Dresden 2011 – scientific programme

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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 36.104: Poster

Tuesday, March 15, 2011, 18:30–22:00, P4

Coupling of Pb adsorbate vibrations to Si(111) substrate studied by molecular dynamics — Sung Sakong, •Peter Kratzer, Simone Möllenbeck, Annika Kalus, Anja Hanisch-Blicharski, Martin Kammler, and Michael Horn-von Hoegen — Fakultät für Physik and Center for Nanointegration (CeNIDE), Universität Duisburg-Essen, Duisburg, Germany

The decay of low-lying vibrational modes of heavy adsorbates is best studied in the time domain. Time-resolved electron diffraction (RHEED) experiments provide evidence for a long (several ns) and a short (100 ps) time scale in the dissipation of vibrational energy of a Pb monolayer following pulsed laser irradiation. We perform density functional (DFT) calculations of a Pb/Si(111) (√3 × √3) surface to obtain the vibrational modes. To study the vibrational dynamics on the ns time scale, we use classical molecular dynamics with a Pb-Si interaction potential that matches the DFT data. The lattice dynamics at T=100K is simulated using a large super cell with 12 nm in depth, and the lower part of the Si slab is coupled to a thermostat. As initial condition, we assume that the energy deposited by the laser has already been converted to kinetic energy of the Pb atoms. We watch how this extra kinetic energy is dissipated into the Si substrate. After averaging over many trajectories, the relaxation dynamics monitored by the mean-square displacements of the Pb adatoms can be compared to the experimental data. In conclusion, we assign the experimentally observed short time scale to the decay of the "optical" Pb–Si mode, i.e., the Pb vibration relative to the top-most Si layer.