Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Poster Session I (Nanostructures at Surfaces; Metal Substrates: Epitaxy and Growth; Methods: Scanning Probe Techniques; Phase Transitions)
O 17.68: Poster
Montag, 26. März 2007, 17:30–20:30, Poster C
Time-resolved two-photon photoemission study of C60 — Benjamin Göhler, •Arne Rosenfeldt, and Helmut Zacharias — Physikalisches Institut, Westfälische Wilhelms-Universität, 48149 Münster, Deutschland
Ordered films of C60 with different thicknesses between 10 and 200 ML are evaporated onto Cu(111) and cooled down to 130 K. Using four-wave mixing in Xenon photons with 8.27 eV (150 nm) are generated. They have sufficient energy to probe low lying and occupied states and are used to check the preparation. Photons with 5.88 eV have sufficient energy to probe the excitons. Photons with 4.71 eV have sufficient energy to probe half of the LUMO, the LUMO+1, and the LUMO+2.
Two-photon photoemission is employed to populate intermediate states and probe their dynamics. The excitation probability of these states is measured as a function of photon energy. Time-resolved measurements are performed with both a Q-switched laser delivering 2.33 eV pulses with 150 ns duration and 3.50 eV pulses with 100 ns duration, and a mode-locked laser tunable between 2.35 and 5.88 eV with 75 ps pulse duration. A rate equation fitted to the electron dynamics suggests a lifetime of about 126 ps for the LUMO, 1 ns for the singlet exciton, (21 ± 3 ) µ s for the triplet exciton, and shorter lifetimes for LUMO+1 and LUMO+2. Pumping with 2.3 eV the result depends on pulse energy and pulse length.
The project is financially supported by the DFG in the SPP1093 “Dynamik von Elektronentransferprozessen an Grenzflächen”.