Electronic structure of methanethiolate self-assembled on the Cu(100) surface

We present a high-resolution UV photoelectron spectroscopy investigation of methanethiolate (CH3S-) adsorbed on the clean Cu(100) surface;'by vapour-phase deposition of dimethyl disulphide [(CH3S)(2), DMDS] in controlled ultrahigh-vacuum conditions (UHV). The low-energy electron-diffraction (LEED) pattern reveals the formation of a first p(2 x 2) low-density phase, up to 2.7 Langmuir (L) exposure, followed by a two-domain c(2 x 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 x 2) structure. (C) 2004 Elsevier B.V. All rights reserved.