AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM4
Adsorption and Abstraction of H Atoms on the Graphite (0001) Surface

Monday, November 4, 2002, 9:20 am, Room C-108

Session: Adsorption and Chirality
Presenter: T. Zecho, Max-Planck-Institut für Plasmaphysik (EURATOM Association), Germany
Authors: T. Zecho, Max-Planck-Institut für Plasmaphysik (EURATOM Association), Germany
A. Güttler, Universität Bayreuth, Germany
C. Drummer, Universität Bayreuth, Germany
X. Sha, University of Massachusetts
B. Jackson, University of Massachusetts
J. Küppers, Max-Planck-Institut für Plasmaphysik (EURATOM Association), Germany
Correspondent: Click to Email
The interactions of hydrogen atoms with graphite surfaces are of interest for many areas like astrophysics, plasma surface interactions in controlled fusion devices and diamond synthesises. Nevertheless most of the knowledge up to now is deduced from theoretical work and without experimental evidence. The present study has been performed in order to verify recent theoretical results on the interactions of hydrogen atoms with the graphite basal plane. Highly oriented pyrolytic graphite (HOPG-ZYH) was used and characterised by scanning electron microscopy (SEM) prior to the experiments. Hydrogen atoms were generated by thermal dissociation of hydrogen molecules in a tungsten capillary heated to 2000 K. Adsorption and abstraction were investigated by thermal desorption spectroscopy (TDS), electronic and vibrational energy loss spectroscopy (EELS, HREELS) and in situ measurment of the abstraction products. Admission of hydrogen atoms at low temperatures (100 K-300 K) leads to adsorption of hydrogen on graphite up to coverages of about 0.5 monolayer. In EEL spectra the intensity of the @pi@-plasmon of graphite decreases upon hydrogen adsorption indicating a decreasing sp@super 2@ character of surface carbon 2sp electrons. HREEL spectra allowed to determine the C-H normal and parallel vibrational frequencies which are close to theoretical predictions. Heating of H(D) covered graphite surfaces leads to desorption of hydrogen (deuterium) molecules with peaks between 300 K and 600 K. The thermal desorption peak maxima show a large isotope effect of about 50 K. The admission of deuterium atoms to H covered graphite surfaces leads to the release of HD and a very small amount of H@sub 2@. The abstraction reaction shows a coverage dependent cross section which decreases from about 16 Å@super 2@ at low coverages to about 4 Å@super 2@ close to saturation.