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Your search keyword '"Uemura, Yohei"' showing total 4 results
Start Over Author "Uemura, Yohei" Publisher wiley-blackwell
4 results on '"Uemura, Yohei"'

1. Transient X‐Ray Absorption Near Edge Structure Spectroscopy Using Broadband Free‐Electron Laser Pulses.

Author

Juranić, Pavle, Cirelli, Claudio, Mamyrbayev, Talgat, Uemura, Yohei, Vila‐Comamala, Joan, Lima, Frederico Alves, Bacellar, Camila, Johnson, Philip J. M., Prat, Eduard, Reiche, Sven, Wach, Anna, Bykova, Iuliia, Kahraman, Abdullah, Kabanova, Victoria, Milne, Christopher, and David, Christian

Subjects
OXALATES, X-ray absorption near edge structure, ACQUISITION of data, SPECTROMETRY, BANDWIDTHS, FREE electron lasers, ABSORPTION, LASER pulses
Abstract

A new method for time‐resolved X‐ray absorption near edge structure (XANES) spectroscopy that enables faster data acquisition and requires smaller sample quantities for high‐quality data, thus allowing the analysis of more samples in a shorter time is introduced. The method uses large bandwidth free electron laser pulses to measure laser‐excited XANES spectra in transmission mode. A beam‐splitting grating configuration allows simultaneous measurements of the spectra of the incoming X‐ray Free Electron Laser (XFEL) pulses and transmission XANES, which is crucial for compensating the pulse‐dependent intensity and spectrum fluctuations due to the self‐amplified spontaneous emission operation. The implementation of this new methodology is applied on a liquid solution of ammonium iron(III) oxalate jet and is compared to previous results, showing great improvements in the speed of acquisition and spectral resolution, and the ability to measure a large 2‐D spectral‐time map quickly. [ABSTRACT FROM AUTHOR]

Published
2024
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2. Development of Surface Fluorescence X‐Ray Absorption Fine Structure Spectroscopy Using a Laue‐Type Monochromator

Author

Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Feiten, Felix E., Mukai, Shingo, 1000030359484, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, 1000060175164, Asakura, Kiyotaka, Wakisaka, Yuki, Kido, Daiki, Uehara, Hiromitsu, Yuan, Qiuyi, Feiten, Felix E., Mukai, Shingo, 1000030359484, Takakusagi, Satoru, Uemura, Yohei, Yokoyama, Toshihiko, Wada, Takahiro, Uo, Motohiro, Sekizawa, Oki, Uruga, Tomoya, Iwasawa, Yasuhiro, 1000060175164, and Asakura, Kiyotaka

Abstract

Surface fluorescence X-ray absorption fine structure (XAFS) spectroscopy using a Laue-type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X-rays from the bulk even in the presence of solution. We applied the technique to submonolayer (similar to 10(14) atoms cm(-2)) Pt on HOPG and successfully obtained high signal/noise in situ XAFS data in combination with back-illuminated fluorescence XAFS (BI-FXAFS) spectroscopy. This technique allows in situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes.

Published
2019

3. Dynamics of Photoelectrons and Structural Changes of Tungsten Trioxide Observed by Femtosecond Transient XAFS.

Author

Uemura, Yohei, Kido, Daiki, Wakisaka, Yuki, Uehara, Hiromitsu, Ohba, Tadashi, Niwa, Yasuhiro, Nozawa, Shunsuke, Sato, Tokushi, Ichiyanagi, Kohei, Fukaya, Ryo, Adachi, Shin‐ichi, Katayama, Tetsuo, Togashi, Tadashi, Owada, Sigeki, Ogawa, Kanade, Yabashi, Makina, Hatada, Keisuke, Takakusagi, Satoru, Yokoyama, Toshihiko, and Ohtani, Bunsho

Subjects
*PHOTOELECTRONS, *TUNGSTEN trioxide, *X-ray absorption, *ELECTRONIC structure, *FREE electron lasers, *FEMTOSECOND lasers, *PHOTOEXCITATION
Abstract

The dynamics of the local electronic and geometric structures of WO3 following photoexcitation were studied by femtosecond time-resolved X-ray absorption fine structure (XAFS) spectroscopy using an X-ray free electron laser (XFEL). We found that the electronic state was the first to change followed by the local structure, which was affected within 200 ps of photoexcitation. [ABSTRACT FROM AUTHOR]

Published
2016
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4. Co-Immobilization of a Palladium-Bisphosphine Complex and Strong Organic Base on a Silica Surface for Heterogeneous Synergistic Catalysis.

Author

Motokura, KEN, Saitoh, Koki, Noda, Hiroto, Uemura, Yohei, Chun, Wang ‐ Jae, Miyaji, Akimitsu, Yamaguchi, Sho, and Baba, Toshihide

Subjects
PALLADIUM compounds, NUCLEAR magnetic resonance spectroscopy, SURFACE chemistry, PHOSPHINE, CHEMICAL reactions
Abstract

Co-immobilization of a palladium-bisphosphine complex and a strong organic base, 1,4-diazabicyclo[2.2.2]octane (DABCO), on a silica support was successfully achieved. The new catalyst structure was characterized by X-ray photoelectron spectroscopy, solid-state NMR spectroscopy, X-ray absorption fine structure spectroscopy, and elemental analysis. Although the local structure of the Pd-bisphosphine complex was unaffected by the presence of DABCO on the same silica surface, its catalytic activity in allylation reactions of nucleophiles was significantly enhanced, achieving turnover numbers (TON) up to >10 000, owing to dual-activation of substrate molecules by the Pd complex and DABCO. [ABSTRACT FROM AUTHOR]

Published
2016
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