Electronic structure of methanethiolate self-assembled on the Cu(1 0 0) surface

We present a high-resolution UV photoelectron spectroscopy investigation of methanethiolate (CH3S–) adsorbed on the clean Cu(1 0 0) surface, by vapour-phase deposition of dimethyl disulphide [(CH3S)2, DMDS] in controlled ultra-high-vacuum conditions (UHV). The low-energy electron-diffraction (LEED) pattern reveals the formation of a first p(2 × 2) low-density phase up to 2.7 Langmuir (L) exposure, followed by a two-domain c(2 × 6) high-density phase, at room temperature. We identify the valence band peaks specific of the corresponding structural phases due to S–Cu bond formation, and in particular a different spectral density of electronic states for the two long-range ordered phases is brought to light. Keeping the substrate at low-temperature, a physisorbed multilayer phase of un-dissociated DMDS molecules grows-up on top of the first chemisorbed monolayer, with a clear long-range ordered c(2 × 2) structure.