The structure of the Au(111)/methylthiolate interface: new insights from near-edge x-ray absorption spectroscopy and x-ray standing waves.
2009 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 12, 124708- p.Article in journal (Refereed) Published
The local structure of the Au(111)(√3x√3)R30 degrees-methylthiolate surface phase has been investigated by S K-edge near-edge s-ray absorption fine structure (NEXAFS) both experimentally and theoretically and by experimental normal-incidence x-ray standing waves (NIXSW) at both the C and S atomic sites. NEXAFS shows not only excitation into the intramolecular σ*S-C resonance but also into a σ* S-Au orbital perpendicular to the surface, clearly identifying the local S headgroup site as atop a Au atom. Simulations show that it is not possible, however, to distinguish between the two possible adatom reconstruction models; a single thiolate species atop a hollow-site Au adatom or a dithiolate moiety comprising two thiolate species bonded to a bridge-bonded Au adatom. Within this dithiolate moiety a second σ* S-Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the σ* S-C resonance. The new NIXSW data show the S-C bond to be tilted by 61 degrees relative to the surface normal, with a preferred azimuthal orientation in <211>, corresponding to the intermolecular nearest-neighbor directions. This azimuthal orientation is consistent with the thiolate being atop a hollow-site Au adatom, but not consistent with the originally proposed Au-adatom-dithiolate moiety. However, internal conformational changes within this species could, perhaps, render this model also consistent with the experimental data.
Place, publisher, year, edition, pages
2009. Vol. 130, no 12, 124708- p.
Research subject Quantum Chemistry
IdentifiersURN: urn:nbn:se:su:diva-32125DOI: 10.1063/1.3102095ISI: 000264775200075PubMedID: 19334873OAI: oai:DiVA.org:su-32125DiVA: diva2:279502