# Regensburg 2019 – wissenschaftliches Programm

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# O: Fachverband Oberflächenphysik

## O 63: Poster Wednesday: Ultrafast Processes

### O 63.8: Poster

### Mittwoch, 3. April 2019, 17:45–20:00, Poster B1

**Electron-Phonon coupling in non-equilibrium: tr-RHEED on few monolayer Pb/Si(111) films** — •Tobias Witte, Bernd Hafke, Christian Brand, and Michael Horn-von Hoegen — Universität Duisburg-Essen, Lotharstr. 1, 47048 Duisburg, Germany

The recent advances in temporal resolution of electron diffraction experiments raised a multitude of questions regarding non-equilibrium dynamics of optically excited systems.
Here, the response of the phonon system of few monolayer (ML) thin Pb/Si(111) films upon fs-IR laser excitation is investigated. This system is known for exhibiting different quantum well states for even or odd layers which should influence the electron phonon interaction.
Employing time-resolved reflection high-energy electron diffraction the mean squared displacement of the surface atoms is analyzed for different Pb film thicknesses θ_{Pb}. The excitation time constant is found to be almost independent of the layer thickness for coverages of 3 ML ≤ θ_{Pb} ≤ 15 ML. The average value of τ_{exc} = 3.2 ± 0.4 ps is significantly slower than expected from a two temperature model (τ_{TTM} < 1 ps). This discrepency is discussed with respect to the non-thermal lattice model^{[1]}.

[1] L. Waldecker et al. - Phys. Rev. X 6, 021003 (2016)