Photon Factory Activity Report 2018 #36 (2019)

BL-9C/2016G551

Development of Low-temperature Polarization-dependent Total Reflection
Fluorescence XAFS (LT-PTRF-XAFS)
Wang-Jae CHUN(DEN)1,* and Hiroaki NITANI2
1
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

2 Experiment
To maintain a total reflection contion at low
temperatures, we modified a liquid He-flow cryostat(STVP-100, JANIS,U.S.A.) which has no
mechanical vibration
while reducing thetemperature.
The
modified cryostat wasinstalled to a highprecision 3-axis stage(Fig. 1). LT-PTRFXAFS measurements
were performed at theBL-9C of PF (2.5 GeV,450 mA, Si(111)).
Fig.1 LT-PTRF-XAFS system.
Fluorescence signals were detected with 7-elements
Silicon Drift Detector (XSDD50-07, Techno AP, Japan).
XAFS measurements were carried out in the parallelorientation relative to the electric vector (E) of theincident X-rays. The Cu-HKUST-1 thin film on a single
crystal Si(100) surface was prepared by a drop casting[2].
3 Results and Discussion
Fig. 2 (a) and (b) shows the
LT-PTRF-EXAFS
spectra of Cu-HKUST-1/Si(100) where E// [100] surface.
. It suggests that theWe found a fine shoulder in ~5
LT-PTRF-XAFS improves S/N ratios. Noteworthy is the
XANES feature (Fig. 2(c)). The weak pre-edge (appearedat around 8985 eV) at RT becomes a sharp feature at 4 K.
Moreover, we found that the feature was reversible. The
pre-edge feature has assigned to the 1s→ 4pxy dipolar
shakedown transition which indicates the existence ofCu(II). We, therefore, assumed that the reversible feature
would be related to the orientation of the ligands in CuHKUST-1.
(b)

3Fig. 2 Cu K-edge LTPTRF-XAFS of CuHKUST-1/Si(100)(a)
spectra, (b) FT,results
3~11(c) XANES spectra.

3|FT| of k χ(k) / Å-3-4(a)k χ(k) / Å

1 Introduction
Metal-support interaction is an essential 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 which allows determining the metal-support
interfacial bonds.[1] However, this state-of-art technique isstill scope for improvement in S/N ratios, S/B ratios, andtime resolution.
In the proposal (2016G551), we have challenged to
improve the S/N ratios in the PTRF-XAFS spectra byemploying a low-temperature measurement. Generally,temperature effects damp EXAFS amplitudes through thedynamic (thermal) disorders. Moreover, the effect relates
to the S/N ratios in higher frequency EXAFS oscillations.
A low-temperature measurement, therefore, has been
applied as an effective solution. However, the crucialdifficulty in isolating the mechanical vibration from acryostat disturbs to obtain LT-PTRF-XAFS spectra.
In the report, we intorduce our recent progress
suppressing the technical issue, and demonstrate the first
low-temperature PTRF-XAFS (LT-PTRF-XAFS) results.

(c)

Acknowledgment
This work was supported by JSPS KAKENHI GrantNumber JP25410074. We appreciate Prof. K. Asakura (ICAT, Hokkaido Univ.) for supporting the He-flow
cryostat and the XSDD dectecor.
References[1] W.-J. Chun et al., X-ray and Neutron Techniques for
Nanomaterials Characterization, Springer-Verlag
Berlin Heidelberg (2016).
[2] M. Hashimoto et al., Electrochemistry. 82, 335(2014).
*wchun@icu.ac.jp