Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

9A/2005G203

Development of in-situ Angle Resolved Total Reflection Fluorescence XAFS(ARTRF-XAFS) Measurement Technique

Wang-Jae Chun1, 2, Naoki Watanabe3, Yuichiro Koike5, Kaoru Ijima4, Hidenori Ashima2, Gousuke
Tateno6, Masaharu Nomura5, Yasuhiro Iwasawa7, and Kiyotaka Asakura1
1Catalysis Research Center Hokkaido University, Sapporo 001-0021, Japan, 2CREST, JST, Saitama
332-0012, Japan, 3Department of Quantum Science and Engineering, Hokkaido University, Sapporo060-8628, Japan, 4Department of Electronic Engineering, Yamanashi University, Kofu 400-8510,Yamanashi, Japan, 5Photon Factory, Institute of Materials Structure Science, Tsukuba 305-0801,
Japan, , 6Kao Corporation, Material Development Research Laboratories, Wakayama 640-8580,
Japan, 7Department of Chemistry, Graduate School of Science, The University of Tokyo, Tokyo 1130081, Japan
Introduction
Gold has been regarded as an inert material forcatalytic applications before Haruta et al., have exhibitedthat the Au particles below 5 nm in size supported on TiO2
has unique catalytic properties in CO oxidation.[1]For understanding the further insight of Au-TiO2
interaction we attempt to determine the surface structureof Au clusters on TiO2(110) surface by the PTRF-XAFS
technique[2-6]. However, it is difficult to achieve thecomplete picture under the PTRF-XAFS measurement
using three orientations, i.e. x, y, and z directions because
the Au L3 edge absorption generally used in Au XAFS
measurement shows weak polarization dependencecompared to K edge absorption. To overcome the limit wedeveloped in-situ Angle Resolved Total Reflection
Fluorescence XAFS (ARTRF-XAFS) technique.
In this work we describe the ARTRF-XAFS techniqueand report the surface structure of Au clusters onTiO2(110) surface obtained by the new technique.

Fig. 1 shows the first ARTRF-XAFS spectra of 0.05
ML Au on the clean TiO2 (110) with Au foil as a reference.
Due to the anisotropic surface structure of TiO2(110)
surface the ARTRF-XAFS measurement was carried out
from E // [1-10] to E // [110] through E // [001]orientations.

Experimental
A TiO2(110) single crystal was cleaned by Ar ion
sputtering at room temperature, followed by annealing at1000 K. 0.05 ML Au was loaded to the cleaned surface byvacuum evaporation of Au wire. The Au coverages weremonitored by XPS. PTRF-XAFS was carried out with anin-situ PTRF-XAFS measurement chamber (a base-8
pressure of ca. 8 x 10 Pa) [6] and a Canberra 19-element
SSD in a fluorescence mode at BL9A. XAFS analysis
was performed with REX 2000 and FEFF 8. 0.

Figure 1 The ARTRF-XAFS spectra of Au / TiO2(110) surface. (a)XANES; (b) EXAFS.

Results and Discussion
To overcome the weak polarization dependence in Au
L3 edge absorption we attempt to increase the number ofXAFS measurement at the various angles between asample surface and the electric vector (E) of X-ray.
Another important point in the ARTRF-XAFS technique
is to keep a total reflection condition constantly for
obtaining a high signal to background ratio. We havecleared the technical difficulty by optimizing the threeaxes (θ, ψ, φ) in a UHV-compatible 6-axis goniometer.[6]74Users' Report

First, there was no difference in all ARTRF-XANES
spectra which showed small 1s→5d transition indicatingthe presence of metallic Au. In EXAFS region thepolarization dependent spectra showed a little difference
from each other and the period of the oscillations werecomparable to that of Au foil. Considering thesepreliminary ARTRF-XAFS results we assumed that 3
dimensional small Au particles may be formed on theclean TiO2(110) surface but the detail analysis on themorphology is in progress.
References[1] M. Haruta et al., Catal. Survyes Jpn. 1 (1997) 61.
[2] W.-J. Chun et al., J. Phys. Chem. B 102 (1998) 9006.
[3] Y. Tanizawa et al., J. Phys. Chem. B 107 (2003) 12917.
[4] K. Ijima et al., Chem. Phys. Lett. 384 (2004) 134.
[5] Y. Koike et al., Chem. Phys. Lett. 421 (2006) 27.
[6] W.-J. Chun et al., J. Synchrotron Rad., 8(2001) 168.
*wchun@cat.hokudai.ac.jp