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Journal Articles

Reversible structure change in graphene/metal interface by intercalation and deintercalation

Fukaya, Yuki; Entani, Shiro*; Sakai, Seiji*

Physical Review B, 108(15), p.155422_1 - 155422_6, 2023/10

no abstracts in English

Journal Articles

Structural analysis of high-energy implanted Ni atoms into Si(100) by X-ray absorption fine structure spectroscopy

Entani, Shiro*; Sato, Shinichiro*; Honda, Mitsunori; Suzuki, Chihiro*; Taguchi, Tomitsugu*; Yamamoto, Shunya*; Oshima, Takeshi*

Radiation Physics and Chemistry, 199, p.110369_1 - 110369_7, 2022/10

 Times Cited Count:1 Percentile:33.72(Chemistry, Physical)

Ni silicide synthesis by Ni ion beam irradiation into Si attracts attention due to its advantages including the ability of formation of local structures, the controllability of ion beams, the formability of silicide without heat treatment and the high reproducibility of the resulting specimen. In this work, we investigate the local atomic structure of Si implanted with 3.0 MeV Ni$$^{+}$$ ions. Analysis of Ni K-edge fluorescent-yield extended X-ray absorption fine structure reveals that Ni atoms have mixed structure of metallic-like face-centered cubic Ni and NiSi$$_{2}$$ phases at the initial stage of the irradiation and the formation of NiSi$$_{2}$$ promotes significantly with the ion fluence above 10 $$^{15}$$ ions cm$$^{-2}$$. With consideration of the agreement between the ion fluence threshold for the structural transition and the critical Si-amorphization fluence, it is concluded that the amorphization of Si plays an important role in the synthesis of the NiSi$$_{2}$$ phase in Ni$$^{+}$$-irradiated Si.

Journal Articles

Synchrotron X-ray standing wave Characterization of atomic arrangement at interface between transferred graphene and $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001)

Entani, Shiro*; Honda, Mitsunori; Naramoto, Hiroshi*; Li, S.*; Sakai, Seiji*

Surface Science, 704, p.121749_1 - 121749_6, 2021/02

 Times Cited Count:3 Percentile:34.98(Chemistry, Physical)

Graphene is expected to be one of the most promising materials for nanoelectronics and spintronics. In most graphene-based devices, the graphene channel is placed on insulating substrates. Therefore, the study of inter-facial interactions between graphene and the insulator surface is of critical importance. In this study, the vertical arrangement of graphene which is transferred on $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001) has been studied by normal incidence X-ray standing wave (NIXSW) technique. The analysis of the NIXSW profile reveals that the graphene layer is located at 3.57 (${AA}$) above the $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001) surface, which is larger than the interlayer distance of graphite at 3.356 (${AA}$). Micro- Raman spectroscopy shows that the transferred graphene has a limited spatial distribution of hole concentration. The present study shows that transferred graphene on the sapphire substrate followed by vacuum-annealing has an atomically flat surface free from residual contaminations such as organic compounds and there occurs the hole-doping in graphene.

Journal Articles

Effective adsorption and collection of cesium from aqueous solution using graphene oxide grown on porous alumina

Entani, Shiro*; Honda, Mitsunori; Shimoyama, Iwao; Li, S.*; Naramoto, Hiroshi*; Yaita, Tsuyoshi; Sakai, Seiji*

Japanese Journal of Applied Physics, 57(4S), p.04FP04_1 - 04FP04_4, 2018/04

 Times Cited Count:3 Percentile:15(Physics, Applied)

Journal Articles

Spacing between graphene and metal substrates studied with total-reflection high-energy positron diffraction

Fukaya, Yuki; Entani, Shiro; Sakai, Seiji; Mochizuki, Izumi*; Wada, Ken*; Hyodo, Toshio*; Shamoto, Shinichi

Carbon, 103, p.1 - 4, 2016/07

 Times Cited Count:21 Percentile:59.56(Chemistry, Physical)

no abstracts in English

Journal Articles

Spin pumping blocked by single-layer graphene

Haku, Satoshi*; Tashiro, Takaharu*; Nakayama, Hiroyasu*; Ieda, Junichi; Entani, Shiro; Sakai, Seiji; Ando, Kazuya*

Applied Physics Express, 8(7), p.073009_1 - 073009_3, 2015/07

 Times Cited Count:5 Percentile:18.73(Physics, Applied)

We found that the spin pumping in a Ni$$_{81}$$Fe$$_{19}$$/Pt bilayer is strongly suppressed by inserting single-layer graphene (SLG) at the interface. The spin pumping in the Ni$$_{81}$$Fe$$_{19}$$/Pt bilayer enhances the magnetization damping of the ferromagnetic layer, which is quantified from microwave frequency dependence of ferromagnetic resonance linewidth. We show that the enhancement of the magnetization damping due to the spin pumping disappears in a Ni$$_{81}$$Fe$$_{19}$$/SLG/Pt trilayer. This result indicates that the spin pumping is blocked by the atomic monolayer, demonstrating the crucial role of the interfacial short-range spin-exchange coupling in the spin pumping in metallic systems.

Journal Articles

Magnetotransport properties of a few-layer graphene-ferromagnetic metal junctions in vertical spin valve devices

Entani, Shiro; Naramoto, Hiroshi*; Sakai, Seiji

Journal of Applied Physics, 117(17), p.17A334_1 - 17A334_4, 2015/05

 Times Cited Count:19 Percentile:63.98(Physics, Applied)

Journal Articles

Contracted interlayer distance in graphene/sapphire heterostructure

Entani, Shiro; Antipina, L. Y.*; Avramov, P.*; Otomo, Manabu*; Matsumoto, Yoshihiro*; Hirao, Norie; Shimoyama, Iwao; Naramoto, Hiroshi*; Baba, Yuji; Sorokin, P. B.*; et al.

Nano Research, 8(5), p.1535 - 1545, 2015/05

 Times Cited Count:24 Percentile:71.84(Chemistry, Physical)

Journal Articles

Contact-induced spin polarization in BNNT(CNT)/TM (TM=Co, Ni)nanocomposites

Kuzubov, A. A.*; Kovaleva, E. A.*; Avramov, P. V.*; Kuklin, A. V.*; Mikhaleva, N. S.*; Tomilin, F. N.*; Sakai, Seiji; Entani, Shiro; Matsumoto, Yoshihiro*; Naramoto, Hiroshi*

Journal of Applied Physics, 116(8), p.084309_1 - 084309_4, 2014/08

 Times Cited Count:9 Percentile:38.3(Physics, Applied)

Journal Articles

Atomic structure and physical properties of fused porphyrin nanoclusters

Avramov, P. V.*; Kuzubov, A. A.*; Sakai, Seiji; Otomo, Manabu*; Entani, Shiro; Matsumoto, Yoshihiro*; Eleseeva, N. S.*; Pomogaev, V. A.*; Naramoto, Hiroshi*

Journal of Porphyrins and Phthalocyanines, 18(7), p.552 - 568, 2014/07

 Times Cited Count:1 Percentile:5.31(Chemistry, Multidisciplinary)

Journal Articles

Contact-induced spin polarization of monolayer hexagonal boron nitride on Ni(111)

Otomo, Manabu; Yamauchi, Yasushi*; Kuzubov, A. A.*; Eliseeva, N. S.*; Avramov, P.*; Entani, Shiro; Matsumoto, Yoshihiro; Naramoto, Hiroshi*; Sakai, Seiji

Applied Physics Letters, 104(5), p.051604_1 - 051604_4, 2014/02

 Times Cited Count:12 Percentile:47.31(Physics, Applied)

Hexagonal boron nitride (h-BN) is a promising barrier material for graphene spintronics. In this study, spin-polarized metastable de-excitation spectroscopy (SPMDS) is employed to study the spin-dependent electronic structure of monolayer h-BN on Ni(111). The extreme surface sensitivity of SPMDS enables us to elucidate a partial filling of the in-gap states of h-BN without any superposition of Ni 3$$d$$ signals. The in-gap states are shown to have a considerable spin polarization parallel to the majority spin of Ni. The positive spin polarization is attributed to the $$pi$$-$$d$$ hybridization and the effective spin transfer to the nitrogen atoms at the h-BN/Ni(111) interface.

Journal Articles

Spin polarization of single-layer graphene epitaxially grown on Ni(111) thin film

Entani, Shiro; Kurahashi, Mitsunori*; Sun, X.*; Yamauchi, Yasushi*

Carbon, 61, p.134 - 139, 2013/09

 Times Cited Count:17 Percentile:49.29(Chemistry, Physical)

Journal Articles

Spin orientation transition across the single-layer graphene/nickel thin film interface

Matsumoto, Yoshihiro; Entani, Shiro; Koide, Akihiro*; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Amemiya, Kenta*; Fujikawa, Takashi*; Sakai, Seiji

Journal of Materials Chemistry C, 1(35), p.5533 - 5537, 2013/09

 Times Cited Count:32 Percentile:77.13(Materials Science, Multidisciplinary)

Journal Articles

High spin polarization at the Fe/C$$_{60}$$ interface in the Fe-doped C$$_{60}$$ film

Sakai, Seiji; Matsumoto, Yoshihiro; Otomo, Manabu; Entani, Shiro; Avramov, P.; Sorokin, P. B.*; Naramoto, Hiroshi*

Synthetic Metals, 173, p.22 - 25, 2013/06

 Times Cited Count:2 Percentile:10.36(Materials Science, Multidisciplinary)

Journal Articles

Contact-induced spin polarization in graphene/$$h$$-BN/Ni nanocomposites

Avramov, P.; Kuzubov, A. A.*; Sakai, Seiji; Otomo, Manabu; Entani, Shiro; Matsumoto, Yoshihiro; Naramoto, Hiroshi*; Eliseeva, N. S.*

Journal of Applied Physics, 112(11), p.114303_1 - 114303_10, 2012/12

 Times Cited Count:18 Percentile:59.58(Physics, Applied)

Journal Articles

Intrinsic edge asymmetry in narrow zigzag hexagonal heteroatomic nanoribbons causes their subtle uniform curvature

Avramov, P.; Fedorov, D. G.*; Sorokin, P. B.*; Sakai, Seiji; Entani, Shiro; Otomo, Manabu; Matsumoto, Yoshihiro; Naramoto, Hiroshi*

Journal of Physical Chemistry Letters (Internet), 3(15), p.2003 - 2008, 2012/08

 Times Cited Count:34 Percentile:79.62(Chemistry, Physical)

Journal Articles

High hydrogen-adsorption-rate material based on graphane decorated with alkali metals

Antipina, L. Y.*; Avramov, P.; Sakai, Seiji; Naramoto, Hiroshi*; Otomo, Manabu; Entani, Shiro; Matsumoto, Yoshihiro; Sorokin, P. B.*

Physical Review B, 86(8), p.085435_1 - 085435_7, 2012/08

 Times Cited Count:49 Percentile:86.64(Materials Science, Multidisciplinary)

Journal Articles

Bias voltage dependence of tunneling magnetoresistance in granular C$$_{60}$$-Co films with current-perpendicular-to-plane geometry

Sakai, Seiji; Mitani, Seiji*; Matsumoto, Yoshihiro; Entani, Shiro; Avramov, P.; Otomo, Manabu; Naramoto, Hiroshi*; Takanashi, Koki

Journal of Magnetism and Magnetic Materials, 324(12), p.1970 - 1974, 2012/06

 Times Cited Count:3 Percentile:14.95(Materials Science, Multidisciplinary)

Journal Articles

Structure determination of self-assembled monolayer on oxide surface by soft-X-ray standing wave

Baba, Yuji; Narita, Ayumi; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Hirao, Norie; Entani, Shiro; Sakai, Seiji

e-Journal of Surface Science and Nanotechnology (Internet), 10, p.69 - 73, 2012/04

We report on the first results for the geometrical determination of adsorbed atoms on an oxide by a soft-X-ray sanding wave method. The samples investigated were alkyl phosphonic acid (C10) adsorbed on a sapphire surface, which is one of the candidate systems for organic self-assembled monolayer (SAM) on oxides. The surface was irradiated by synchrotron soft X-rays from the surface normal. The intensity of photoelectrons was plotted as a function of the photon energy. We observed clear profiles of the photoelectron intensity due to the standing wave from the substrate. Compared with the simulation using the crystal parameters, it was found that the phosphorus atoms are located at 0.11 nm from the surface, while the constant height was not observed for carbon atoms. The results are in consistent with the results by XPS and NEXAFS; the molecules form SAM on the sapphire surface with phosphonic acids and alkyl chains are located at the upper side.

Journal Articles

Precise control of single- and bi-layer graphene growths on epitaxial Ni(111) thin films

Entani, Shiro; Matsumoto, Yoshihiro; Otomo, Manabu; Avramov, P.; Naramoto, Hiroshi*; Sakai, Seiji

Journal of Applied Physics, 111(6), p.064324_1 - 064324_6, 2012/03

 Times Cited Count:19 Percentile:62.83(Physics, Applied)

${it In-situ}$ analysis was performed on the graphene growth in ultrahigh vacuum chemical vapor deposition by exposing the epitaxial Ni(111) thin film to benzene vapor at 873 K. It is shown that the highly uniform single- and bi-layer graphenes can be synthesized by the control of benzene exposure in the range of 10-10$$^{5}$$ langmuirs, reflecting a change in the graphene growth-rate by three orders of magnitude in between the first and second layer. Electron energy loss spectroscopy measurements of single- and bi-layer graphenes indicates that the interface interaction between bi-layer graphene and Ni(111) is weakened in comparison with that between single-layer graphene and Ni(111). It is also clarified from the micro-Raman analysis that the structural and electrical uniformities of the graphene film transformed on a SiO$$_{2}$$ substrate are improved remarkably under the specific exposure conditions at which the growths of single- and bi-layer graphenes are completed.

144 (Records 1-20 displayed on this page)