Berlin 2005 – wissenschaftliches Programm
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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 Cirelli1,2, 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.