Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)

O 15.79: Poster

Freitag, 4. März 2005, 17:00–20:00, Poster TU D

Time-Resolved Reflection High-Energy Electron Diffraction – Pump-Probe Experiments on Clean and Bi-covered Si Surfaces — •A. Janzen, B. Krenzer, and M. Horn-von Hoegen — Universität Duisburg-Essen, Institut für Experimentelle Physik, 45117 Essen

Time-resolved Reflection High-Energy Electron Diffraction opens a new pathway to investigate the structural dynamics at surfaces subsequent to an intense electronic excitation by a fs-laser pulse. By variation of the time delay between a fs-laser-pump pulse and a ps-electron-probe pulse the transient state of the surface under examination can be determined. The construction of a laser-driven electron gun providing picosecond electron pulses and the setup of an electron diffraction apparatus has already been successfully accomplished.

We are now conducting studies of ultrafast heating phenomena after laser excitation of clean Si surfaces and thick Bi-films epitaxially grown on Si. The last step in the chain of processes following the excitation is the transient heating of the lattice, leading to a drop in the diffraction spot intensity (Debye-Waller effect). Since Bi has a much lower Debye temperature than Si, Θ_{D, Bi}=119 K compared to Θ_{D, Si}=652 K, the Debye-Waller effect is much more pronounced on Bi surfaces than on Si surfaces. First results of the pump-probe experiments and a discussion of the encountered problems will be presented.