Berlin 2015 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe
O: Fachverband Oberflächenphysik
O 71: Surface Dynamics
O 71.1: Poster
Mittwoch, 18. März 2015, 18:15–21:00, Poster A
Femtosecond Laser-induced Desorption of Atomic and Molecular Hydrogen Isotopes from Graphite — •Robert Frigge, John D. Thrower, and Helmut Zacharias — Physikalisches Institut, Universität Münster, Germany
In the interstellar cycle of matter the formation of molecular hydrogen by recombination of adsorbed atoms on dust particles is an important process. In photon dominated regions this process is likely to be induced by radiation. Here, we examine the desorption of H and H2 from HOPG following surface excitation with fs-laser pulses at λ = 400 nm. Desorbed neutral species are analyzed by state-selective ionization and a time-of-flight detector. The desorbing H atoms show three different kinetic energy distributions, while for H2 only a very low energy distribution with <Ekin> = 60 meV is found. Electron scattering calculations [1] have been performed, taking into account different H-graphite adsorption potentials appropriate for different adsorption sites(para-, ortho- configuration) [2]. A nonlinear fluence dependence of the atomic desorption yield allows two-pulse correlation measurements. For the para-sites a FWHM of 600 fs can be explained by coupling the desorption to electrons, while the ortho-sites yield a distribution with a dip at 1 ps which cannot be explained by this model. We consider the possibility that the excitation of optical phonons, which occurs within 1 ps [3], is responsible for this dip.
[1]R. Frigge et al., Phys. Rev. Lett., 104, 256102 (2010)
[2]L. Hornekær et al., Phys. Rev. Lett., 97, 186102 (2006)
[3]M. Breusing et al., Phys. Rev. Lett., 102, 086809 (2009)