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The structure of the Au(111)/methylthiolate interface : new insights from near-edge X-ray absorption spectroscopy and X-ray standing waves

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Chaudhuri, Anindita, Odelius, Michael, Jones, R. G., Lee, Tien-Lin, Detlefs, B. and Woodruff, D. P.. (2009) The structure of the Au(111)/methylthiolate interface : new insights from near-edge X-ray absorption spectroscopy and X-ray standing waves. Journal of Chemical Physics, Vol.130 (No.12). p. 4708. ISSN 0021-9606

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Official URL: http://dx.doi.org/10.1063/1.3102095

Abstract

The local structure of the Au(111)([square root of]3×[square root of]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 sigma* S–C resonance but also into a sigma* 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 sigma* S–Au orbital that lies near parallel to the surface has a higher energy that overlaps that of the sigma* 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.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Adsorption -- Research, Binding sites (Biochemistry), Self-assembly (Chemistry) -- Research, Thin films, Multilayered, X-ray absorption near edge structure
Journal or Publication Title:	Journal of Chemical Physics
Publisher:	American Institute of Physics
ISSN:	0021-9606
Official Date:	26 March 2009
Volume:	Vol.130
Number:	No.12
Page Range:	p. 4708
Identification Number:	10.1063/1.3102095
Status:	Peer Reviewed
Access rights to Published version:	Open Access
Funder:	European Synchrotron Radiation Facility (ESRF)
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URI:	http://wrap.warwick.ac.uk/id/eprint/2697