Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)
O 15.8: Poster
Freitag, 4. März 2005, 17:00–20:00, Poster TU D
Particle Size Effects in TPD: Adsorption of CO2 on Clean and Oxygen-Precovered Au(110)-(1x2) — •J.M. Gottfried1,2 and K. Christmann1 — 1Institut fuer Chemie der Freien Universitaet Berlin, Takustr. 3, D-14195 Berlin — 2Lehrstuhl fuer Physikalische Chemie II, Universitaet Erlangen-Nuernberg, Egerlandstr. 3, D-91058 Erlangen
Temperature programmed desorption (TPD) spectra of CO2 on Au(110)-(1x2) exhibit overlapping submonolayer and multilayer peaks, indicating that the intermolecular CO2-CO2 attraction is of similar strength as the CO2-gold interaction. Thus, layer-by-layer growth and three-dimensional growth are equally favoured. Accordingly, the TPD spectra show two anomalies: i) A low-temperature and a high-temperature state grow simultaneously, and ii) the second-layer TPD peak appears at a lower temperature than the multilayer peak. This behavior can be explained by three-dimensional growth of the Stranski-Krastanov type. For small CO2 aggregates, the surface energy contribution to the total energy increases the CO2 vapour pressure and, hence, the desorption rate (Kelvin effect), whereas larger crystallites inhibit the desorption by excluding a certain fraction of the total coverage from desorption. Semi-quantitative simulations of the TPD spectra, supplemented by UPS and work function measurements, support our growth and interaction model of the CO2 adsorbate on clean and oxidized gold.