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

Benzenethiol adsorption on Au(111) has been studied using synchrotron angle resolved ultraviolet photoelectron spectroscopy (ARUPS), high resolution e lectron energy loss spectroscopy (HREELS) and high resolution X-ray photoel ectron 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 line shapes and binding energies consistent with thiolate stoichiometry and chem ical shift expectations and UPS assignment of benzene-like molecular orbita ls. Based upon the intensity of the out-of-plane C-H deformation relative to th e in-plane C-H stretch, an adsorption geometry with the plane of the aromat ic ring largely parallel to the Au(111) surface is favoured. The polarisati on/angular dependence of the molecular orbital intensities in ARUPS confirm s 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 intensitie s indicates a flat-lying bonding arrangement with a tilt angle of the pheny l ring of 10+/-10 degrees with respect to the surface plane. The uptake of benzenethiol monitored by work function changes (Delta phi), low energy electron diffraction, and attenuation of the Au(111) Shockley su rface state suggests an adsorption mechanism involving the formation of two -dimensional islands without long range ordering to a 300 K saturation cove rage of 3.3 x 10(14) sulfur atoms cm(-2). (C) 1999 Elsevier Science B.V. Al l rights reserved.