Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 43: Poster Session II - MA 141/144 (Surface Spectroscopy on Kondo Systems; Frontiers of Surface Sensitive Electron Microscopy; Methods: Scanning Probe Techniques+Electronic Structure Theory+Other; Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation; joined by SYNF posters)

O 43.39: Poster

Dienstag, 26. Februar 2008, 18:30–19:30, Poster F

Transient surface temperature of ultralthin Bi(111) heterolayers on Si(001) upon fs-laser excitation — •Anja Hanisch, Boris Krenzer, Simone Möllenbeck, Tobias Pelka, Paul Schneider, and Michael Horn-von Hoegen — Department of Physics, Universität Duisburg-Essen, D- 47048 Duisburg, Germany

The transient temperature rise of ultrathin epitaxial Bi(111) films on Si(001) substrates upon excitation with fs-laser pulses is studied by ultrafast time resolved reflection high energy electron diffraction (RHEED). Spot intensities taken at different time delays between pumping laser pulses and probing electron pulses are converted to the transient surface temperature using the Debye-Waller Effect.[1]

A rapid increase of the surface temperature from 80 K up to 190 K is followed by a slow exponential decay with a time constant of 640 ps for a 5.5 nm thin Bi film.[2] The slow cooling is determined by the thermal boundary resistance at the interface between Bi and Si. We observe a linear dependence of the decay constant with the film thickness for films thicker than 6 nm, which is in agreement with the general theory of the thermal boundary resistance. In contrast films thinner than 6nm show an enhanced thermal boundary resistance with a decay constant up to two times larger than expected. In order to explain this deviation, we suggest that for thinner films the discretisation of the phonon dispersion compared to the bulk-like behaviour of thicker films plays an important role.

[1] A. Janzen et al., Rev. Sci. Inst. 78, 013906 (2007).

[2] B. Krenzer et al., New J. Phys. 8, 190 (2006).