IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS+BI-TuM

Paper SS+BI-TuM6
Structure of Alkyl Thiol and Dialkyl Disulfide on Au(111)

Tuesday, October 30, 2001, 10:00 am, Room 120

Session: Poirier Memorial Session: Self-Assembled Monolayers I
Presenter: H. Nozoye, Nanotechnology Research Institute, AIST, Japan
Authors: H. Nozoye, Nanotechnology Research Institute, AIST, Japan
T Hayashi, University of Tsukuba, Japan
C. Kodama, University of Tsukuba, Japan
Y. Morikawa, JRCAT, AIST, Japan
Correspondent: Click to Email
The structure and formation process of self-assembled monolayers on Au(111) have been a long-standing unsolved problem. We determined the adsorption state of alkane thiol and dialkyl disulfide with different alkyl chain length on Au(111), which are prototypical self-assembled monolayer systems, by using temperature programmed desorption (TPD), high sensitivity low energy electron diffraction (LEED), high resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculation. We concluded that the SH bond of alkane thiol and the SS bond of dialkyl disulfide break below room temperature, spontaneously desorbing hydrogen and resulting in the formation of highly ordered adsorption state of thiolate on the surface. The spectra above 500cm@super-1@ contain the information of the orientation of the alkyl moiety, however, those of low energy region contain the information of the bonding between S and Au. HREELS spectra of low energy region were almost the same for all the thiolate species, irrespective of the difference of the coverage of the thiolate and of the chain length of alkyl moiety, although the spectra above 500cm@super-1@ were changed depending on the coverage of the thiolate species. The change of the HREELS spectra above 500cm@super-1@ agreed with the conclusion obtained from STM measurements, that is the lying-down configuration in the low coverage region and standing-up configuration at the saturation coverage. The HREELS spectra of the low energy region were analyzed with the DFT calculation; The location of S of the thiolate on Au(111) is the bridge site and the SC bond is inclined about 50 degree from the surface normal. From these results we concluded that the structure of the root part of the thiolate species is common, at least for alkyl thiolate with relatively short chain, notwithstanding the difference of the orientation of the alkyl moiety, that is the lying-down and standing-up structures.