Research Theme

Exploitation of Novel Spectroscopic Methods for Material and Surface Science

Keywords

X-Ray Absorption Spectroscopy, Surface & Thin Film Magnetism, Ambient Pressure Hard X-Ray Photoelectron Spectroscopy

For the developments of novel functional materials, it is quite important to exploit simultaneously new analytical methods based on advanced technology. Novel materials and devices often require spatial and/or time resolved analysis to optimize their qualities. In our group, we have been exploiting spectroscopic methods for material and surface science using mainly synchrotron radiation (SR) and partly lasers.

The present first subject is the exploitation of ambient pressure hard x-ray photoelectron spectroscopy (HAXPES) and its application to polymer electrolyte fuel cells (PEFC) under working conditions. In 2017, we succeeded in the HAXPES measurement under real ambient pressure of 10⁵ Pa for the first time in the world. We are investigating working PEFC by the technique for the elucidation of degradation and/or poisoning mechanisms of PEFC to improve its performance with longer life time.

The second subject is the ultrafast (<100 fs) time resolved soft x-ray absorption measurements of spin dynamics in magnetic thin films in order to understand element-specific magnetization reversal mechanisms.

Ambient pressure hard x-ray photoelectron spectroscopic system.

(a) Apparatus installed at SPring-8 Beamline 36XU. (b) Au 4f HAXPES of Au(111) at a real ambient pressure of 10⁵ Pa. (c) S 1s HAXPES of the anode Pt and Pt₃Co electrodes of aged (fresh) and degraded polymer electrolyte fuels cells under working conditions. The Pt₃Co electrode is found to be more tolerant against S than the Pt electrode. (d) Quick HAXPES measurements of the cathode Pt of the polymer electrolyte fuels cells upon abrupt change of the cathode-anode voltage from 0.4 to 1.2 V. The time resolution is 500 ms.

Selected Publications

1. “Quick Operando Ambient Pressure Hard X-ray Photoelectron Spectroscopy for Reaction Kinetic Measurements of Polymer Electrolyte Fuel Cells” T. Nakamura, Y. Takagi, S. Chaveanghong, T. Uruga, M. Tada, Y. Iwasawa And T. Yokoyama, J. Phys. Chem. C 124, 17520 (2020).
2. “X-ray photoelectron spectroscopy under real ambient pressure conditions” Y. Takagi, T. Nakamura, L. Yu, S. Chaveanghong, O. Sekizawa, T. Sakata, T. Uruga, M. Tada, Y. Iwasawa and T. Yokoyama, Appl. Phys. Exp. 10, 076603 (2017).
3. “Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS” Y. Uemura, D. Kido, Y. Wakisaka, H. Uehara, T. Ohba, Y. Niwa, S. Nozawa, T. Sato, K. Ichiyanagi, R. Fukaya, S. Adachi, T. Katayama, T. Togashi, S. Owada, K. Ogawa, M. Yabashi, K. Hatada, S. Takakusagi, T. Yokoyama, B. Ohtani, and K. Asakura, Angew. Chem. Int. Ed. 55, 1364 (2016).
4. “Anharmonicity and Quantum Effects in Thermal Expansion of an Invar Alloy” T. Yokoyama and K. Eguchi, Phys. Rev. Lett. 107, 065901 (2011).
5. “Magnetic circular dichroism near the Fermi level” T. Nakagawa and T. Yokoyama, Phys. Rev. Lett. 96, 237402 (2006).