2021/12/21 更新

写真a

オバタ セイジ
小幡 誠司
OBATA Seiji
所属
異分野融合先端研究コア 准教授(特任)
職名
准教授(特任)
外部リンク

学位

  • 博士(理学) ( 2011年3月   東京大学理学系研究科化学専攻 )

  • 博士(理学) ( 東京大学 )

  • 修士(理学) ( 東京大学 )

研究分野

  • ナノテク・材料 / ナノ構造化学

 

論文

  • Tunable Chemical Coupling in Two-Dimensional van der Waals Electrostatic Heterostructures. 査読 国際誌

    Takaaki Taniguchi, Shisheng Li, Leanddas Nurdiwijayanto, Yu Kobayashi, Tetsuki Saito, Yasumitsu Miyata, Seiji Obata, Koichiro Saiki, Hiroyuki Yokoi, Kenji Watanabe, Takashi Taniguchi, Kazuhito Tsukagoshi, Yasuo Ebina, Takayoshi Sasaki, Minoru Osada

    ACS nano   13 ( 10 )   11214 - 11223   2019年10月

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    記述言語:英語  

    Heterostructures of two-dimensional (2D) atomic crystals provide fascinating molecular-scale design elements for emergent physical phenomena and functional materials, as integrating distinct monolayers into vertical heterostructures can afford coupling between disparate properties. However, the available examples have been limited to either van der Waals (vdW) or electrostatic (ES) heterostructures that are solely composed of noncharged and charged monolayers, respectively. Here, we propose a "vdW-ES heterostructure" chemical design in which charge-neutral and charged monolayer-building blocks with highly disparate chemical and physical properties are conjugated vertically through asymmetrically charged interfaces. We demonstrate vdW-ES heteroassembly of semiconducting MoS2 and dielectric Ca2Nb3O10- (CNO) monolayers using an amphipathic molecular starch, resulting in the emergence of trion luminescence observed at the lowest energy among MoS2-related materials, probably due to interfacial confinement effects given by vdW-ES dual interactions. In addition, interface engineering leads to tailored exciton of the vdW/ES heterostructures owing to the pronounced dielectric proximity effects, bringing an intriguing interlayer chemistry to modify 2D materials. Furthermore, the current approach was successfully extended to create a graphene/CNO heterostructure, which verifies the versatility of the preparative method.

    DOI: 10.1021/acsnano.9b04256

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  • Work Function Lowering of Graphite by Sequential Surface Modifications: Nitrogen and Hydrogen Plasma Treatment 査読

    赤田 圭史, 小幡 誠司, 斉木 幸一朗

    ACS OMEGA   2019年9月

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  • Effect of hydrogen on chemical vapor deposition growth of graphene on Au substrates 査読

    Terasawa Tomo-o, Taira Takanobu, Yasuda Satoshi, Obata Seiji, Saiki Koichiro, Asaoka Hidehito

    JAPANESE JOURNAL OF APPLIED PHYSICS   58   2019年8月

  • Size Separation of Graphene Oxide Using Alternating Current Electric Field 査読

    森本 健太, 小幡 誠司, 斉木 幸一朗

    Chem. lett.   48 ( 7 )   630 - 633   2019年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  • Analysis of the low-temperature restoration process of graphene oxide based on in-situ conductivity measurement 査読

    T. Shinohara, S. Obata, K. Saiki

    J. Mater. Chem. C   2019年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  • The effect of growth condition on graphene growth via Cu-assisted plasma reduction and restoration of graphene oxide 査読

    S. Obata, K. Saiki

    Jpn. J. Appl. Phys.   58 ( 015003 )   2019年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  • High degree reduction and restoration of graphene oxide on SiO2 at low temperature via remote Cu-assisted plasma treatment

    Seiji Obata, Minoru Sato, Keishi Akada, Koichiro Saiki

    Nanotechnology   29 ( 24 )   245603   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Institute of Physics Publishing  

    A high throughput synthesis method of graphene has been required for a long time to apply graphene to industrial applications. Of the various synthesis methods, the chemical exfoliation of graphite via graphene oxide (GO) is advantageous as far as productivity is concerned
    however, the quality of the graphene produced by this method is far inferior to that synthesized by other methods, such as chemical vapor deposition on metals. Developing an effective reduction and restoration method for GO on dielectric substrates has been therefore a key issue. Here, we present a method for changing GO deposited on a dielectric substrate into high crystallinity graphene at 550 °C
    this method uses CH4/H2 plasma and a Cu catalyst. We found that Cu remotely catalyzed the high degree reduction and restoration of GO on SiO2 and the effect ranged over at least 8 mm. With this method, field-effect transistor devices can be fabricated without any post treatment such as a transfer process. This plasma treatment increased electron and hole mobilities of GO to 480 cm2 V-1 s-1 and 460 cm2 V-1 s-1 respectively
    these values were more than 50 times greater than that of conventional reduced GO. Furthermore, the on-site conversion ensured that the shape of the GO sheets remained unchanged after the treatment. This plasma treatment realizes the high throughput synthesis of a desired shaped graphene on any substrate without any residue and damage being caused by the transfer process
    as such, it expands the potential applicability of graphene.

    DOI: 10.1088/1361-6528/aab73e

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  • An experimental study on impact-induced alterations of planetary organic simulants.

    Y. Sekine, K. Kodama, T. Kobayashi, S. Obata, Y. Chang, N. Ogawa, Y. Takano, N. Ohkouchi, K. Saiki, T. Sekine

    Meteoritics and Planetary Science   2018年

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  • Growth Temperature Dependence of Nitrogen Doped Graphene Structure on Pt (111) and Analysis of Its Reactivity with Oxygen 査読

    S.Obata, K. Saiki

    RSC Adv.   8   34309 - 34313   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

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  • Effect of grain boundaries in Cu foil on CVD growth of graphene

    Takanobu Taira, Seiji Obata, Koichiro Saiki

    APPLIED PHYSICS EXPRESS   10 ( 7 )   75503   2017年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    The effect of the grain boundaries (GBs) in a Cu foil on the CVD growth of graphene was investigated via radiation-mode optical microscopy, which we developed for the real-time observation of growing graphene domains. Although the GBs had the typical width and depth of a few micrometers and hundred nanometers, respectively, they had little effect on the nucleation and the lateral growth of the graphene domains. However, increasing the growth time caused the diffusion of C atoms from the inside of the Cu foil, which was likely to result in additive nucleation and the enhancement of the growth speed at the GBs. (c) 2017 The Japan Society of Applied Physics

    DOI: 10.7567/APEX.10.075503

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  • Nucleation site in CVD graphene growth investigated by radiation-mode optical microscopy

    Takanobu Taira, Seiji Obata, Koichiro Saiki

    APPLIED PHYSICS EXPRESS   10 ( 5 )   55502   2017年5月

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    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    DOI: 10.7567/APEX.10.055502

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  • 酸化グラフェン塗布膜の高次還元と高移動度化

    小幡 誠司, 佐藤 稔, 斉木 幸一朗

    Journal of the Vacuum Society of Japan   60 ( 8 )   300 - 306   2017年

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    記述言語:日本語  

    DOI: 10.3131/jvsj2.60.300

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  • Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field

    Kenji Kotsuki, Seiji Obata, Koichiro Saiki

    LANGMUIR   32 ( 2 )   644 - 649   2016年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand. Real-time observation of the SVA process revealed that rodlike single crystals grew with their long axes parallel to the electric field and bridged the prepatterned electrodes. As a result, C8-BTBT crystals automatically formed a field effect transistor (FET) structure and the mobility reached 1.9 cm(2)/(V s). Electric-field-assisted SVA proved a promising method for constructing high-mobility single-crystal FETs at the desired position by a low-cost solution process.

    DOI: 10.1021/acs.langmuir.5b03975

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  • Growth of N-doped graphene from nitrogen containing aromatic compounds: the effect of precursors on the doped site

    Tokio Katoh, Gaku Imamura, Seiji Obata, Koichiro Saiki

    RSC ADVANCES   6 ( 16 )   13392 - 13398   2016年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Doping of nitrogen into the graphene lattice tunes and tailors its electronic properties. To elucidate the doping mechanism and develop a method of controlling the doped structure, nitrogen doped graphene was synthesized from four kinds of nitrogen-containing aromatic compounds: quinoline, pyridine, pyrrole, and pyrimidine on Pt(111) at a variety of temperatures. The doped site and amount of nitrogen in the synthesized graphene depended considerably on the source molecule. Especially, nitrogen doped graphene with pyridinic-N and pyrrolic-N were predominantly obtained from quinoline and pyrrole sources. Comparison between the graphenes from different molecules indicated that structure and thermal stability of the source molecules together with their structural affinity to the honeycomb lattice determined the doping amount and the doped site.

    DOI: 10.1039/c5ra22664c

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  • 酸化グラフェンからの高結晶性グラフェン生成

    小幡 誠司

    炭素   275   171 - 181   2016年

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  • Graphene Oxide: A Fertile Nanosheet for Various Applications

    Obata, Seiji, Saiki, Koichiro, Taniguchi, Takaaki, Ihara, Toshihiro, Kitamura, Yusuke, Matsumoto, Yasumichi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   84 ( 12 )   121012   2015年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    Graphene oxide (GO) is chemically exfoliated graphene with various oxygen functional groups bound to its sp(2) basal plane. GO is not only a precursor for graphene in large-scale production but provides a fertile platform for applications from electronics to biology owing to its outstanding characteristics. In this review, we introduce the preparation and reduction methods and discuss recent application examples on electrochemistry and biological sensors.

    DOI: 10.7566/JPSJ.84.121012

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  • The influence of source molecule structure on the low temperature growth of nitrogen-doped graphene

    Tokio Katoh, Gaku Imamura, Seiji Obata, M. Bhanuchandra, Graeme Copley, Hideki Yorimitsu, Koichiro Saiki

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   17 ( 21 )   14115 - 14121   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Doping of heteroatoms such as nitrogen into the lattice structure of graphene can tune and tailor the overall electronic properties. N-doped graphene, depending on the nitrogen bonding mode and/or bonding configuration, displays subtly altered properties in comparison to pristine graphene. However, there remains a disappointing shortage of reliable methods for introducing dopants in a controlled and reproducible manner, preventing a thorough understanding of the relationship between structure and properties. In this study we aimed to prepare graphenes with nitrogen atoms doped at a graphitic (quaternary) site by depositing a source molecule containing a graphitic nitrogen atom: 4,4,8,8,12,12-hexamethyl-8,12-dihydro-4H-benzo[9,1]quinolizino[3,4,5,6,7-defg]acridine or 4H-benzo[9,1] quinolizino[3,4,5,6,7-defg] acridine-4,8,12-trione, on a heated Pt(111) substrate. At 400 degrees C, graphene with nitrogen atoms exclusively doped at a graphitic site was synthesized from the former molecule, while not from the latter molecule at any temperature. The present result indicates that the rational design of a source molecule is quite important for controlling the nitrogen doped site in the graphene lattice.

    DOI: 10.1039/c5cp02032h

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  • Electric-Field-Assisted Position and Orientation Control of Organic Single Crystals

    Kenji Kotsuki, Seiji Obata, Koichiro Saiki

    LANGMUIR   30 ( 47 )   14286 - 14291   2014年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We have investigated the motion of growing pentacene single crystals in solution under various electric fields. The pentacene single crystals in 1,2,4-trichlorobenzene responded to the electric field as if they were positively charged. By optimizing the strength and frequency of an alternating electric field, the pentacene crystals automatically bridged the electrodes on SiO2. The pentacene crystal with a large aspect ratio tended to direct the [1 10] orientation parallel to the conduction direction, which will be suitable from a viewpoint of anisotropy in mobility. The present result shows a possibility of controlling the position and orientation of organic single crystals by the use of an electric field, which leads to high throughput and low cost industrial manufacturing of the single crystal array from solution.

    DOI: 10.1021/la503286y

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  • The importance of spinning speed in fabrication of spin-coated organic thin film transistors: Film morphology and field effect mobility

    Kenji Kotsuki, Hiroshige Tanaka, Seiji Obata, Sven Stauss, Kazuo Terashima, Koichiro Saiki

    APPLIED PHYSICS LETTERS   104 ( 23 )   233306   2014年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    We have investigated the film morphology and the field effect mobility of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) thin films which were formed by spin coating on the SiO2 substrate with solution-processed graphene electrodes. The domain size and the density of aggregates in the C8-BTBT film showed the same dependence on the spinning speed. These competitive two factors (domain size and density of aggregates) give an optimum spinning speed, at which the field effect mobility of C8-BTBT transistor showed a maximum (2.6 cm(2)/V s). This result indicates the importance of spinning speed in the fabrication of solution processed organic thin film transistors by spin coating. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4883216

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  • Reduction of Graphene Oxide in Solution by Radical Treatment

    Hiroshige Tanaka, Seiji Obata, Koichiro Saiki

    CHEMISTRY LETTERS   43 ( 3 )   328 - 330   2014年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHEMICAL SOC JAPAN  

    Reduction of graphene oxide is a promising way for scalable production of graphene. The graphene reduced chemically from graphene oxide, however, retains many defects which were formed in the oxidation process, and thus its crystallinity is rather poor. Here, we report an effective reduction method of graphene oxide by radical treatment in solution. Graphene oxide was reduced more effectively by CH3I or BrC2H4Br than by hydrazine, which is a chemical reagent used for conventional reduction of graphene oxide. This radical reduction would facilitate large-scale production of graphene for various applications.

    DOI: 10.1246/cl.130918

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  • Control of work function of graphene by plasma assisted nitrogen doping

    Keishi Akada, Tomo-o Terasawa, Gaku Imamura, Seiji Obata, Koichiro Saiki

    APPLIED PHYSICS LETTERS   104 ( 13 )   131602   2014年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    Nitrogen doping is expected to provide several intriguing properties to graphene. Nitrogen plasma treatment to defect-free and defective highly oriented pyrolytic graphite (HOPG) samples causes doping of nitrogen atom into the graphene layer. Nitrogen atoms are initially doped at a graphitic site (inside the graphene) for the defect-free HOPG, while doping to a pyridinic or a pyrrolic site (edge of the graphene) is dominant for the defective HOPG. The work function of graphene correlates strongly with the site and amount of doped nitrogen. Nitrogen atoms doped at a graphitic site lower the work function, while nitrogen atoms at a pyridinic or a pyrrolic site increase the work function. Control of plasma treatment time and the amount of initial defect could change the work function of graphite from 4.3 eV to 5.4 eV, which would open a way to tailor the nature of graphene for various industrial applications. (C) 2014 AIP Publishing LLC.

    DOI: 10.1063/1.4870424

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  • Reduction of graphene oxide at the interface between a Ni layer and a SiO2 substrate

    Hiroshige Tanaka, Seiji Obata, Koichiro Saiki

    Carbon   59   472 - 478   2013年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Reduction of graphene oxide (GO) was carried out on SiO2 using a thin Ni overlayer as a catalyst. A Ni/GO/SiO2 structure was heated at 800 C in high vacuum for 6 min. After removing the Ni overlayer, formation of graphene was confirmed by Raman spectroscopy. For the Ni overlayer thinner than 40 nm, GO was reduced to graphene on-site. For the thicker Ni overlayer, however, GO was completely decomposed and graphene was formed in a segregation and/or precipitation process. The use of GO with a thin Ni overlayer enabled on-site and transfer-free fabrication of graphene without use of such flammable gases as methane and hydrogen. © 2013 Elsevier Ltd.

    DOI: 10.1016/j.carbon.2013.03.041

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  • Electrical and spectroscopic investigations on the reduction mechanism of graphene oxide

    Seiji Obata, Hiroshige Tanaka, Koichiro Saiki

    CARBON   55   126 - 132   2013年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Ultra-large graphene oxide sheets of monolayer thickness were obtained by removing ultrasonication during the conventional oxidation process of graphite. In situ electrical conductivity measurement during the reduction by hydrazine monohydrate vapor and thermal annealing revealed the existence of an onset temperature at which electrical conduction started to occur. Corresponding X-ray photoelectron spectra indicated that an approximately 65% restoration of the sp(2) network led to the occurrence of electrical conduction. Reduction by ring-opening of epoxide group by hydrazine treatment seemed to restore the sp(2) network, while thermal annealing left a considerable number of defects in the graphene sheet through the formation of volatile gases. (C) 2012 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.carbon.2012.12.018

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  • Conductive Atomic Force Microscopy of Chemically Synthesized Graphene Oxide and Interlayer Conduction

    Yoshio Kanamori, Seiji Obata, Koichiro Saiki

    CHEMISTRY LETTERS   40 ( 3 )   255 - 257   2011年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHEMICAL SOC JAPAN  

    Graphene oxide, a chemically modified graphene, has been attracting wide attention because of promising adaptability to a wide variety of applications. However, the properties of graphene oxide itself are not known well. Using a conductive cantilever, we observed a current image of graphene oxide nanosheets of various thicknesses. Current-voltage characteristics were found to reflect the local conductivity normal to the nanosheets. Under high electric fields, the conduction was well described in terms of Poole-Frenkel emission mechanism. The fitting of I-V curves to the Poole-Frenkel model provides information on dielectric properties, and the relative permittivity of graphene oxide was found to be 4.8 +/- 0.8.

    DOI: 10.1246/cl.2011.255

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  • Reduction of a Single Layer Graphene Oxide Film on Pt(111)

    Seiji Obata, Hiroshige Tanaka, Koichiro Saiki

    APPLIED PHYSICS EXPRESS   4 ( 2 )   25102   2011年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

    Graphene oxide (GO) is a very attractive material from which graphene of mass quantity could be fabricated. To restore the outstanding properties of graphene, however, complete reduction of GO is necessary, which no one has ever achieved before. We examined annealing of GO which was placed on Si(100) and Pt(111) and observed the surface atomic structure by scanning tunneling microscopy. A honeycomb lattice with long range order appeared for GO on Pt(111), but not for GO on Si(100). Reduction of GO together with restoration of the graphene lattice might be realized by the catalytic property of Pt, which opens a new way to synthesize graphene. (C) 2011 The Japan Society of Applied Physics

    DOI: 10.1143/APEX.4.025102

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  • Structure and properties of chemically prepared nanographene islands characterized by scanning tunneling microscopy

    Mayu Yamamoto, Seiji Obata, Koichiro Saiki

    SURFACE AND INTERFACE ANALYSIS   42 ( 10-11 )   1637 - 1641   2010年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JOHN WILEY & SONS LTD  

    Single-layer graphene islands with a typical diameter of several nanometers were grown on a Pt (111) substrate. Scanning tunneling microscopy (STM) analysis showed most of islands are hexagonally shaped and the zigzag-type edge predominates over the armchair-type edge. The apparent height at the atoms on the zigzag edge is enhanced with respect to the inside atoms for a small sample bias voltage, while such an enhancement was not observed at the atoms on the armchair edge. This result provides an experimental evidence of spatially (at the zigzag edge) and energetically (at the Fermi level) localized edge state in the nanographene islands, which were prepared chemically on Pt (111). Copyright (C) 2010 John Wiley & Sons, Ltd.

    DOI: 10.1002/sia.3583

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▼全件表示

MISC

  • 新規原料分子を用いたグラフェン及び窒素ドープグラフェンの成長

    加藤時穂, 今村岳, 小幡誠司, BHANUCHANDRA Malli, 依光英樹, 斉木幸一朗

    応用物理学会秋季学術講演会講演予稿集(CD-ROM)   75th   ROMBUNNO.19P-B3-14   2014年9月

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    記述言語:日本語  

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  • 26pJB-4 グラフェンおよび窒素ドープグラフェンの分子吸着特性(表面界面構造,領域9(表面・界面,結晶成長))

    小幡 誠司, 斉木 幸一朗

    日本物理学会講演概要集   68 ( 2 )   799 - 799   2013年8月

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    記述言語:日本語   出版者・発行元:一般社団法人日本物理学会  

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  • 19aEC-10 窒素ドープグラフェンの様々なドープ位置での酸素吸着特性(19aEC 領域7,領域9合同 グラフェン(分光・構造),領域7(分子性固体・有機導体))

    小幡 誠司, 斉木 幸一朗

    日本物理学会講演概要集   67 ( 2 )   770 - 770   2012年8月

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    記述言語:日本語   出版者・発行元:一般社団法人日本物理学会  

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