Benzenethiol adsorption on Au(111) studied by synchrotron ARUPS, HREELS and XPS

Abstract

Benzenethiol adsorption on Au(111) has been studied using synchrotron angle resolved ultraviolet photoelectron spectroscopy (ARUPS), high resolution electron energy loss spectroscopy (HREELS) and high resolution X-ray photoelectron spectroscopy (XPS).At sub-monolayer and saturation coverages, the absence of an S–H stretching vibration indicates that the sulfhydryl hydrogen is lost during adsorption. The formation of a thiolate intermediate is supported by the presence of aromatic vibrations in HREELS spectra, carbon (1s) and sulfur (2p) XPS lineshapes and binding energies consistent with thiolate stoichiometry and chemical shift expectations and UPS assignment of benzene-like molecular orbitals.Based upon the intensity of the out-of-plane C–H deformation relative to the in-plane C–H stretch, an adsorption geometry with the plane of the aromatic ring largely parallel to the Au(111) surface is favoured. The polarisation/angular dependence of the molecular orbital intensities in ARUPS confirms that the phenyl ring is aligned largely parallel to the surface and that the orientation is not strongly coverage dependent. Polar angle dependence of the variation of the carbon (1s) to sulfur (2p) photoemission intensities indicates a flat-lying bonding arrangement with a tilt angle of the phenyl ring of 10±10° with respect to the surface plane.The uptake of benzenethiol monitored by work function changes (Δφ), low energy electron diffraction, and attenuation of the Au(111) Shockley surface state suggests an adsorption mechanism involving the formation of two-dimensional islands without long range ordering to a 300K saturation coverage of 3.3×1014 sulfur atomscm−2.