Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 36: Structure and dynamics

O 36.3: Talk

Thursday, March 30, 2006, 11:45–12:00, WIL C207

Dynamics of Heat Transport in Ultrathin Bi-Films on Si(001) Studied by Ultrafast Electron Diffraction — •Andreas Janzen, Boris Krenzer, Ping Zhou, Dietrich von der Linde, and Michael Horn-von Hoegen — Universität Duisburg-Essen, Institut für Experimentelle Physik, 47057 Duisburg

We used Ultrafast Electron Diffraction to study the surface temperature evolution following the intense fs-laser excitation (800 nm, 45 fs, 1.3 mJ/cm²) of thin, epitaxial Bi(111)-films deposited onto Si(001)-substrates. Reflection high-energy electron diffraction patterns at 7 keV have been recorded in a laser pump-electron probe experiment with ps-time resolution. The transient surface temperature is determined utilizing the intensity drop due to the Debye-Waller effect and comparing the transient diffraction spot intensity with a static calibration measurement. The cooling of a 6 nm thick Bi-film is much slower (τ=640 ps) than expected for purely diffusive bulk-heat conduction. For the smooth, abrupt Bi/Si-interface, the acoustic mismatch model explains this effect in terms of total internal reflection of phonons at the interface: the phonons are trapped in the Bi-film. The dependence of the cooling rate on the Bi-film thickness and the transition to the regime of diffusive heat transport will also be addressed.