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

The adsorption of benzenethiol on Au(lll) from aqueous solution has been in vestigated by using surface-enhanced infrared absorption spectroscopy (SEIR AS), 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)R 13.9 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 f rom the surface normal in the monolayer. The coverage of this molecule is c alculated 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)) f rom the reductive desorption of the monolayer in alkaline solution. The dis crepancy between the two measurements may be ascribed to the coadsorption o f sulfur atoms and the presence of vacancies.