Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 31: Organische Dünnschichten II
O 31.2: Vortrag
Donnerstag, 27. März 2003, 15:15–15:30, HSZ/02
The limits of the dipole approximation in NIXSW: NTCDA on Ag(111) — •J. Stanzel1, L. Kilian1, W. Weigand1, H. Meyerheim2, M. Sokolowski3, C. Kumpf1, and E. Umbach1 — 1Experimentelle Physik 2, Univ. Würzburg — 2MPI für Mikrostrukturphysik, Halle — 3Inst. f. Physikalische und Theoretische Chemie, Univ. Bonn
The properties of organic thin films are often dominated by interface effects. Thus a deeper understanding of the interaction of the organic molecules with inorganic substrates is a key issue. A powerful tool for obtaining detailed structural information – e.g., exact atomic coordinates which enable quantum chemical calculations – is the (normal incidence) x-ray standing wave (NIXSW) technique. However, for an analysis of organic molecules, which contain low-Z atoms only, this is a difficult issue since the x-ray fluorescence signal is too weak and the dipole-approximation is no longer sufficient to describe the photoemission process. Recently, the effect of non-dipolar contributions became subject of theoretical and experimental investigations, and the Auger signal was employed to avoid this problem. We report on a comparison of O1s photoelectron and O KLL Auger data obtained in a NIXSW experiment on a coherent monolayer of NTCDA on Ag(111). It is demonstrated, that only after a correction of the measured Auger yield for contributions stimulated by photoelectrons from the Ag substrate, a good agreement of O1s and O KLL results can be obtained using reasonable corrections for the non-dipolar contributions to the photoelectron yield. The distance between the molecular plane and the topmost substrate layer is 3.08(3)Å, and hence considerably smaller than a Van der Waals distance.