AVS 47th International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF-WeA

Paper OF-WeA8
X-Ray Induced Changes in Thiol-SAMs on Gold

Wednesday, October 4, 2000, 4:20 pm, Room 313

Session: Self-Assembled Monolayers: Electron Transfer and Film Properties
Presenter: A. Terfort, University of Hamburg, Germany
Authors: B. Zeysing, University of Hamburg, Germany
T. Eickhoff, University of Hamburg, Germany
W. Drube, Hamburger Synchrotronstrahlungslabor HASYLAB at Deutsches Elektronensynchrotron DESY, Germany
A. Terfort, University of Hamburg, Germany
Correspondent: Click to Email
Self-assembled monolayers (SAMs), in particular SAMs of alkanethiols on coinage metals, such as gold, receive a growing interest as convenient possibility to modify surfaces in an experimentally simple but very well adjustable manner. Since these layers are very thin (about 0.5 to 10 nm), they are typically characterized by surface sensitive techniques, often involving x-rays. On the other hand, it is known for some time that these monolayers are subject to massive changes upon irradiation, mainly caused by primary or secondary electrons generated in the supporting high-z material, which penetrate the monolayer.@footnote 1-4@ These electrons remove binding electrons from the molecules by impact ionization, leaving positive charges (holes) within the surface molecules. In alkane chains these holes remain localized and trigger chemical reactions. This results in altered monolayers with different properties and'mixed' results which are usually difficult to interpret. In our talk, we present results obtained by using synchrotron radiation based methods to demonstrate how fast monolayers transform under illumination with x-rays, and what the detailed mechanism of this transformation is. Using total external reflection x-ray photoelectron spectroscopy (TER-XPS),@footnote 5@ we could determine the fate of the sulfur atoms. By understanding the mechanisms of destruction, we were able to design SAMs with significantly increased stability towards x-rays. @FootnoteText@ @footnote 1@Wirde, M.; Gelius, U.; Dunbar, T.; Allara, D. L. Nuclear Instr. Methods Phys. Res. B 1997, 131, 245. @footnote 2@Zubragel, Ch.; Deuper, C.; Schneider, F.; M. Neumann, N.; Grunze, M.; Schertel, A.; W@um o@ll, Ch. Chem. Phys. Lett. 1995, 238, 308. @footnote 3@Olsen, C.; Rowntree, P. A. J. Chem. Phys. 1998, 108, 3750. @footnote 4@Zerulla, D.; Chass@aa e@, T. Langmuir 1999, 15, 5285. @footnote 5@M.J. Bedzyk, G.M. Bommarito, J.S. Schildkraut, Phys. Rev. Lett. 1989, 62, 1376.