Scanning tunnelling microscopy study of the interaction of dimethyl disulphide with Cu(111)

Scanning tunnelling microscopy has been used to study the interaction of dimethyl disulphide, (CH3S)2, with Cu(111) at room temperature, which is known to produce adsorbed methanethiolate, CH3S-, by SS bond scission at the surface. The results provide clear evidence for the formation of a pseudo-square surface reconstruction induced by the adsorbate; this reconstruction can be reconciled with the results of previous structural studies of this surface by the techniques of X-ray standing wave and surface extended X-ray absorption fine structure. Two further ordered adsorption phases are observed. One of these, a hexagonal honeycomb phase, is proposed to involve bridge and hollow site adsorption on an unreconstructed Cu surface and is metastable; it is identified as a methanethiolate species previously only studied at low temperature by photoelectron spectroscopy and X-ray standing waves. A third phase of hexagonal symmetry appears to be an alternative endpoint to the pseudo-square phase, but may be due to higher adsorbate coverages; the nature of the structure of the underlying copper surface in this case is unclear.