The evolution of benzenethiol self-assembled monolayer on the Cu(1 0 0) surface

Benzenethiol (C6H5SH) adsorption on the Cu(1 0 0) surface at room temperature has been studied using high resolution UV photoelectron spectroscopy (HRUPS), low energy electron diffraction (LEED) and work function change (ΔΦ). Benzenethiol reacts with the copper surface, forming an S–Cu bond and an ordered thiolate layer. Two subsequent phases of the self-assembled monolayer formation have been clearly identified as a function of exposure. At low coverage, a c (4 × 4) reconstruction is observed in the LEED pattern, and the valence photoemission signals are consistent with flat molecular arrangement on the Cu(1 0 0) surface, where the phenyl group interacts via the π orbitals. At higher coverage, the LEED pattern shows a high density phase with c (2 × 6)-symmetry; in the photoemission spectra the signals coming from the molecular orbitals localized on the benzene ring closely resemble the features observed in the gas phase spectra, thus suggesting an upright position of the molecule.