Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 35: Poster Session II (Polymeric biomolecular films; Nanostructures; Electronic structure; Spin-orbit interaction; Phase transitions; Surface chemical reactions; Heterogeneous catalysis; Particles and clusters; Surface magnetism; Electron and spin dynamics; Surface dynamics; Methods; Electronic structure theory; Functional molecules)
O 35.81: Poster
Dienstag, 27. März 2012, 18:15–21:45, Poster B
Two-photon photoemission from Si(111) 7×7 — •Jens Güdde, Andreas Damm, Marcel Reutzel, Alexander Lerch, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg
The dynamics of photoexcited electrons in unoccupied states of the Si(111) 7×7 surface has been investigated by time- and angle-resolved two-photon photoemission (2PPE) for different sample temperatures. Aside from non-resonant 2PPE from the occupied S2 surface band and the valence band maximum we observe the population dynamics in the initially filled (S1) and and empty (U1) surface bands as well as in the X valley of Si close to the surface. The population in the conduction band (CB) shows a temperature-dependent delayed rise on the same time scale of several hundred femtoseconds as the electron thermalization in the U1 band. The photoemission from the S1/U1 as well as from the CB is completely quenched by hydrogen adsorption. Together with the delayed population rise, this suggests that the CB is populated by electrons which were initially excited in the U1 band. The investigation of the population dynamics for different parallel momenta along the Γ-K-direction reveals that the intraband relaxation within the CB proceeds on a time scale of few picoseconds while the population at the conduction band minimum decays with a time constant of several tens of picoseconds.