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The structure of the Au(111)/methylthiolate interface: New insights fromnear-edge x-ray absorption spectroscopy and x-ray standing waves
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
Added On:
19/08/2009 23:07
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