Molecular orientation and ordered structure of benzenethiol adsorbed on gold(111)

The adsorption of benzenethiol on Au(lll) from aqueous solution has been investigated by using surface-enhanced infrared absorption spectroscopy (SEIRAS), scanning tunneling microscopy (STM), and cyclic voltammetry (CV). This molecule is dissociatively adsorbed on the surface as a Au benzenethiolate and forms a well-ordered monolayer with a commensurate (root 13x root 13)R13.9 degrees symmetry. The ordered phase is formed within a few minutes in 0.1 mM aqueous solution, and further immersion of the substrate results in the deposition of multilayers. The phenyl ring is tilted about 30 degrees from the surface normal in the monolayer. The coverage of this molecule is calculated to be 0.31 (or 0.71 nmol cm(-2)) from the (root 13 x root 13)R13.9 degrees symmetry, but it was estimated to be 0.23 (or 0.53 nmol cm(-2)) from the reductive desorption of the monolayer in alkaline solution. The discrepancy between the two measurements may be ascribed to the coadsorption of sulfur atoms and the presence of vacancies.