Hamburg 2001 – scientific programme
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O: Oberflächenphysik
O 33: Methodisches (Experiment und Theorie)
O 33.3: Talk
Thursday, March 29, 2001, 16:00–16:15, M
An enhanced probing depth in X-ray absorption spectroscopy — •Michael Zharnikov, Stefan Frey, Karin Heister, and Michael Grunze — Angewandte Physikalische Chemie, Universität Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg
In the partial electron yield (PEY) acquisition mode commonly used in X-ray absorption spectroscopy both elastically and inelastically scattered electrons contribute to the signal with the latter contribution presumably dominating. The related values of mean free path (MFP) should be, therefore, noticeably larger than the well-known inelastic mean free paths for electrons of definite kinetic energy. We have performed XPS and near edge X-ray absorption fine structure spectroscopy measurements for series of self-assembled monolayers of alkanethiols on gold substrate. The length of the alkyl chain and, subsequently, the film thickness was varied. In agreement with the expectations, the obtained effective MFPs for the Au 4f photoelectrons and CKLL Auger electrons in the PEY acquisition mode exceed the respective values for the elastically scattered electrons of the same kinetic energies (the Au 4f and CKLL electrons made up the elastic component of the acquired PEY signals). Furthermore, the PEY-MFP for the CKLL Auger electrons increased with decreasing retarding voltage of the PEY detector, which correlates with the increasing contribution of the inelastically scattered electrons in the acquired signal.