AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP3
Geometric and Electronic Structure of Self-Assembled Monolayers on Noble Metal Surfaces: Dodecanethiol on Au, Ag, and Pt

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: H. Geisler, Xavier University
Authors: T.M. Sweeney, University of New Orleans
J.M. Burst, University of New Orleans
P.S. Robbert, University of New Orleans
J.W. Hobson, University of New Orleans
S.M. Huston, University of New Orleans
C.A. Ventrice, Jr., University of New Orleans
B. Hayes, Xavier University
H. Geisler, Xavier University
Correspondent: Click to Email
Self-assembled monolayers (SAMs) have been grown by vapor deposition in UHV and by solution growth in ambient conditions on Au(111), Ag(111), Pt(111), and Pt(100) surfaces. The geometric structure of the SAMs has been studied with low energy electron diffraction (LEED), and the electronic structure has been measured with synchrotron-based ultra-violet photoelectron spectroscopy (UPS). The LEED results for Au provide evidence for a lying down, striped phase from 2 L to 40 kL, a disordered, mixed phase up to ~2 ML, and a standing-up, @sr@3x@sr@3 R30° phase beyond ~2 ML of thiol dose. Vapor deposition on Ag results in a disordering of the surface, with a complete loss of the LEED pattern by ~5 kL. Ordered overlayer structures are observed on both the Pt(111) and Pt(100) surfaces at thiol doses below 1 L. For instance, a p(2x2) LEED pattern is observed at 0.1 L which transforms to a @sr@3x@sr@3 R30° pattern at ~.25 L on the Pt(111) surface. Doses beyond ~2 L result in a disordered overlayer on this surface. The UPS spectra for solution growth SAMs on all three substrates are very similar. Four distinct peaks at 6.5, 10, 14, and 20 eV whose intensities are independent of the substrate are observed. The electronic structure of the vapor deposited films depends very strongly on the substrate. Weak thiol peaks are observed for coverages up to 100 kL on Au(111), consistent with the slow uptake observed with LEED. Emission features consistent with a fully saturated SAM are observed on Ag(111) for a dose of ~8 kL. Very weak thiol peaks are observed on the Pt surfaces for coverages up to 100 kL, which indicates that the uptake on Pt is slower than on Au. The ordered overlayer LEED patterns at low coverages, coupled with the very weak thiol features in UPS, point to a dissociative adsorption geometry for vapor deposition on Pt.