Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 24: Postersitzung (Epitaxie und Wachstum, Oxide und Isolatoren, Elektronische Struktur, Oberfl
ächenreaktionen, Adsorption an Oberfl
ächen, Organische Dünnschichten)
O 24.44: Poster
Mittwoch, 26. März 2003, 14:30–17:30, P1
Adsorption of thermal H on the basal plane and at step edges of graphite (0001) surfaces — •Thomas Zecho1, Andreas Güttler2, Clarissa Abetz2, and Jürgen Küppers1,2 — 1Max-Planck-Institut für Plasmaphysik (EURATOM Association), 95748 Garching, Germany — 2Experimentalphysik III, Universität Bayreuth, 95440 Bayreuth, Germany
Adsorption on the graphite basal plane is one of the simplest examples of reactions of H with graphitic surfaces. It is therefore of interest for a wide range of scientific areas. Based on the theoretical work done by the astrophysics community and our recent first experimental evidence, it is now established that H adsorbes on top of a C of the graphite basal plane by about 0.4 A causing an activation barrier of about 0.2 eV for the chemisorption of H. The present study has been performed in order to investigate the contribution from the step edges to the adsorption of H at graphite surfaces. Different graphites were used and characterised by scanning electron microscopy (SEM). Hydrogen atoms were generated by thermal dissociation of hydrogen molecules in a tungsten capillary heated to 2000 K and exposed to the graphites under UHV conditions at temperatures below 300 K. Subsequent heating of the samples leads to the desorption of H2 between 300 K and 600 K from the graphite basal plane and to a minor desorption of H2 and hydrocarbons between 700 K and 1300 K. The comparision between TD spectra from graphites of different qualities did allow the interpretation of the high temperature part as desorption from the step edges and did show the influence of the terrace size to the desorption from the basal plane.