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O: Fachverband Oberflächenphysik

O 41: Poster Session I (Semiconductor Substrates: Epitaxy and growth; Semiconductor Substrates: Adsorbtion; Semiconductor Substrates: Solid-liquid interfaces; Semiconductor Substrates: Clean surfaces; Oxides and insulators: Epitaxy and growth; Oxides and insulators: Adsorption; Oxides and insulators: Clean surfaces; Organic, polymeric and biomolecular films - also with adsorbates; Organic electronics and photovoltaics, Surface chemical reactions; Heterogeneous catalysis; Phase transitions; Particles and clusters; Surface dynamics; Surface or interface magnetism; Electron and spin dynamics; Spin-Orbit Interaction at Surfaces; Electronic structure; Nanotribology; Solid/liquid interfaces; Graphene; Others)

O 41.63: Poster

Dienstag, 23. März 2010, 18:30–21:00, Poster B1

Ultra-Fast Time Resolved Electron Diffraction of Vibrational Dynamics in an Adsorbate Layer: (√3×√3) Pb on Si(111) — •Annika Kalus, Simone Möllenbeck, Paul Schneider, Anja Hanisch-Blicharski, Boris Krenzer, Martin Kammler, and Michael Horn-von Hoegen — Department of Physics and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47057 Duisburg, Germany

We use ultra-fast time resolved electron diffraction to analyze structural dynamics of adsorbates on surfaces on a ps-timescale upon excitation by fs-laser pulses. Surface sensitivity is obtained by a RHEED (reflection high energy electron diffraction)-geometry. Utilizing the Debye-Waller effect the damping of the vibrational amplitude of the adsorbate atoms could be followed as function of time in a pump probe set up. As an example we used the (√3×√3) Pb/Si(111) system which was prepared by deposition of Pb on Si(111) - (7×7) at 300 K followed by an annealing step to 500 K. As a result we obtained a Pb (√3×√3) reconstruction with a coverage of one monolayer and a small number of large Pb islands. After excitation we measure a relaxation time constant of the hot adsorbate system of 150 ps. This low cooling rate is explained by the huge difference in mass of Si and Pb atoms which prevents effective coupling of the Pb vibrational modes to the phonon bath in Si substrate.