High-resolution XPS study of decanethiol on Au(111): Single sulfur-gold bonding interaction

The chemisorption of 1-decanethiol on the Au(111) single crystal has been studied with synchrotron-based, high-resolution photoemission spectroscopy with molecular film prepared from both gas-phase dosing and solution immersion to vary surface coverage over a wider range. The structure of the molecular film, determined separately via low-energy electron diffraction, includes a c(23 x root3) stripe phase and c(3 x 2root3) saturated phases. Careful curve fitting of the S 2p(2/3) core level reveals that there is only one sulfur species at a binding energy of 162.1 eV in the film and the spectrum of the S 2p(2/3) core level does not vary with the surface coverage and existence temperature of the decanethiolate. This finding is inconsistent with the sulfur-pairing model proposed based on X-ray scattering and standing wave studies. Up to two C 1s core levels at 284.0 and 285.0 eV can be observed, depending on the surface coverage. Angle-resolved X-ray photoelectron spectroscopy measurements are utilized to provide a direct correlation between C Is binding energy and film thickness. It is argued that the difference in C 1s binding energy is not due to chemical shift but results from the screening difference of substrate electrons, that depends on the orientation of the decanethiolate film.