Gold adatoms modulate sulfur adsorption on gold.

Sulfur adsorption on Au(111) at high coverage has been studied by density functional calculations. In this case S species organize into rectangular structures containing 8 S atoms irrespective of the S source, which have been alternatively assigned to adsorbed monomeric S, adsorbed S2, adsorbed monomeric plus S2 species, and gold sulfide. We found that monomeric S at the high coverage organizes into S2 species that are stabilized into the 8-S structures by Au adatoms, forming gold disulfide complexes (Au-(S2)4). The Au atoms could be provided by decomposition of more diluted AuS3 containing phases, as recently proposed, and direct removal from terraces and step edges, both explaining the surface coverage of vacancy islands coexisting with the 8-S structures. The gold-disulfide complexes capture the disorder shown in the experimental STM images, explain the intrigued features of XPS, and also, give a smooth pathway to gold sulfide formation at higher temperatures. More importantly, the gold-disulfide complexes allow a unified picture of the gold-sulfur surface chemistry at high coverage for thiols and adsorbed sulfur species where the surface chemistry remains under discussion.