|
The structural phases formed by atomic sulphur on Au(111) due to reaction with molecular S2 have been investigated by qualitative low energy electron diffraction (LEED), scanning tunnelling microscopy and normal incidence X-ray standing wavefield absorption (NIXSW) combined with X-ray photoelectron spectroscopy (XPS). Three phases are identified with increasing coverage, namely a newly-identified (5x5) phase, a (√3×√3)R30° phase, and a 'complex' phase. The (5x5) phase, with a LEED pattern having the appearance of a 'split-spot' (√3×√3)R30° pattern, is interpreted in terms of local (√3×√3)R30° ordering within a (5x5) ordered domain structure. The S atoms in the (5x5) phase occupy fcc hollow sites 1.56 Å above the outermost extended Au(111) bulk atomic scatterer plane. A specific model of the ordering in this phase is proposed that, together with the observed marginal stability of the true, long-range-ordered, (√3×√3)R30° phase, indicates significant short-range S-S repulsion and probably compressive surface stress. |