Photon Factory Activity Report 2014 #32 (2015) B

BL-9A/2014G552

Preparation of Dimeric Cu Species on a TiO2(110) Surface Premodified withMercaptobenzoic AcidSatoru Takakusagi*, Sirisit Natee, Yoshihiro Honda, Satoshi Seki, Horomitsu Uehara,
Tadashi Ohba, Hiroko Ariga, Kiyotaka Asakura
Hokkaido Univ., Sapporo 001-0021, Japansimulation (without polarization) using this model
structure is illustrated in Fig. 2(b) (red curve) together
with the experimental spectrum (E//[001], black curve),
indicating a fair agreement of the calculated spectrumwith the observed one. These results suggested that Cu
was nucleated at the S atom of the o-MBA molecule anddimeric Cu species was formed on a TiO2(110) surface.
We are now trying to determine a more detailed 3D
structure of the dimeric Cu species.
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10Fig. 1: (a)~(c) PTRF-EXAFS spectra of Cu/o-MBA/TiO2(110), respectively; (a) E// [001] , (b) [11̅0] , (c)[110]. (d) EXAFS spectrum of Cu foil.
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2 Experimental
Nb-doped (0.05 wt%) TiO2(110) surface was cleaned
by HF etching and annealing in air at 973 K for 1h. Thecleaned surface was immersed in 2 mM o-MBA ethanol
solution to modify the TiO2(110) surface with o-MBA
monolayer. Cu was vacuum-deposited on the o-MBAmodified surface, and the coverage was estimated to be
1.05 ML by XPS measurements (1 ML=5.2×1014/cm2).
PTRF-XAFS measurements were carried out at BL9A
with in-situ PTRF-XAFS chamber (base pressure 8 × 10-8Pa). XAFS analysis was carried out using REX2000 andFEFF8.40.

E//[110]

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1 Introduction
Precise size control of metal species on oxide surfaces,
especially in the range of <1 nm, is now highly important
to develop the next-generation catalysts, sensors, andelectronic devices. However this is not easy since metal
atoms are easily aggregated to form large particles onoxide surfaces. Our group has developed the“premodified surface method” to obtain a highly
dispersed metal species. An oxide surface is firstprecovered with an organic molecule possessing
functional groups which can strongly coordinate to ametal atom and fix to oxide surface [1-3].
Thenmetals are deposited. We have already succeeded in
preparing atomically dispersed Cu and Au species on theTiO2(110) surfaces premodified MBA (mercaptobenzoicacid, HS-C6H4-COOH) molecules, where mercapto group
acts as a coordinating site to the metal atoms andcarboxylic group as a binding part to the substrateTiO2(110) surface [2,3]. In this study, we attempted toprepare dimeric Cu species on a TiO2(110) surface
premodified with ortho-MBA (o-MBA), and the structureof the Cu species was examined by polarization
dependent total-reflection fluorescence (PTRF) EXAFS.

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3 Results and Discussion
Fig. 1(a)-(c) shows the observed Cu K-edge PTRFEXAFS spectra of the Cu/o-MBA/TiO2(110) in threedifferent polarization orientations. No significant
difference was found in the three polarization dependent
spectra. Preliminary curve fitting analysis of the observed
spectra revealed main contribution from Cu-Cu (2.58 Å)
and Cu-S (2.29Å) bonds.
FEFF simulation was performed to obtain information
on a more detailed structure of the Cu species. We tested
various structure models, and Fig. 2(a) shows one of thepossible model structures (triangle Cu2S).
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Fig. 2 (a) A possible model structure (brown ball: Cu,yellow ball: S). (b) FEFF simulation (E//[001]).
References[1] W.J. Chun et al., Chem. Phys. Lett. 433, 345 (2007).
[2] S. Takakusagi et al., Phys. Chem. Chem. Phys. 15,14080 (2013).
[3] K. Asakura et al., Faraday Discuss. 162, 165 (2013).
* takakusa@cat.hokudai.ac.jp

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