AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS+OM-ThA

Paper SS+OM-ThA1
Non-dissociative Chemisorption of Methanethiol on Ag(110)- A Critical Result for Self-assembled Layer Formation

Thursday, November 6, 2003, 2:00 pm, Room 327

Session: Self-Assembled Monolayers
Presenter: J.-G. Lee, University of Pittsburgh
Authors: J.-G. Lee, University of Pittsburgh
J. Lee, University of Pittsburgh
J.T. Yates, Jr., University of Pittsburgh
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Three definitive experiments have been performed which show that CH@sub 3@SH does not dissociate upon chemisorption on clean Ag(110). On the clean Ag(110) surface, the adsorption in the first layer occurs at 0.5 ML, producing a (2x1) LEED structure. The undissociated molecule desorbs at ~140 K. Using a 50%-50% mixture of CH@sub 3@SD and CD@sub 3@SH, no evidence of S-H or S-D bond scission by isotope mixing between these molecules is found upon desorption. And finally, when the CH@sub 3@SH molecule is incident on clean Ag(110) surface in the temperature range from 240 K to 400 K, less than 1% of the incident molecules dissociate to produce adsorbed S. In contrast, when a sulfur-poisoned Ag(110) surface is exposed to CH@sub 3@SH, autocatalytic dissociation occurs below 240 K, producing CH@sub 4@, H@sub 2@S and adsorbed S atoms. These results are in striking contrast to the behavior of Cu(110) where CH@sub 3@SH dissociation occurs below 320 K leaving S. These results are of importance in understanding the self assembly of alkanethiol layers on silver where it has been commonly assumed that S-H bond scission occurs at room temperature. This work was supported by DOE-BES.