title: Coverage effects and the nature of the metal-sulfur bond in S/Au(111): high-resolution photoemission and density-functional studies.
abstract: The bonding of sulfur to surfaces of gold is an important subject in several areas of chemistry, physics, and materials science. Synchrotron-based high-resolution photoemission and first-principles density-functional (DF) slab calculations were used to study the interaction of sulfur with a well-defined Au(111) surface and polycrystalline gold. Our experimental and theoretical results show a complex behavior for the sulfur/Au(111) interface as a function of coverage and temperature. At small sulfur coverages, the adsorption of S on fcc hollow sites of the gold substrate is energetically more favorable than adsorption on bridge or a-top sites. Under these conditions, S behaves as a weak electron acceptor but substantially reduces the density-of-states that gold exhibits near the Fermi edge. As the sulfur coverage increases, there is a weakening of the Au-S bonds (with a simultaneous reduction in the Au --> S charge transfer and a modification in the S sp hybridization) that facilitates changes in adsorption site and eventually leads to S-S bonding. At sulfur coverages above 0.4 ML, S(2) and not atomic S is the more stable species on the gold surface. Formation of S(n)(n > 2) species occurs at sulfur coverages higher than a monolayer. Very similar trends were observed for the adsorption of sulfur on polycrystalline surfaces of gold. The S atoms bonded to Au(111) display a unique mobility/reactivity not seen on surfaces of early or late transition metals.
authors.affiliation: Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11953, USA.
authors.forename: José A
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Joseph
authors.initials: J
authors.lastname: Dvorak
authors.forename: Tomas
authors.initials: T
authors.lastname: Jirsak
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.forename: Jan
authors.initials: J
authors.lastname: Hrbek
authors.forename: Yosslen
authors.initials: Y
authors.lastname: Aray
authors.forename: Carlos
authors.initials: C
authors.lastname: González