Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 26: Adsorption an Oberflächen II

O 26.5: Vortrag

Dienstag, 9. März 2004, 16:45–17:00, H45

Photodesorption of small molecules adsorbed on ultrathin Ag — •Olaf Weisse, Claudia Wesenberg, and Eckart Hasselbrink — FB Chemie, Universitaet Duisburg-Essen, Universitaetstr. 5, 45117 Essen, Germany

Since the early 1990, Ag is known to grow on the Si(100) surface in a layer-by-layer fashion. The resulting surface forms an epitaxial Ag(111) layer. These ultrathin Ag films(20-100ML) are ideally suited to study the elektron dynamics in such films and the influence of the film thickness on charge transfer to the adsorbate and subsequent photodesorption. In our experiments, NO₂ is chosen as the probe molecule. Its adsorbtion is performed at 95 K on the Ag-covered Si(100) surface. Photodesorption is induced using a Nd:YAG laser (2.3eV/3.5eV/4.6eV) and the desorbed molecules are detected by QMS. The film thickness is varied in order to obtain information about the charge transfer dynamics between the ultrathin Ag film and the NO₂ adsorbate. The photodesorption cross-section of NO₂ is expected to decrease with increasing film thickness. We belive that the photodesorption cross-section will increase due to hot electrons generated in the semiconductor.