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

深谷 有喜; 圓谷 志郎; 境 誠司; 望月 出海*; 和田 健*; 兵頭 俊夫*; 社本 真一

Carbon, 103, p.1 - 4, 2016/07

 被引用回数:12 パーセンタイル:41.49(Chemistry, Physical)



Spin pumping blocked by single-layer graphene

白 怜士*; 田代 隆治*; 中山 裕康*; 家田 淳一; 圓谷 志郎; 境 誠司; 安藤 和也*

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

 被引用回数:3 パーセンタイル:79.6(Physics, Applied)



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

圓谷 志郎; 楢本 洋*; 境 誠司

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

 被引用回数:14 パーセンタイル:33.79(Physics, Applied)

Magnetotransport properties were studied for the vertical spin valve devices with two junctions of permalloy electrodes and a few-layer graphene interlayer. The graphene layer was directly grown on the bottom electrode by chemical vapor deposition. X-ray photoelectron spectroscopy showed that the permalloy surface fully covered with a few-layer graphene is kept free from oxidation and contamination even after dispensing and removing photoresist. This enabled fabrication of the current perpendicular to plane spin valve devices with a well-defined interface between graphene and permalloy. Spin-dependent electron transport measurements revealed a distinct spin valve effect in the devices. The magnetotransport ratio was 0.8% at room temperature and increased to 1.75% at 50 K. Linear current-voltage characteristics and resistance increase with temperature indicated that ohmic contacts are realized at the relevant interfaces.


Contracted interlayer distance in graphene/sapphire heterostructure

圓谷 志郎; Antipina, L. Y.*; Avramov, P.*; 大伴 真名歩*; 松本 吉弘*; 平尾 法恵; 下山 巖; 楢本 洋*; 馬場 祐治; Sorokin, P. B.*; et al.

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

 被引用回数:19 パーセンタイル:24.62(Chemistry, Physical)

Direct growth of graphene on insulators is expected to yield significant improvements in performance of graphene-based electronic and spintronic devices. In this study, we successfully reveal atomic arrangement and electronic properties of the coherent heterostructure of single-layer graphene and $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001). In the atomic arrangement analysis of single-layer graphene on $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001), we observed apparently contradicting results. The in-plane analysis shows that single-layer graphene grows not in the single-crystalline epitaxial manner but in the polycrystalline form with two strongly pronounced preferred orientations. This suggests the relatively weak interfacial interactions to be operative. But, we demonstrate that there exists unusually strong physical interactions between graphene and $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001), as evidenced by the short vertical distance between graphene and $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001) surface. The interfacial interactions are shown to be dominated by the electrostatic force involved in the graphene $$pi$$-system and the unsaturated electrons of the topmost O layer of $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001) rather than the van der Waals interactions. Such feature causes hole doping into graphene, which gives graphene a chance to slide on the $$alpha$$-Al$$_{2}$$O$$_{3}$$(0001) surface with a small energy barrier despite the strong interfacial interactions.


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.*; 境 誠司; 圓谷 志郎; 松本 吉弘*; 楢本 洋*

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

 被引用回数:8 パーセンタイル:55.31(Physics, Applied)

The interaction between carbon and BN nanotubes (NT) and transition metal Co and Ni supports was studied using electronic structure calculations. Several configurations of interfaces were considered, and the most stable ones were used for electronic structure analysis. All NT/Co interfaces were found to be more energetically favorable than NT/Ni, and conductive carbon nanotubes demonstrates lightly stronger bonding than semiconducting ones. The presence of contact-induced spin polarization was established for all nanocomposites. It was found that the contact-induced polarization of BNNT leads to the appearance of local conductivity in the vicinity of the interface while the rest of the nanotube lattice remains to be insulating.


Atomic structure and physical properties of fused porphyrin nanoclusters

Avramov, P. V.*; Kuzubov, A. A.*; 境 誠司; 大伴 真名歩*; 圓谷 志郎; 松本 吉弘*; Eleseeva, N. S.*; Pomogaev, V. A.*; 楢本 洋*

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

 被引用回数:1 パーセンタイル:100(Chemistry, Multidisciplinary)

A wide variety of planar and curved fused porphyrin/metalloporphyrin nanoclusters have been studied at the LC-GGA DFT level. It was found that curved and hollow-caged 0D and 1D nanoclusters are metastable and bear unique atomic and electronic structure and mechanical properties. Under different types of mechanical loads the nanoclusters display ultrastrong and superelastic properties. The curvature of the hollow cage nanoclusters leads to the redistribution of the metal d states near the Fermi level. The extremely high spin states allow one to use Fe-porphyrin nanoclusters as molecular supermagnets and logic quantum gates for holonomic quantum computations.


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

大伴 真名歩; 山内 泰*; Kuzubov, A. A.*; Eliseeva, N. S.*; Avramov, P.*; 圓谷 志郎; 松本 吉弘; 楢本 洋*; 境 誠司

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

 被引用回数:10 パーセンタイル:47.93(Physics, Applied)

六方晶窒化ホウ素(h-BN)はグラフェン・スピントロニクスのトンネルバリア材料として有望視されている。本研究ではスピン偏極準安定ヘリウム脱励起分光法(SPMDS)を用いて、Ni(111)上の単層h-BNのスピン分解バンド構造を調べた。SPMDSの最表面敏感性により、Ni 3$$d$$ピークの重複を受けずに部分的に占有されたギャップ内順位を検出できた。さらにこのギャップ内順位は大きなスピン偏極を持ち、Niの多数スピン側に偏極していることが示された。この正のスピン偏極は、h-BN/Ni(111)界面における$$pi$$-$$d$$軌道混成によるものであると帰属できた。


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

圓谷 志郎; 倉橋 光紀*; Sun, X.*; 山内 泰*

Carbon, 61, p.134 - 139, 2013/09

 被引用回数:16 パーセンタイル:44.81(Chemistry, Physical)

The spin-resolved electronic structure of graphene on Ni(111) was investigated using spin-polarized metastable deexcitation spectroscopy (SPMDS). Graphene was grown epitaxially on a Ni(111) single-crystalline surface using the ultra high vacuum chemical vapor deposition technique with benzene vapor as a precursor. At 50 L (5$$times$$10$$^{-5}$$ Torr sec), a single epitaxial layer of graphene was formed, but no further growth was observed at higher exposure. The spin-summed spectrum of graphene/Ni(111) had a new peak at the Fermi level and three weak features corresponding to the molecular orbitals of graphene. Spin asymmetry analysis of the SPMDS spectra revealed that the spin polarization of the electronic states shown by the new peak was parallel to the majority spin of the Ni substrate. The appearance and spin polarization of the new electronic states are discussed in terms of the hybridization of graphene pi orbitals and Ni d orbitals.


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

松本 吉弘; 圓谷 志郎; 小出 明広*; 大伴 真名歩; Avramov, P.; 楢本 洋*; 雨宮 健太*; 藤川 高志*; 境 誠司

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

 被引用回数:20 パーセンタイル:27.59(Materials Science, Multidisciplinary)

The spin-electronic structures across the interface between single-layer graphene and a Ni(111) thin film are explored by employing the depth-resolved X-ray absorption and magnetic circular dichroism spectroscopy with the atomic layer resolution. The depth-resolved Ni L-edge analysis clarifies that the Ni atomic layers adjacent to the interface show a transition of the spin orientation to the perpendicular one in contrast with the in-plane one in the bulk region. The C K-edge analysis reveals the intensifying of the spin-orbital interactions induced by the $$Pi$$-d hybridization at the interface as well as out-of-plane spin polarization at the $$Pi$$ band region of graphene. The present study indicates the importance of the interface design at the atomic layer level for graphene-based spintronics.


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

境 誠司; 松本 吉弘; 大伴 真名歩; 圓谷 志郎; Avramov, P.; Sorokin, P. B.*; 楢本 洋*

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

 被引用回数:2 パーセンタイル:86.7(Materials Science, Multidisciplinary)

A process of tunneling conduction and the spin-dependent resistivity change (so-called tunneling magnetoresitance effect) in the Fe-doped C$$_{60}$$ film with a granular structure is investigated for the current-into-plane device. Cooperative tunneling (cotunneling) through several Fe nanoparticles is suggested to be operative at temperatures lower than 20 K. By considering the effect of cotunneling on the magnetoresistance ratio, it is successfully shown that the spin polarization of tunneling electrons generated at the Fe/C$$_{60}$$ interface is much higher than that in Fe crystal at low temperature in a similar fashion to that at the Co/C$$_{60}$$ interface in the Co-doped C$$_{60}$$ films. A strong temperature dependence of spin polarization is observed, suggesting possible influences by the thermally-induced disorders ascribed in the Fe atoms bonded with C$$_{60}$$ in the C$$_{60}$$-Fe compound.


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

Avramov, P.; Kuzubov, A. A.*; 境 誠司; 大伴 真名歩; 圓谷 志郎; 松本 吉弘; 楢本 洋*; Eliseeva, N. S.*

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

 被引用回数:14 パーセンタイル:41.1(Physics, Applied)

Atomic and electronic structure of graphene/Ni(111), $$h$$-BN/Ni(111) and graphene/$$h$$-BN/Ni(111) nanocomposites with different numbers of graphene and $$h$$-BN layers and in different mutual arrangements of graphene/Ni and $$h$$-BN/Ni at the interfaces was studied using LDA/PBC/PW technique. For the sake of comparison, corresponding graphene, $$h$$-BN and graphene/$$h$$-BN structures without the Ni plate were calculated using the same technique. It was suggested that C-$$top$$:C-$$fcc$$ and N-$$top$$:B-$$fcc$$ configurations are energetically favorable for the graphene/Ni and $$h$$-BN/Ni interfaces, respectively. The Ni plate was found to induce a significant degree of spin polarization in graphene and $$h$$-BN caused by direct exchange interactions of the electronic states located on different fragments.


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

Avramov, P.; Fedorov, D. G.*; Sorokin, P. B.*; 境 誠司; 圓谷 志郎; 大伴 真名歩; 松本 吉弘; 楢本 洋*

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

 被引用回数:28 パーセンタイル:20.41(Chemistry, Physical)

The atomic and electronic structure of narrow zigzag nanoribbons with finite length, consisting of graphene terminated by fluorine on one side, hexagonal ($$h$$)-BN, and $$h$$-SiC were studied with density functional theory. It is found that the asymmetry of nanoribbon edges causes a uniform curvature of the ribbons due to structural stress in the aromatic ring plane. Narrow graphene nanoribbons terminated with fluorine on one side demonstrate a considerable out-of-plane bend, suggesting that the nanoribbon is a fraction of a conical surface. It is shown that the intrinsic curvature of the narrow nanoribbons destroys the periodicity and results in a systematic cancellation of the dipole moment. The in- and out-of-plane curvature of thin arcs allows their closure in nanorings or cone fragments of giant diameter.


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

Antipina, L. Y.*; Avramov, P.; 境 誠司; 楢本 洋*; 大伴 真名歩; 圓谷 志郎; 松本 吉弘; Sorokin, P. B.*

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

 被引用回数:41 パーセンタイル:12.39(Materials Science, Multidisciplinary)

The graphane with chemically bonded alkali metals (Li, Na, K) was considered as potential material for hydrogen storage. The ab initio calculations show that such material can adsorb as many as four hydrogen molecules per Li, Na, and K metal atom. These values correspond to 12.20, 10.33, and 8.56 wt% of hydrogen, respectively, and exceed the DOE requirements. The thermodynamic analysis shows that Li-graphane complex is the most promising for hydrogen storage with ability to adsorb three hydrogen molecules per metal atom at 300 K and pressure in the range of 5-250 atm.


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

境 誠司; 三谷 誠司*; 松本 吉弘; 圓谷 志郎; Avramov, P.; 大伴 真名歩; 楢本 洋*; 高梨 弘毅

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

 被引用回数:3 パーセンタイル:82.11(Materials Science, Multidisciplinary)

Voltage-dependence of the tunneling magnetoresistance effect in the granular C$$_{60}$$-Co films has been investigated under the current-perpendicular-to-plane geometry. The transport measurements demonstrate that the granular C$$_{60}$$-Co films show unusually an exponential MR-V dependence. Small characteristic energies of less than 10's meV are derived from the temperature dependences of the characteristic voltage in the exponential relationship. Considering the voltage drops between Co nanoparticles and also the effect of cotunneling on the energy values, the characteristic energies for the voltage-induced degradation of the spin polarization are found to show a satisfactory agreement with that for the thermally-induced one. It can reasonably be expected that the onset of magnetic disorder to the localized d-electron spins at the interface region of the C$$_{60}$$-Co compound with Co nanoparticles will lead to the unusual voltage and temperature dependence of the MR ratio and the spin polarization.


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

馬場 祐治; 成田 あゆみ; 関口 哲弘; 下山 巖; 平尾 法恵; 圓谷 志郎; 境 誠司

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



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

圓谷 志郎; 松本 吉弘; 大伴 真名歩; Avramov, P.; 楢本 洋*; 境 誠司

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

 被引用回数:15 パーセンタイル:38.79(Physics, Applied)



Local structures and magnetic properties of fullerene-Co systems studied by XAFS and XMCD analyses

北条 育子*; 小出 明広*; 松本 吉弘; 丸山 喬*; 永松 伸一*; 圓谷 志郎; 境 誠司; 藤川 高志*

Journal of Electron Spectroscopy and Related Phenomena, 185(1-2), p.32 - 38, 2012/03

 被引用回数:1 パーセンタイル:90.87(Spectroscopy)

In this work we have measured Co K- and L$$_{2,3}$$-edge X-ray absorption near edge structure (XANES) and Co L$$_{2,3}$$-edge X-ray magnetic circular dichroism (XMCD) spectra, and also carried out their calculations for C$$_{60}$$Co$$_x$$ compounds. The observed XANES and XMCD are sensitive to the Co concentration. In the low density region ($$x$$=1.0-1.5), one Co is surrounded by three C$$_{60}$$ balls. The Co L$$_{2,3}$$-edge XMCD analyses gives the spin magnetic moment on Co in the range 0.5-0.9 $$mu_B$$.


Quasi-monochromatic pencil beam of laser-driven protons generated using a conical cavity target holder

西内 満美子; Pirozhkov, A. S.; 榊 泰直; 小倉 浩一; Esirkepov, T. Z.; 谷本 壮; 金崎 真聡; 余語 覚文; 堀 利彦; 匂坂 明人; et al.

Physics of Plasmas, 19(3), p.030706_1 - 030706_4, 2012/03

 被引用回数:6 パーセンタイル:67.57(Physics, Fluids & Plasmas)

2J 60fsのチタンサファイアレーザー光を、コニカル形状を持ったターゲットホルダに装着したターゲットに照射することによって、7MeVのコリメートされた陽子線($$10^6$$個/spot)を生成することに成功した。ターゲットホルダ上に陽子に前駆して発生する電子によって生成される電場が陽子線の軌道を変え、エネルギー選択をも行うと考えられる。


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

馬場 祐治; 成田 あゆみ; 関口 哲弘; 下山 巖; 平尾 法恵; 圓谷 志郎; 境 誠司

Photon Factory Activity Report 2011, Part B, P. 201, 2012/00



Ferromagnetic interlayer coupling in C$$_{60}$$-Co compound/Ni bilayer structure

松本 吉弘; 境 誠司; 圓谷 志郎; 高木 康多*; 中川 剛志*; 楢本 洋*; Avramov, P.; 横山 利彦*

Chemical Physics Letters, 511(1-3), p.68 - 72, 2011/07

 被引用回数:5 パーセンタイル:80.03(Chemistry, Physical)

C$$_{60}$$-Co化合物/Niの二層構造の電子・スピン状態についてX線磁気円二色性(XMCD)を用いた分光解析を行った。結果としてNi(111)表面上のC$$_{60}$$-Co化合物(数nm厚)では、Niの残留磁化のみで、局在スピン(Co dスピン)由来の強いXMCD信号が観測された。これはNi界面から3nm程度のC$$_{60}$$-Co化合物領域が、恐らく層間の電荷移動に関係のあるC$$_{60}$$分子を介した間接的交換相互作用により、下地のNiと強磁性的にカップリングしていることを指し示している。

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