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K
(Zn
Mn
)
As studied by X-ray magnetic circular dichroism and resonant inelastic X-ray scatteringSuzuki, Hakuto*; Zhao, G.*; Okamoto, Jun*; Sakamoto, Shoya*; Chen, Z.-Y.*; Nonaka, Yosuke*; Shibata, Goro; Zhao, K.*; Chen, B.*; Wu, W.-B.*; et al.
Journal of the Physical Society of Japan, 91(6), p.064710_1 - 064710_5, 2022/06
Times Cited Count：0 Percentile：0(Physics, Multidisciplinary)Kobayashi, Masaki*; Anh, L. D.*; Suzuki, Masahiro*; Kaneta-Takada, Shingo*; Takeda, Yukiharu; Fujimori, Shinichi; Shibata, Goro*; Tanaka, Arata*; Tanaka, Masaaki*; Oya, Shinobu*; et al.
Physical Review Applied (Internet), 15(6), p.064019_1 - 064019_10, 2021/06
Times Cited Count：4 Percentile：27.71(Physics, Applied)Mn
As via soft X-ray magnetic circular dichroismTakeda, Yukiharu; Oya, Shinobu*; Pham, N. H.*; Kobayashi, Masaki*; Saito, Yuji; Yamagami, Hiroshi; Tanaka, Masaaki*; Fujimori, Atsushi*
Journal of Applied Physics, 128(21), p.213902_1 - 213902_11, 2020/12
Times Cited Count：8 Percentile：44.34(Physics, Applied)
impurity band state as the origin of high Curie temperature in the 
-type ferromagnetic semiconductor (Ga,Fe)SbTakeda, Takahito*; Sakamoto, Shoya*; Araki, Kosei*; Fujisawa, Yuita*; Anh, L. D.*; Tu, N. T.*; Takeda, Yukiharu; Fujimori, Shinichi; Fujimori, Atsushi*; Tanaka, Masaaki*; et al.
Physical Review B, 102(24), p.245203_1 - 245203_8, 2020/12
Times Cited Count：7 Percentile：44.34(Materials Science, Multidisciplinary)Hirahara, Toru*; Otrokov, M. M.*; Sasaki, Taisuke*; Sumida, Kazuki*; Tomohiro, Yuta*; Kusaka, Shotaro*; Okuyama, Yuma*; Ichinokura, Satoru*; Kobayashi, Masaki*; Takeda, Yukiharu; et al.
Nature Communications (Internet), 11, p.4821_1 - 4821_8, 2020/09
Times Cited Count：41 Percentile：93.11(Multidisciplinary Sciences)
-type ferromagnetic semiconductor (In,Fe)As:Be studied by X-ray magnetic circular dichroismSakamoto, Shoya*; Anh, L. D.*; Hai, P. N.*; Shibata, Goro*; Takeda, Yukiharu; Kobayashi, Masaki*; Takahashi, Yukio*; Koide, Tsuneharu*; Tanaka, Masaaki*; Fujimori, Atsushi*
Physical Review B, 93(3), p.035203_1 - 035203_6, 2016/01
Times Cited Count：18 Percentile：63.01(Materials Science, Multidisciplinary)-type ferromagnetic semiconductor (In,Fe)AsKobayashi, Masaki*; Anh, L. D.*; Hai, P. N.*; Takeda, Yukiharu; Sakamoto, Shoya*; Kadono, Toshiharu*; Okane, Tetsuo; Saito, Yuji; Yamagami, Hiroshi; Harada, Yoshihisa*; et al.
Applied Physics Letters, 105(3), p.032403_1 - 032403_4, 2014/07
Times Cited Count：6 Percentile：26.85(Physics, Applied)Kobayashi, Masaki*; Muneta, Iriya*; Takeda, Yukiharu; Harada, Yoshihisa*; Fujimori, Atsushi*; Krempask
, J.*; Schmitt, T.*; Oya, Shinobu*; Tanaka, Masaaki*; Oshima, Masaharu*; et al.
Physical Review B, 89(20), p.205204_1 - 205204_8, 2014/05
Times Cited Count：78 Percentile：92.27(Materials Science, Multidisciplinary)Niwa, Hideharu*; Saito, Makoto*; Kobayashi, Masaki*; Harada, Yoshihisa*; Oshima, Masaharu*; Moriya, Shogo*; Matsubayashi, Katsuyuki*; Nabae, Yuta*; Kuroki, Shigeki*; Ikeda, Takashi; et al.
Journal of Power Sources, 223, p.30 - 35, 2013/02
Times Cited Count：18 Percentile：50.94(Chemistry, Physical)To design non-platinum, inexpensive, but high performance carbon-based cathode catalysts for polymer electrolyte fuel cells, it is important to elucidate the active site for oxygen reduction reaction (ORR). However, it is difficult to directly identify the active site by applying conventional structural or electronic probes to such complex systems. Here, we used C 1
X-ray absorption spectroscopy (XAS) to observe electronic structure of carbon in iron phthalocyanine-based catalysts, and found a signature of edge exposure below the 
edge, whose intensity is well correlated with the ORR activity. These results demonstrate that C 1 XAS can be used to characterize the ORR activity of carbon-based cathode catalysts in terms of the edge exposure.
Kiuchi, Hisao*; Niwa, Hideharu*; Kobayashi, Masaki*; Harada, Yoshihisa*; Oshima, Masaharu*; Chokai, Masayuki*; Nabae, Yuta*; Kuroki, Shigeki*; Kakimoto, Masaaki*; Ikeda, Takashi; et al.
Electrochimica Acta, 82(1), p.291 - 295, 2012/10
Times Cited Count：14 Percentile：34.42(Electrochemistry)We study the characteristics of oxygen adsorption on metal-free carbon-based cathode catalysts derived from nitrogen-containing polyamide (PA) and nitrogen-free phenolic resin (PhRs). Electrochemical analysis and Raman spectroscopy showed higher 2-electron oxygen reduction reaction (ORR) activity and more defect sites in PA than PhRs. The increase in the amount of adsorbed oxygen in PA was also identified by oxygen adsorption isotherms. 
X-ray photoelectron spectroscopy reveals that graphite-like nitrogen contributes to oxygen adsorption and C=O components are dominant in PA. These experimental results indicate that the adsorbed C=O components near the graphite-like nitrogen can be assigned as active sites for 2-electron ORR.
Kobayashi, Masaki*; Niwa, Hideharu*; Saito, Makoto*; Harada, Yoshihisa*; Oshima, Masaharu*; Ofuchi, Hironori*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; et al.
Electrochimica Acta, 74, p.254 - 259, 2012/07
Times Cited Count：52 Percentile：80.98(Electrochemistry)The electronic structure of the residual metal atoms in FePc-based carbon catalysts, prepared by pyrolyzing a mixture of FePc and phenolic resin polymer at 800
C, before and after acid washing have been investigated using XAFS spectroscopy to clarify the role of Fe in the ORR activity. The decomposition analyses for the XAFS spectra reveal that the composition ratio of each Fe component is unaltered by the acid washing, indicating that the residual Fe components were removed by the acid washing irrespective of their chemical states. Because the oxygen reduction potential was approximately unchanged by the acid washing, the residual Fe itself does not seem to contribute directly to the ORR activity. The residual Fe can act as a catalyst to accelerate the growth of the sp
carbon network during pyrolysis. The results imply that light elements are components of the ORR active sites in the FePc-based carbon catalysts.
Kobayashi, Masaki*; Niwa, Hideharu*; Harada, Yoshihisa*; Horiba, Koji*; Oshima, Masaharu*; Ofuchi, Hironori*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; et al.
Journal of Power Sources, 196(20), p.8346 - 8351, 2011/10
Times Cited Count：32 Percentile：67.33(Chemistry, Physical)The electronic structure of Co atoms in CoPc-based carbon catalysts, which were prepared by pyrolyzing a mixture of CoPc and phenol resin polymer up to 1000
C, has been investigated using XAFS analysis and HXPES. The Co K XAFS spectra show that most of the Co atoms are in the metallic state and small quantities of oxidized Co components are present in the samples even after acid washing to remove Co atoms. Based on the difference in probing depth between XAFS and HXPES, it was found that after acid washing, the surface region with the aggregated Co clusters is primarily composed of metallic Co. Since the electrochemical properties remain almost unchanged even after the acid washing process, the residual metallic and oxidized Co atoms themselves will hardly contribute to the ORR activity of the CoPc-based carbon cathode catalysts, implying that the active sites of the CoPc-based catalysts primarily consist of light elements such as C and N.
Niwa, Hideharu*; Kobayashi, Masaki*; Horiba, Koji*; Harada, Yoshihisa*; Oshima, Masaharu*; Terakura, Kiyoyuki*; Ikeda, Takashi; Koshigoe, Yuka*; Ozaki, Junichi*; Miyata, Seizo*; et al.
Journal of Power Sources, 196(3), p.1006 - 1011, 2011/02
Times Cited Count：90 Percentile：91.52(Chemistry, Physical)We report on the electronic structure of three different types of N-containing carbon-based cathode catalysts for polymer electrolyte fuel cells observed by hard X-ray photoemission spectroscopy. C 1s spectra show the importance of 
carbon network formation for the oxygen reduction reaction (ORR) activity. Samples having high oxygen reduction reaction activity in terms of oxygen reduction potential contain high concentration of graphite-like nitrogen. Based on a quantitative analysis of our results, the oxygen reduction reaction activity of the carbon-based cathode catalysts will be improved by increasing concentration of graphite-like nitrogen in a developed carbon network.
Kataoka, Takashi*; Kobayashi, Masaki*; Sakamoto, Yuta*; Song, G. S.*; Fujimori, Atsushi*; Chang, F.-H.*; Lin, H.-J.*; Huang, D. J.*; Chen, C. T.*; Okochi, Takuo*; et al.
Journal of Applied Physics, 107(3), p.033718_1 - 033718_7, 2010/02
Times Cited Count：54 Percentile：86.13(Physics, Applied)CoOKobayashi, Masaki*; Ishida, Yukiaki*; Hwang, J. I.*; Osafune, Yoshitaka*; Fujimori, Atsushi*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Kobayashi, Keisuke*; Saeki, Hiromasa*; et al.
Physical Review B, 81(7), p.075204_1 - 075204_7, 2010/02
Times Cited Count：19 Percentile：61.85(Materials Science, Multidisciplinary)MnAs studied by X-ray magnetic circular dichroismTakeda, Yukiharu; Kobayashi, Masaki*; Okane, Tetsuo; Okochi, Takuo*; Okamoto, Jun*; Saito, Yuji; Kobayashi, Keisuke*; Yamagami, Hiroshi; Fujimori, Atsushi*; Tanaka, Arata*; et al.
Hoshako, 22(4), p.202 - 209, 2009/07
no abstracts in English
Kobayashi, Masaki*; Song, G.-S.*; Kataoka, Takashi*; Sakamoto, Yuta*; Fujimori, Atsushi; Okochi, Takuo*; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Yamagami, Hiroshi; et al.
Journal of Applied Physics, 105(12), p.122403_1 - 122403_4, 2009/06
Times Cited Count：12 Percentile：44.93(Physics, Applied) orbitals in the oxide-based diluted magnetic semiconductor In
VO
Kobayashi, Masaki*; Ishida, Yukiaki*; Hwang, J. I.*; Song, G. S.*; Takizawa, Masaru*; Fujimori, Atsushi; Takeda, Yukiharu; Okochi, Takuo*; Okane, Tetsuo; Saito, Yuji; et al.
Physical Review B, 79(20), p.205203_1 - 205203_5, 2009/05
Times Cited Count：7 Percentile：33.2(Materials Science, Multidisciplinary)FeO with hole dopingKobayashi, Masaki*; Hwang, J. I.*; Song, G.*; Oki, Yasuhiro*; Takizawa, Masaru*; Fujimori, Atsushi; Takeda, Yukiharu; Fujimori, Shinichi; Terai, Kota*; Okane, Tetsuo; et al.
Physical Review B, 78(15), p.155322_1 - 155322_4, 2008/10
Times Cited Count：5 Percentile：26.23(Materials Science, Multidisciplinary)
-SiCSong, G.*; Kobayashi, Masaki*; Hwang, J. I.*; Kataoka, Takashi*; Takizawa, Masaru*; Fujimori, Atsushi; Okochi, Takuo; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; et al.
Japanese Journal of Applied Physics, 47(9), p.7113 - 7116, 2008/09
Times Cited Count：3 Percentile：14.42(Physics, Applied)
