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 36.98: Poster
Dienstag, 15. März 2011, 18:30–22:00, P4
Time resolved desorption of atomic hydrogen from graphite induced by femtosecond laser pulses — •Robert Frigge1, Tim Hoger1, Henrik Witte1, Thomas Olsen2, Jakob Schiotz2, and Helmut Zacharias1 — 1Physikalisches Institut, Universität Münster, Germany — 2CINF, Technical University of Denmark, Denmark
The desorption of hydrogen from graphite (HOPG) is an important issue in the understanding of molecular hydrogen formation on dust particles upon irradiation. The velocity distribution of atomic hydrogen from HOPG is examined after surface excitation with fs-laser pulses at λ = 400 nm. Desorbed neutral H atoms are ionized using (2+1) REMPI via the 2s ← 1s transition, and are detected with a time-of-flight mass spectrometer. As a result the velocity distribution reveals a structure consisting of different maxima for fast, medium and very slow desorbed hydrogen atoms. Electron scattering calculations have been performed employing a repulsive electronic excited state and H-graphite adsorption potentials corresponding to different adsorption sites [1]. Via populating diferent vibrationally excited intermediate states by multiple scattering events velocity distributions for desorption out of different adsorption sites are obtained. A good agreement with the experimentally observed velocities is obtained. A nonlinear fluence dependence for the fast electrons, allow two pulse-correlation experiments and as a result we derive a pulse-delay dependent yield with a FWHM of about 700 fs. This correlation time indicates short lifetimes of the excited electrons and supports a calculation in the DIMET model. [1]R. Frigge et al., Phy. Rev. Lett.,104, 256102 (2010)