the collective response of a surface on a laser pump pulse as a function of time delay between pump and probe. We present an electron gun that produces ultra-short electron pulses by two-photon photoemission process when 400nm laser light pulses are focused onto a gold cathode (20nm thick film deposited on sapphire substrate): the electron yield is about 0.5 electron/pulse with 0.5nJ laser pulses with a measured energy resolution of 0.7eV at 100eV. This results in a nominal time resolution of 3ps. As a molecular system we investigate one monolayer of C₆₀ on Ag(111), that forms a 2√3x2√3 R30^∘ structure. This system has a low Debye temperature of about 50K and is thus, together with the large mass of C₆₀, well suited for our purpose. First results will be presented and compared to results of static LEED experiments.