Language：English   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_2467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2018.1.0_3922

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Nitrogen doping is an effective method for modulating the electronic states and properties of graphene. In particular, chemical vapor deposition using nitrogen-containing organic molecules such as pyridine has been expected to be a facile way to control the doping site and amount of nitrogen. However, the atomic structure of nitrogen-doped graphene (NG) synthesized from such molecules has not been investigated. Furthermore, the nitrogen doping sites of NG synthesized at a high temperature of more than 1000 K have also not been measured. In this study, we carried out Scanning Tunneling Microscopy (STM) measurements on the structure of NG synthesized from pyridine, and elucidated the doping sites. Furthermore, we investigated how the doping of nitrogen atoms affects the reactivity with oxygen molecules to reveal the active site of a carbon alloy catalyst. We found that NG synthesized at 1150 K has nitrogen atoms doped into the pyridinic site, and these pyridinic sites enhance the reactivity to oxygen when comparing the defects with/without nitrogen. These findings will help with the synthesis of NG when controlling the doping sites and the development of a catalyst with high efficiency.

DOI： 10.1039/c8ra06962j

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.1.0_2425

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.73.2.0_1931

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2017.2.0_3780

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

DOI： 10.7567/APEX.10.055502

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2017.1.0_3857

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2017.1.0_3859

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Language：Japanese   Publisher：Vacuum Society of Japan  

Graphene: a monolayer sheet of graphite shows many attractive properties, which are expected to be applied to various devices. Development of a high throughput method has been required to realize the applications. Chemical exfoliation via graphene oxide (GO) has been considered one of the promising methods. However, the graphene reduced from GO showed poor crystallinity and mobility than that of mechanically exfoliated graphene. Many reduction methods have been investigated to obtain high mobility graphene from GO lately. In this review, we introduce a novel reduction method which we have developed to convert GO to graphene by explaining their advantages and some flaws to be solved.

DOI： 10.3131/jvsj2.60.300

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.2.0_3551

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.2.0_3553

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.1.0_3837

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.1.0_3839

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2016.1.0_3866

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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DOI： 10.7209/tanso.2016.171

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.2.0_3485

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.2.0_3358

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.2.0_2385

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.1.0_1474

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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2015.1.0_3679

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Publisher：The Surface Science Society of Japan  

DOI： 10.14886/sssj2008.35.0_78

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2014.2.0_3647

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：Japanese   Publisher：The Japan Society of Applied Physics  

DOI： 10.11470/jsapmeeting.2014.1.0_3733

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Publisher：公益社団法人 日本表面科学会  

CVD成長したグラフェンは、物性評価，応用などのために金属基板上からSiO₂/Si基板上への転写が必要である。本研究では、SiO₂/Si基板上に塗布した酸化グラフェン（GO）にCH₄/H₂の混合ガスプラズマを照射することで、絶縁基板上へのグラフェンの直接成長を試みた。GOへの20分間プラズマ照射により、通常のGOの還元では見られない鋭いラマン2Dピークが出現した。講演ではプラズマ照射条件がグラフェン成長に与える影響の詳細について発表する。

DOI： 10.14886/sssj2008.34.0_150

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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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