The structure of the Au(111)/methylthiolate interface: New insights fromnear-edge x-ray absorption spectroscopy and x-ray standing waves

DOI: 10.1063/1.3102095

Authors: A. Chaudhuri (University of Warwick) , M. Odelius (Stockholm University) , R. Jones (University of Nottingham) , B. Detlefs (ESRF) , T.-l. Lee (Diamond Light Source) , D. P. Woodruff (University of Warwick)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Chemical Physics , VOL 130 (12) , PAGES 124708

State: Published (Approved)
Published: March 2009

Abstract: The local structure of the Au(111)(?3×?3)R30° -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 ? ? S–C resonance but also into a ? ? 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 ? ? S–Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the ? ? S–C resonance. The new NIXSW data show the S–C bond to be tilted by 61° 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.

Journal Keywords: Gold; X-Ray Absorption Near Edge Structure; Chemical Bonds; Adsorption; Surface Photoemission

Subject Areas: Chemistry, Physics, Biology and Bio-materials

Facility: ESRF

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