Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 36: Poster Session II (Metals; Nanostructures at surfaces; Surface or interface magnetism; Spin-Orbit Interaction at Surfaces; Electron and spin dynamics; Surface dynamics; Methods; Theory and computation of electronic structure)
O 36.105: Poster
Dienstag, 15. März 2011, 18:30–22:00, P4
Dynamics of the β(√3×√3) ↔ (3×3)-Pb/Si(111) phase transition on the ps-timescale — •Jörg Reimann, Tim Frigge, Simone Möllenbeck, Friedrich Klasing, Martin Kammler, and Michael Horn-von Hoegen — Department of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, D-47057 Duisburg, Germany
The structural dynamics of strongly driven phase transitions on surfaces take place on a picosecond timescale. Ultrafast time resolved electron diffraction in a RHEED (reflection high energy electron diffraction)-geometry is an excellent technique to study such processes after excitation by a fs laser pulse [1]. In a metallic adsorbat system absorption of the photons results in an excitation of the electron system. Electron-phonon coupling causes heating of the adsorbate layer and may trigger the phase transition. In order to study the dynamics of an order-disorder phase transition far away from thermal equilibrium we performed time resolved measurements on the β(√3×√3) ↔ (3×3)-Pb /Si(111) phase transition with Tc = 84∘C. The Pb adlayer is excited by a 50 fs laser pulse with 800 nm at a sample temperature of 25 K. After excitation the β(√3×√3)-diffraction spot intensity drops instantaneously due to the Debye Waller effect but is followed by a sharp increase which is delayed by 30 ps. While the intensity decrease is explained by thermal heating of the adsorbate layer up to 125 K, we attribute the increase of intensity to a delayed structural phase transition triggered by the temperature rise.
[1] A. Janzen et al., Surf. Sci. 600, 4094 (2006)