Role of Gold Adatoms in the Adsorption of Sulfide Species on the Gold(001)-hex Surface

We have studied the adsorption of reduced sulfur species on the Au(001)-hex surface from diluted ethanolic sulfide solutions by STM, XPS, electrochemical techniques, and DFT calculations. Our results reveal the absence of S multilayers because all S species are bonded to Au surface atoms. Monomeric S adsorbs at hollow sites forming a (2 × 2) lattice, while S2 species either capture the gold adatoms (Auad) that result from the hex lifting or remove Auad from the substrate forming well-ordered S8-like structures. These are formed by four S2 species coordinated by a central Auad, with AuSS interatomic distances closely resembling those of a metal disulfide. Our results explain not only the predominant surface structures on the gold surface but also topographic features, like Auad islands and Au vacancy islands, and also the chemical nature of adsorbed species from XPS S 2p spectra. In contrast to the S heads of small aromatic thiols, which exhibit a low affinity for Auad, strongly reactive sulfide species re...