invited papers 168 # 2001 International Union of Crystallography  Printed in Great Britain ± all rights reserved J. Synchrotron Rad. (2001). 8, 168±172 Development of an in situ polarization- dependent total-re¯ection ¯uorescence XAFS measurement system Wang-Jae Chun, a ² Yasuhiro Tanizawa, a Takafumi Shido, a Yasuhiro Iwasawa, a Masaharu Nomura b and Kiyotaka Asakura c * a Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, b Photon Factory, Institute of Material Structure Science, Oho, Tsukuba 305-0801, Japan, and c Catalysis Research Center, Hokkaido University, Kita 11 Nishi 10, Kita-ku, Sapporo, 060-0811, Japan. E-mail: askr@cat.hokudai.ac.jp An in situ polarization-dependent total-re¯ection ¯uorescence X-ray absorption ®ne structure (PTRF-XAFS) spectroscopy system has been developed, which enables PTRF-XAFS experiments to be performed in three different orientations at various temperatures (273±600 K) and pressures (10 10 760 torr). The system consists of a measurement chamber and a preparation chamber. The measure- ment chamber has a high-precision six-axis goniometer and a multi- element solid-state detector. Using a transfer chamber, also operated under ultra-high-vacuum conditions, the sample can be transferred to the measurement chamber from the preparation chamber, which possesses low-energy electron diffraction, Auger electron spectro- scopy and X-ray photoelectron spectroscopy facilities, as well as a sputtering gun and an annealing system. The in situ PTRF-EXAFS for Cu species on TiO 2 (110) has been measured in three different orientations, revealing anisotropic growth of Cu under the in¯uence of the TiO 2 (110) surface. Keywords: polarization-dependent total-re¯ection ¯uorescence; metal±substrate interface; Cu/TiO 2 catalyst. 1. Introduction Most industrial catalysts are used in the form of supported-metal catalysts. The role of the support is not only to disperse the active sites but also to modify the catalytic properties through so-called `metal±support interactions'. Although a number of concepts have been proposed to explain the metal±support interaction, lack of accurate knowledge about the interface structures and the bonding features between active metal sites and support surfaces inhibits a full understanding of the essence of the metal±support interaction. Extended X-ray absorption ®ne structure (EXAFS) spectroscopy is one of the most powerful techniques currently used to study the structure of supported catalysts (Koningsberger & Prins, 1988; Iwasawa, 1996). In order to determine the interface structure in a supported catalyst, EXAFS has been applied to model catalysts in which small metal particles are deposited on powder oxides (van Zon et al., 1984; Martens et al. , 1988; Koningsberger & Gates, 1992; Asakura et al., 1985; Koningsberger et al., 1996). However, careful interpretation and analysis are required to elucidate the interface structures because the results derived from the usual EXAFS are averaged in all directions and the contribution from the interface structure is often weaker than that from the metal±metal interaction in the metal particles. EXAFS has a polarization dependence expressed as k 3 P cos 2  i   i k; 1 where (k),  i and  i (k) are an EXAFS oscillation, an angle between the ith bond and the polarization vector of the incident X-ray, and an EXAFS oscillation accompanying the ith bond, respectively. Hence, equation (1) indicates that if one can use a ¯at substrate with active metal species deposited thereon and set the sample surface parallel to the electric polarization vector, one can obtain the interface structure selectively. In order to investigate the structure of the metal species dispersed on the ¯at substrate, we have developed polarization-dependent total-re¯ection ¯uorescence X-ray absorption ®ne structure (PTRF- XAFS) spectroscopy (Asakura et al., 1993, 2000; Shirai & Iwasawa, 1996). The total-re¯ection ¯uorescence mode is necessary to obtain EXAFS of the surface species when the coverage of the surface species is less than one monolayer (Heald et al., 1984, 1988; Chen & Heald, 1993). We have applied the method to Co oxide on -Al 2 O 3 (0001), Cu oxide on -quartz (0001), Pt 4 clusters on -Al 2 O 3 (0001), and Mo oxide on rutile TiO 2 (110) (Shirai et al., 1992; Shirai, Asakura & Iwasawa, 1994; Shirai, Inoue et al. , 1994; Asakura et al., 1997; Chun Figure 1 The in situ polarization-dependent total-re¯ection ¯uorescence (PTRF) measurement chamber with the sample-transfer chamber. ² Present address: Center for Analytical Chemistry and Science, Inc., 8-3-1, Chu-o, Ami, Inashiki, Ibaraki 300-0332, Japan.