AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThP

Paper AS-ThP4
XPS and ISS Study of X-ray Damage of Alkanethiol Self-Assembled Monolayers on Gold and Silver

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Aspects of Applied Surface Science Poster Session
Presenter: D.E. King, National Renewable Energy Laboratory
Authors: D.E. King, National Renewable Energy Laboratory
L.S. Dake, National Renewable Energy Laboratory
A.W. Czanderna, National Renewable Energy Laboratory
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X-ray photoelectron spectroscopy (XPS) has been extensively used to study the chemistry of self-assembled monolayers (SAMs). While XPS is often considered the most non-destructive surface analysis technique, it is known that X-ray exposure and the resulting secondary electron emission can alter the reactivity of many materials. Organic materials can be particularly susceptible to damage resulting from X-ray bombardment during XPS. We have studied the effects of both Mg and Al K-alpha X-ray exposure on acid and methyl functionalized alkanethiol SAMs on gold and silver substrates. In the methyl terminated SAMs, a 20 percent reduction in C 1s peak area results after a 3 hour X-ray exposure. In the acid-terminated SAMs, both carbon and oxygen XPS signals decrease rapidly, with a relatively greater loss in the oxygen signal. Ion scattering spectroscopy (ISS) depth profiles indicate that it takes longer to sputter the irradiated SAMs than non-irradiated SAMs. We conclude that chemical changes in the monolayers result from the X-ray exposure. Although these changes are not detectable with XPS, the increased resistance to sputtering by the ISS beam indicates changes in bonding that are consistent with C-C crosslinking between the chains in the SAMs. XPS and ISS data will be presented for methyl and acid terminated alkanethiols after subjecting the SAMs to increasing times of X-ray exposure. This work was performed under DOE contract DE-AC36-83CH10093 @FootnoteText@ After Aug. 1, address for Dr. L. S. Dake is Susquehanna University, Selinsgrove, PA 17870-1001