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 θPb. The excitation time constant is found to be almost independent of the layer thickness for coverages of 3 ML ≤ θPb ≤ 15 ML. The average value of τexc = 3.2 ± 0.4 ps is significantly slower than expected from a two temperature model (τTTM < 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)

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