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O: Fachverband Oberflächenphysik
O 48: Surface dynamics I
O 48.4: Vortrag
Mittwoch, 24. März 2010, 11:15–11:30, H40
Neutral hydrogen desorption from graphite induced by ultra short laser pulses — •Robert Frigge1, Tim Hoger1, Björn Siemer1, Helmut Zacharias2, Thomas Olsen2, and Jakob Schiøtz1 — 1Physikalisches Institut, Universität Münster, Germany — 2CINF, Technical University of Denmark, Denmark
The desorption of hydrogen from HOPG is an important issue in the understanding of molecular hydrogen formation on durst particles upon irradiation. Surface mediated processes lead to H atom desorption. The velocity distribution of atomic hydrogen from HOPG is examined after surface excitation with fs pulses at λ =400 nm using a Ti:sapphire laser. Desorbing 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 desorbing hydrogen atoms.
Electron scattering calculations are performed employing a repulsive electronic state and the H-graphite adsorption potentials appropriate for different adsorption sites[1]. Besides populating different vibrationally excited states in multiple scattering events, velocity distributions for desorption out of different adsorption sites are obtained. A good agreement with the experimentally observed velocities is obtained, not only for the fast but also for the very slow atoms.
[1]L. Hornekær et al., Phy. Rev. Lett., 96, 156104 (2006)