AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM6
Self Assembled Monolayers of Arenethiol Molecules on Cu(111)

Tuesday, November 16, 2004, 10:00 am, Room 210C

Session: Self Assembled Monolayers
Presenter: K. Wong, University of California, Riverside
Authors: K. Wong, University of California, Riverside
K.-Y. Kwon, University of California, Riverside
B.V. Rao, University of California, Riverside
A. Liu, University of California, Riverside
L. Bartels, University of California, Riverside
Correspondent: Click to Email
The utility of the thiol group on anchoring organic molecules to metal surfaces has been widely recognized. The thiol group makes sufficiently strong bonds with the metal substrate that stable monolayers are formed spontaneously even at room temperature in a solution environment. At low coverages and under ultra-high vacuum conditions isolated thiols exhibit significant surface mobility even at temperatures as low as 80K. We have studied monolayers of thiolphenol (TP) molecules and several halogen substituted para-X-TP derivates (where X is Br, Cl or F) at various coverages. All TPs adsorb with the benzene ring parallel to the surface and do not tilt to a vertical orientation as long as there is sufficient surface area available to accommodate all adsorbed molecules in a horizontal fashion. At such coverages we find a pronounced dependence of the ability of the TPs to form ordered films on the nature of their substitution. The most remarkable differences were found at incomplete coverage where the molecules have space to rearrange themselves into the optimal surface conformation and are not exposed to lateral stress. X-TP molecules form patterns of various degrees of complexity: Br-TP forms a simple (3x4) structure with one molecule per unit cell. Cl-TP films are made up of slightly more complicated unit cells involving two neighboring molecules whose sulfur atoms are located in different (hcp and fcc) Cu(111) hollow sites. F-TP molecule self assemble into a (8x8)R19@super o@ honeycomb pattern consisting of seven molecules per unit cell. Unsubstituted TP and pentafluoro-TP do not form any extended ordered patterns. This suggests that differences in the chemical properties between the para- and the meta-/ortho- substituents of TPs play a crucial role in the pattern formation process. We present a model based on quadrupolar intermolecular interaction to account for these observations.