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

Scanning tunnelling microscopy has been used to study the interaction of di methyl disulphide, (CH3S)(2), with Cu(111) at room temperature, which is kn own 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 obser ved. One of these, a hexagonal honeycomb phase, is proposed to involve brid ge and hollow site adsorption on an unreconstructed Cu surface and is metas table; it is identified as a methanethiolate species previously only studie d 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 i s unclear. (C) 2000 Elsevier Science B.V. All rights reserved.