著者

Okada Susumu Miyamoto Yoshiyuki Saito Mineo

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.64, no.24, pp.245405, 2001-11

被引用文献数

48 46

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We report on a first-principles total-energy calculation that provides the energetics and electronic structure of stable polymerized fullerites consisting of the smallest fullerene C20. We find that the C20 fullerene has periodic three-dimensional covalent networks with orthorhombic and tetragonal symmetries. Both are found to be energetically stable and to be elemental semiconductors with a moderate energy gap of about 1.5 eV. Substantially high peaks of the density of states are found to appear below the top of the valence band, suggesting that these materials under hole-doped conditions are candidates for superconductors.

著者

Okada Susumu Saito Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.64, no.20, pp.201303, 2001-10

被引用文献数

33 39

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We report first-principles total-energy electronic-structure calculations that provide energetics of encapsulation of C60 in nanotubes consisting of boron and nitrogen atoms and electronic structures of resulting “BNC peapods.” We find that the encapsulating process is exothermic for (10,10) and (9,9) nanotubes. The energy gain upon the encapsulation is larger than that for carbon peapods, so that the BN nanotube is a promising candidate to accommodate the fullerenes inside. The material is predicted to be a new form of ternary semiconductor with interesting structural hierarchy.

著者

Okada Susumu Saito Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.65, no.16, pp.165410, 2002-04

被引用文献数

74 83

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We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall distances are about 3 Å. The electronic energy bands around the Fermi energy depend interestingly on the tube radii due to the hybridization between σ and π states. We also find that the nearly-free-electron states of the nanotubes induce peculiar charge redistribution in the interwall region.

著者

Okada Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.72, no.15, pp.153409, 2005-10

被引用文献数

12 9

---

Total-energy electronic-structure calculations were performed to explore energetics and electronic structures of a one-dimensional array of C60 and potassium atoms encapsulated in metallic nanotubes. We find that the electron states of the potassium intercalated peapods depend on the number of potassium atoms intercalated. Intercalation induces substantial hybridization between pi electron states of C60 and the nanotube. The local density of states around the Fermi level shows that the potassium intercalated C60-peapod is a novel metal whose carriers are distributed on both the C60 and the nanotube.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.68, no.23, pp.235402, 2003-12

被引用文献数

26

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We report electronic structures and stabilities of rhombohedral C60 polymers by using the local spin-density approximation in the framework of the density-functional theory. Owing to hybrid networks of sp2-like (threefold coordinated) and sp3-like (fourfold coordinated) carbon atoms, the electronic structures of these polymers are considerably different from that of a face-centered cubic (fcc) C60. We find that polymerized structures attained at the double bonds are semiconducting whereas polymerized structures attained at single bonds are metallic. Significant overlap of the wave function in the space among three adjacent C60 causes the metallic behavior on the latter polymers. We also find that the stacking ordering strongly affects the conducting properties of the metallic polymers. Despite substantial density of states at Fermi level, the C60 polymers do not exhibit any magnetic ordering. Total energy calculations show that the metallic C60 polymers have higher total energy than the semiconducting C60 polymer phases.

著者

Okada Susumu Otani Minoru Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.67, no.20, pp.205411, 2003-05

被引用文献数

96 93

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We report total-energy electronic structure calculations that provide energetics of encapsulation of various fullerenes in carbon nanotubes and electronic structures of resulting carbon peapods. We find that the electron states of the peapods depend on the space in the nanotubes and that they reflect electron states of the encapsulated fullerenes. The deep energy position of the lowest unoccupied state of fullerenes as well as hybridization between π states of the fullerenes and the nearly free-electron states of the nanotubes causes a multicarrier character in the peapods.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.87, no.14, pp.146803, 2001-09

被引用文献数

333

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We report first-principles total-energy electronic-structure calculations in the density-functional theory performed for hexagonally bonded honeycomb sheets consisting of B, N, and C atoms. We find that the ground state of BNC sheets with particular stoichiometry is ferromagnetic. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic ordering, leading to an argument that the BNC sheet is a manifestation of the flat-band ferromagnetism.

著者

Otani Minoru Takagi Yoshiteru Koshino Mikito Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.96, no.24, pp.242504, 2010-06

被引用文献数

25

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Based on first-principle total-energy calculations, we have found that by applying an external electric field it is possible to control the magnetic state of graphite thin film with the rhombohedral stacking arrangement. When exposed to a moderate electric field normal to the film, the surface of a thin film of rhombohedral graphite undergoes a magnetic phase transition from the antiferromagnetic state to the ferromagnetic state. The polarized electron spin is primarily distributed in the bottommost layer of the film, which forms the interface with the negative electrode. The amount of polarized electron spin is calculated to be 0.067 μB/nm2. The ferromagnetic ordering with the characteristic distribution of the polarized electron spin opens the possibility of using graphite thin films in electronic devices with spin degree of freedom.

著者

岡田 進 朝日 良一 田島 なつき 隈崎 達夫 長谷川 節雄 菊池 洋史 上坂 伸宏 オカダ ススム アサヒ リョウイチ タジマ ナツキ クマザキ タツオ ハセガワ セツオ キクチ ヒロ シ ウエサカ ノブヒロ Okada Susumu Asahi Ryouichi Tajima Natsuki Kumazaki Tatsuo Hasegawa Setsuo Kikuchi Hiroshi Uyesaka Nobuhiro

出版者

日本医学放射線学会

雑誌

日本医学放射線学会雑誌 (ISSN:00480428)

巻号頁・発行日

vol.47, no.5, pp.729-744, 1987-05-25

著者

Konabe Satoru Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.102, no.11, pp.113110, 2013-03

被引用文献数

9 5

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We theoretically investigate the photocurrent generation efficiency of single-walled carbon nanotubes by considering the interplay between exciton many-body effects. We calculate the photocurrent by solving rate equations that incorporate the influences of the two competing processes, multiple exciton generation (MEG) and the Auger recombination (AR) processes. We find that MEG substantially enhances photocurrent generation in spite of the competing AR process. Our calculation shows that the generation efficiency is up to 150% higher than that without MEG.

著者

Yanagi Kazuhiro Moriya Rieko Cuong Nguyen Thanh Otani Minoru Okada Susumu

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.110, no.8, pp.086801, 2013-02

被引用文献数

18 1

---

We report clear experimental evidence for the charge manipulation of molecules encapsulated inside single-wall carbon nanotubes (SWCNTs) using electrochemical doping techniques. We encapsulated β-carotene (Car) inside SWCNTs and clarified electrochemical doping characteristics of their Raman spectra. C=C streching modes of encapsulated Car and a G band of SWCNTs showed clearly different doping behaviors as the electrochemical potentials were shifted. Electron extraction from encapsulated Car was clearly achieved. However, electrochemical characteristics of Car inside SWCNTs and doping mechanisms elucidated by calculations based on density-functional theory indicate the difficulty of charge manipulation of molecules inside SWCNTs due to the presence of strong on-site Coulomb repulsion energy at the molecules.

著者

Cuong Nguyen Thanh Otani Minoru Okada Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.87, no.4, pp.045424, 2013

被引用文献数

14 3

---

Based on first-principles total-energy calculations, we studied the energetics and electronic structure of zigzag graphene nanoribbons with nanometer-scale corners. We found that the formation energy of a short zigzag edge with a 120∘ corner is substantially smaller than that of a straight zigzag edge with an infinite length. We also found that zigzag graphene ribbons with 120∘ corners are semiconductors for which the band-gap decreases with increasing length between adjacent corners. The edge state is absent for zigzag graphene ribbons with short corner-corner distances, while the edge state emerges for zigzag ribbons that have a corner-corner distance greater than 1.5 nm. The remarkable stability of the 120∘ corner of the short zigzag edges is in good agreement with the experimental observation of such corners of graphene edges.

著者

Cuong Nguyen Thanh Otani Minoru Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.101, no.23, pp.233106, 2012-12

被引用文献数

10 1

---

Based on the first-principles total-energy calculations, we demonstrate the possibility of controlling the band-gap and carrier type of bilayer graphene using ionic molecules. Our calculations suggest that bilayer graphene sandwiched by a pair of cation-anion molecules is a semiconductor with a moderate energy gap of 0.26 eV that is attributable to the strong local dipole field induced by the cation-anion pair. Furthermore, we can control the semiconducting carrier type—intrinsic, p-type, or n-type—of bilayer graphene sandwiched by ionic molecules by changing the cation-anion pair.

著者

Okada Susumu Shiraishi Kenji Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.90, no.2, pp.026803, 2003-01

被引用文献数

33 21

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Based on total-energy electronic-structure calculations within the density-functional theory, we find that a high spin state is realized for an ultimate dangling bond unit on an otherwise hydrogen-covered Si(111) surface. We further propose a systematic method of constructing nanometer-scale dangling bond networks that exhibit the ferrimagnetic spin ordering. The interplay between the electron-electron interaction and the surface reconstruction is elucidated.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.91, no.21, pp.216801, 2003-11

被引用文献数

73 70

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We report total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled carbon nanotubes consisting of semiconducting (n,0) nanotubes. We find that optimum spacing between the walls of the nanotubes is slightly larger than the interlayer spacing of the graphite. We also find that the electronic structures of the double-walled nanotubes with the inner (7,0) nanotube are metallic with multicarrier characters in which electrons and holes exist on inner and outer nanotubes, respectively. Interwall spacing and curvature difference are found to be essential for the electron states around the Fermi level.

著者

Okada Susumu Oshiyama Atsushi

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.95, no.20, pp.206804, 2005-11

被引用文献数

45 43

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A total-energy electronic-structure calculation is performed to explore energetics and electronic structures of nanotubes adsorbed on metal surfaces. We find that the charge transfer from metal surfaces to the nanotubes takes place depending on both the electronic structures of the adsorbed nanotubes and the work functions of the metal surfaces. In addition, we also find a substantial hybridization between the electron states of metal atoms and those of the nanotubes, which results in the metal-induced inhomogeneous charge distribution in the nanotubes.

著者

Okada Susumu Nakada Kyoko Kawai Takazumi

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.19, no.36, pp.365231, 2007-09

被引用文献数

1

---

We study the electronic structure and energetics of carbon nanotubes with topological line defects consisting of fused pentagons and octagon rings by means of first-principles calculation in density functional theory and tight-binding molecular dynamics simulations. The tubes with the topological line defects are found to exhibit magnetic ordering where polarized electron spins are localized around the topological defect and ferromagnetically aligned along the defect. Our analyses of the electronic energy band and spin density distributions reveal that this ferromagnetic spin ordering is associated with the edge states that are inherent in the graphite ribbon with zigzag edges. The tight-binding molecular dynamics simulations show that the nanotubes with the topological line defects are thermally stable up to temperature of 3000 K and disrupted over 4000 K.

著者

Cuong Nguyen Thanh Otani Minoru Iizumi Yoko Okazaki Toshiya Rotas Georgios Tagmatarchis Nikos Li Yongfeng Kaneko Toshiro Hatakeyama Rikizo Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.99, no.5, pp.053105, 2011-08

被引用文献数

4 4

---

The transport properties of C59N encapsulated semiconducting single-walled carbon nanotubes (SWCNTs) (C59N-peapod) are investigated. Transport measurements of the peapods in field effect transistors (FETs) reveal that ∼14% of the C59N-peapod sample shows n-type behavior even though the electronic properties of the host SWCNTs are similar to those of C60-peapods that exhibit only p-type property. First-principles electronic-structure calculations reveal that the unique transport behavior originates from the monomer form of C59N encapsulated in SWCNTs. The singly occupied (SO) state of C59N lies in the energy gap of the SWCNT and the energy of this state increases substantially when electrons are injected. Because of this shift to higher energy, the SO state acts as a shallow donor state for the conduction band of the nanotube, which leads to n-type behavior in FET measurements.

著者

Konabe Satoru Okada Susumu

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.98, no.7, pp.073109, 2011-02

被引用文献数

4

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We propose a method for optically probing the magnetic states of metallic atoms encapsulated in single-walled carbon nanotubes. The absorption spectrum is calculated by solving the Bethe–Salpeter equation, which includes the effects of magnetic atoms, under the tight-binding approximation. Due to the exchange interaction between excitons and polarized spins in ferromagnets, triplet excitons acquire a finite oscillator strength and can thus be excited by light. This mechanism is promising for detecting magnetic ordering of materials encapsulated in carbon nanotubes.

著者

Kamiya Katsumasa Okada Susumu

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.83, no.15, pp.155444, 2011-04

被引用文献数

17 11

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We report total-energy electronic-structure calculations based on density functional theory performed on single-stranded DNA (ssDNA) encapsulated in single-walled carbon nanotubes (SWCNTs). We find that the encapsulation reaction is exothermic for nanotubes with diameters greater than 1.33 nm. The energy gain is calculated to be in the range of 0.8–1.5 eV/nm, depending on tube diameter, base sequences, and ssDNA structure. In optimal ssDNA-SWCNT hybrid-system geometries, the polar groups of ssDNA, i.e. the POH moiety in its backbone, are located adjacent to the wall of the nanotube. The electronic structure of the hybrid system is qualitatively similar to a simple sum of those of an isolated ssDNA molecule and an empty SWCNT. However, detailed analysis of the electronic structure of the hybrid system reveals that the encapsulation of ssDNA into a SWCNT affects the electronic structures of both the ssDNA and the SWCNT.