Methanethiolate structural phases on Cu(1 0 0) and Cu(4 1 0)

Scanning tunnelling microscopy has been used to study the interaction of dimethyl disulphide and methanethiol with Cu(1 0 0) and Cu(4 1 0) surfaces at room temperature, conditions believed to lead to the formation of adsorbed methanethiolate CH3S–. On Cu(1 1 1) these interactions are known to produce a pseudo-(1 0 0) reconstruction of the surface, but with a periodicity some 14% larger than on the ideal Cu(1 0 0) surface. On Cu(1 0 0) there is no evidence of adsorbate-induced substrate reconstruction, with commensurate (2×2) and (defected) c(2×2) overlayers being formed, although at the highest coverages the surface appears to be characterised by a c(2×6) phase which is sometimes poorly ordered. On Cu(4 1 0) the structure formed on the (1 0 0) terraces appears to be c(2×2), although characteristic patterns of kink formation on the steps may be explained in terms of relief of adsorbate-induced compressive surface stress as may be expected if a larger lattice parameter is preferred. The c(2×6) phase on the extended (1 0 0) surface is explained in terms of a buckled c(2×2) structure, also a consequence of compressive surface stress relief.