Photon Factory Activity Report 2019 #37 (2020)

BL-9C/2019G054

Development of A Facile Low-temperature Polarization-dependent Total Reflection
Fluorescence XAFS (LT-PTRF-XAFS)
1

Wang-Jae CHUN1,* and Hiroaki NITANI2
College of Liberal Arts, Division of Arts and Sciences, International Christian University,
3-10-2 Osawa, Mitaka, Tokyo, 181-8585, Japan
2
Institute of Materials Structure Science, Photon Factory,
1-1 Oho, Tsukuba, 305-0801, Japan

1 Introduction
Metal-support interaction is an important governing
factor of the catalytic activity in heterogeneous catalysts.
Unveiling the interaction, XAFS could be the mostpractical tool though it gives only one-dimensional
information in general. To overcome the limitation,
Polarization-dependent Total Reflection Fluorescence
XAFS (PTRF-XAFS) has provided three-dimensional
information that allows determining the metal-support
interfacial bonds.[1] However, this state-of-art technique isstill scope for improvement in S/N ratios.
In the previous proposal (2016G551), we have improved
the S/N ratios in higher frequency EXAFS oscillations by
the first low-temperature PTRF-XAFS (LT-PTRF-XAFS)
measurement system with a liquid He-flow cryostat[2].
However, there are issues in the cost of a liquid He and thesize of the system. In this report, we introduce our recent
progress in a simple LT-PTRF-XAFS system, which
achieves low cost while satisfying the improvement in S/Nratios.
2 Experiment
To maintain a total reflection condition at low
temperatures, we fabricated a compact liquid N2 dewar
which has no mechanical vibration while reducing thetemperature. The modified dewar (ca. 200 mL) has an Al
shroud with three Kapton window ports. The dewar wasinstalled to a high precision 3-axis stage (Fig. 1).
LT-PTRF-XAFS measurements were performed at theBL-9C/12C of PF (2.5 GeV, 450 mA, Si(111)). Cu K
Fluorescence signals were detected with 7-elements
Silicon Drift Detector (XSDD50-07, Techno AP, Japan).
The measurements were carried out in the parallel(s-pol)or perpendicular (p-pol) orientation relative to the electric
vector (E) of theincident X-rays.
The Cu-HKUST-1
thin film on a single
crystal TiO2(110)was prepared as asample. Details canbe found fromelsewhere.[3]Fig.1 A liquid N2
cooled LT-PTRFXAFS system.

3 Results and Discussion
Fig. 2 shows cooling performance. The modified dewar
requires only 15 min to 80 K and can keep the temperaturefor 2 hr with 200 mL N2(l).

Fig. 2 Performance of the LT-PTRF-XAFS system.
(a) required time to 80 K, (b) retention time at 80 K.
Fig. 3 shows the EXAFS spectra of Cu-HKUST1/TiO2(110) where E// [001] (s-pol) and E// [110] (p-pol)to the surface at 80 K. We obtained the reasonable
polarization-dependent EXAFS spectra at the 80 K,
successfully. We also found no specific difference insurface orientations. It suggests the thin film has weakorientation-dependence.

Fig. 3 the LT-PTRF-XAFS of Cu-HKUST-1/TiO2(110)(a) 𝑘 𝜒(𝑘) spectra, (b) FT results (𝑘 = 3~11Å ).
The further demonstration will explore various metal
nanoparticles highly dispersed on solid substrates.
Acknowledgment
This work was supported by JSPS KAKENHI (Grant
Number JP25410074).
References[1] W.-J. Chun et al., X-ray and Neutron Techniques for
Nanomaterials Characterization, Springer-Verlag
Berlin Heidelberg (2016).
[2] W.-J. Chun et al., Photon Factory Activity Report 2018
#36 (2019).
[3] M. Hashimoto et al., Electrochemistry. 82, 335, (2014).
*wchun@icu.ac.jp