Hiroyuki Muramatsu

Nagaoka University of Technology, Нагаока, Niigata, Japan

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Publications (113)521.24 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: A new synthetic method is demonstrated for transforming rice husks into bulk amounts of graphene through its calcination and chemical activation. The bulk sample consists of crystalline nano-sized graphene and corrugated individual graphene sheets; the material generally contains one, two, or a few layers, and corrugated graphene domains are typically observed in monolayers containing topological defects within the hexagonal lattice and edges. Both types of graphenes exhibit atomically smooth surfaces and edges.
    Small 03/2014; · 7.82 Impact Factor
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    ABSTRACT: Resonant Raman spectroscopy studies are performed to access information about the intertube interactions and wall-to-wall distances in double- and triple-walled carbon nanotubes. Here, we explain how the surroundings of the nanotubes in a multi-walled system influence their radial breathing modes. Of particular interest, the innermost tubes in double- and triple-walled carbon nanotube systems are shown to be significantly shielded from environmental interactions, except for those coming from the intertube interaction with their own respective host tubes. From a comparison of the Raman results for bundled as well as individual fullerene-peapod-derived double- and triple-walled carbon nanotubes, we observe that metallic innermost tubes, when compared to their semiconducting counterparts, clearly show weaker intertube interactions. Additionally, we discuss a correlation between the wall-to-wall distances and the frequency upshifts of the radial breathing modes observed for the innermost tubes in individual double- and triple-walled carbon nanotubes. All results allow us to contemplate fundamental properties related to DWNTs and TWNTs, as for example diameter- and chirality-dependent intertube interactions. We also discuss differences in fullerene-peapod-derived and chemical vapor deposition grown double- and triple-walled systems with the focus on mechanical coupling and interference effects.
    ACS Nano 01/2014; · 12.06 Impact Factor
  • Journal of CO2 Utilization. 01/2014; 5:60–65.
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    ABSTRACT: We report the preparation of hybrid paper-like films consisting of alternating layers of graphene (or graphene oxide) and different types of multi-walled carbon nanotubes (N-doped MWNTs, B-doped MWNTs and pristine MWNTs). We used an efficient self-assembly method in which nanotubes were functionalized with cationic polyelectrolytes in order to make them dispersible in water, and subsequently these suspensions were mixed with graphene oxide (GO) suspensions, and the films were formed by casting/evaporation processes. The electronic properties of these films (as produced and thermally reduced) were characterized and we found electrical resistivities as low as 3x10(-4) Ω cm. Furthermore, we observed that these films could be used as electron field emission sources with extraordinary efficiencies; threshold electric field ca. 0.55 V/μm, β factor as high as of 15.19x10(3) and operating currents up to 220 µA. These values are significantly enhanced when compared to previous reports in the literature for other carbon nanostructured film-like materials. We believe these hybrid foils could find other applications as scaffolds for tissue regeneration, thermal and conducting papers and laminate composites with epoxy resins.
    ACS Nano 11/2013; · 12.06 Impact Factor
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    ABSTRACT: Chemical stability of 6-coodinated SrO is a fundamental problem when this is used for various applications. In this study, optical and chemical stabilities of 8-coordinated SrO:Eu2+ phosphor were investigated. SrO:Eu2+ phosphor was synthesized from thermal treatment of SrO:Eu powder located on a single crystalline MgO at 1500° C under reduction atmosphere. Obtained 8-coordinated SrO:Eu2+ phosphor exhibit strong blue luminescence and chemical stability in distilled water for 3 days. Our findings prove that obtained 8-coordinated SrO:Eu2+ possesses relative optical and chemical stabilities in water.
    Journal of Solid State Chemistry 08/2013; · 2.04 Impact Factor
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    ABSTRACT: We have used in situ current-voltage measurements of cup-stacked carbon nanotubes (CSCNTs) to establish reversible strain induced (compressive bending) semiconducting to metallic behavior. The corresponding electrical resistance decreases by two orders of magnitude during the process, and reaches values comparable to those of highly crystalline multi-walled carbon nanotubes (MWCNTs) and graphite. Joule heating experiments on the same CSCNTs showed that the edges of individual cups merge to form "loops" induced by the heating process. The resistance of these looped CSCNTs was close to that of highly deformed CSCNTs (and crystalline MWCNTs), thus suggesting that a similar conduction mechanism took place in both cases. Using a combination of molecular dynamics and first-principles calculations based on density functional theory, we conclude that an edge-to-edge interlayer transport mechanism results in conduction channels at the compressed side of the CSCNTs due to electronic density overlap between individual cups, thus making CSCNTs more conducting. This strain-induced CSCNT semiconductor to metal transition could potentially be applied to enable functional composite materials (e.g. mechanical sensors) with enhanced and tunable conducting properties upon compression.
    Nanoscale 07/2013; · 6.23 Impact Factor
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    ABSTRACT: Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.
    Nature Communications 07/2013; 4:2162. · 10.02 Impact Factor
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    ABSTRACT: We have demonstrated the ability to control the interlayer spacing of scrolled reduced graphene nanotubes through a high-temperature thermal treatment. The thermal annealing-induced variation of the interlayer spacing from 0.385 to 0.339 nm allowed us to study the change in the electronic and transport properties of the scrolled tubes.
    RSC Advances 03/2013; 3(13):4161-4166. · 2.56 Impact Factor
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    ABSTRACT: In this work, we carried out chemical oxidation studies of nitrogen-doped multiwalled carbon nanotubes (CNx-MWCNTs) using potassium permanganate in order to obtain nitrogen-doped graphene nanoribbons. Reaction parameters such as oxidation reaction, reaction time, the oxidizer to nanotube mass ratio, and the temperature were varied, and their effect was carefully analyzed. The presence of nitrogen atoms makes CNx-MWCNTs more reactive toward oxidation when compared to undoped multiwalled carbon nanotubes (MWCNTs). High-resolution transmission electron microscopy studies indicate that the oxidation of the graphitic layers within CNx-MWCNTs results in the unzipping of large diameter nanotubes and the formation of a disordered oxidized carbon coating on small diameter nanotubes. The nitrogen content within unzipped CNx-MWCNTs decreased as a function of the oxidation time, temperature, and oxidizer concentration. By controlling the degree of oxidation, the N atomic % could be reduced from 1.56% in pristine CNx-MWCNTs down to 0.31 atom % in nitrogen-doped oxidized graphene nanoribbons. A comparative thermogravimetric analysis reveals a lower thermal stability of the (unzipped) oxidized CNx-MWCNTs when compared to MWCNT samples. The oxidized graphene nanoribbons were chemically and thermally reduced and yielded nitrogen-doped graphene nanoribbons (N-GNRs). The thermal reduction at relatively low temperature (300 °C) results in graphene nanoribbons with 0.37 atom % of nitrogen. This method represents a novel route to preparation of bulk quantities of nitrogen-doped unzipped carbon nanotubes, which is able to control the doping level in the resulting reduced GNR samples. Finally, the electrochemical properties of these materials were evaluated.
    ACS Nano 03/2013; · 12.06 Impact Factor
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    ABSTRACT: The optical characterization of bundled and individual triple-walled carbon nanotubes was studied for the first time in detail by using resonant Raman spectroscopy. In our approach, the outer tube of a triple-walled carbon nanotube system protects the two inner tubes (or equivalently the inner double-walled carbon nanotube) from external environment interactions making them a partially isolated system. Following the spectral changes and line-widths of the radial breathing modes and G-band by performing laser energy dependent Raman spectroscopy, it is possible to extract important information as regards the electronic and vibrational properties, tube diameters, wall-to-wall distances, radial breathing mode and G-band resonance evolutions and high-curvature inter-tube interactions in isolated double- and triple-walled carbon nanotube systems.
    ACS Nano 01/2013; · 12.06 Impact Factor
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    ABSTRACT: The fascinating characteristic of carbon atoms to create multiple orbital hybridizations (e.g., sp, sp2, or sp3) provides the possibility to synthesize one-, two-, and three-dimensional carbon nanostructures with unique physical–chemical properties. In this way, the two-dimensional (2D) carbon-atomic layered crystal (graphene) and graphitic nanoribbons have attracted the attention of several scientific groups around the world due to their novel and unusual physicochemical properties. The relative simplicity of the Novoselov–Geim method to extract a single graphene layer along with the fascinating properties of graphene, such as the linear E(k) electronic structure in monolayer graphene, has stimulated extensive experimental and theoretical studies. This chapter reviews experimental and theoretical work on graphene with special attention to graphene nanoribbons. We focus on the role of topological defects, edge chirality, and chemical doping on the electronic, transport, and structural properties of graphene and graphene nanoribbons. We also review different synthesis techniques, such as chemical vapor deposition, chemical routes, and nanotube exfoliation, to obtain carbon nanoribbons. We also summarize common characterization techniques used for graphene materials, such as scanning electron microscopy, high resolution electron microscopy, scanning tunneling spectroscopy, near edge X-ray absorption fine structure, electron spin resonance, and Raman spectroscopy techniques. Edge-state characterization and the special magnetic properties of edges are also reviewed. In addition, first-principles density functional theory calculations of the electronic and transport properties of doped armchair nanoribbons are described. Finally, we discuss the future perspectives of these graphene-like materials, including applications in electronic devices, composites, catalysts, and energy storage devices.
    01/2013: pages 61–87; , ISBN: 978-0-12-385469-8
  • Journal of Raman Spectroscopy 12/2012; 43(12):1951-1956. · 2.68 Impact Factor
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    ABSTRACT: The vibrational and structural properties of modified double-wall carbon nanotubes (DWNTs) were investigated by high-pressure resonance Raman scattering. We studied bromine-intercalated DWNTs grown by chemical vapor deposition (CVD) and 13 C 60 peapod-derived DWNTs in comparison with pristine CVD-grown DWNTs. The effects of chemical modification, carbon interwall geometry, and inhomogeneous filling on the high-pressure evolution of the DWNTs have been investigated. We find that the mechanical resistance of the DWNT system is affected both in the case of bromine-intercalated CVD-DWNTs and also for the 13 C 60 peapod-derived DWNTs, thus lowering the onset of collapse pressure P (onset) c compared with pristine CVD-DWNTs. For bromine CVD-DWNTs, P (onset) c was observed to be 13 GPa, well below the 21 GPa found for pristine CVD-DWNTs. Uniaxial constrains in the interstitial regions of the DWNT bundle due to the presence of bromine arrangements explains this mechanical instability rather than a charge transfer process. Isotopic 13 C enrichment of the inner tube reduces the frequency of its tangential contribution to the G-band Raman spectrum, which appears to be an effective method to separate the contribution of inner-and outer-tube G + components during pressure evolution. P (onset) c was found to be 12 GPa for the 13 C 60 -derived DWNT system. In this case, the instability of the DWNT is mainly due to the high inhomogeneous filling of the outer tube, as a consequence of the conversion method used to produce the inner-wall nanotube from the peapods, which produces inner tubes which are usually shorter than the outer tubes, leading to the outer tube not being completely filled.
    Physical review. B, Condensed matter 11/2012; 86(19):195410.
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    ABSTRACT: Metallic-impurity-free, nano-sized, short multi-walled carbon nanotubes (MWCNTs) in the form of a tape have been synthesized using stabilized arc discharge under atmospheric conditions. The long, thin tape consisted of crystalline MWCNTs exhibiting indiscernibly blurred interior lattice images and a narrow, hollow core, as well as small and large nanoparticles. The disordered interior regions of the tubes were enlarged into hollow cores by thermal treatment at 2000 °C, suggesting that the elongated tubes crystallize via a super-cooling process. The proposed macroscopic model for the growth process of the tubes in the arc resembles the fiber formation of a recently reported electrospinning process; thermally activated carbon ion and vapor create viscous carbon clusters, and the built-up charge in the clusters leads to the elongation into tubules.
    Carbon. 10/2012; 50(12):4588–4595.
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    ABSTRACT: Through coating with graphene oxides, we have developed a chemical route to the bulk production of long, thin manganese oxide (MnO2) nanowires that have high electrical conductivity. The average diameter of these hybrid nanowires is about 25 nm, and their average length is about 800 nm. The high electrical conductivity of these nanowires (ca. 189.51± 4.51 μS) is ascribed to the homogeneous coating with conductive graphene oxides as well as the presence of non-bonding manganese atoms. The growth mechanism of the nanowires is theoretically supported by the initiation of morphological conversion from graphene oxide to wrapped structures through the formation of covalent bonds between manganese and oxygen atoms at the graphene oxide edge.
    Applied Physics Express 10/2012; 5(10):5001-. · 2.73 Impact Factor
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    ABSTRACT: We report a facile method to efficiently visualize the atomic carbon network of curved few-layered graphitic systems including folded bi-layer graphene, nanoribbon edges and multi-walled carbon nanotubes (straight and bent), via the processing of aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) images. This technique is also able to atomically resolve the structure of overlapping graphene layers with different orientations, thus enabling us to determine the stacking order of multiple graphene layers. To the best of our knowledge, we are the first to identify the stacking order of a misoriented 4-layer closed-edge graphene and a metal-semiconductor double-walled carbon nanotube junction.
    Nanoscale 09/2012; 4(20):6419-24. · 6.23 Impact Factor
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    ABSTRACT: Highly pure double-walled carbon nanotubes (DWCNTs) synthesized by a catalytic chemical vapour deposition method have a well-ordered bundle structure giving explicit diffraction peaks by synchrotron X-ray diffraction measurement. The changes of nanopore structural properties and water adsorptivity of DWCNTs with high-temperature heat treatment were investigated using molecular probe adsorption methods. It was founded that their nanoporosities and apparent hydrophilicities decreased with thermal annealing. However, a specific surface area of 275 m(2) g(-1) and the residual microporosity of more than 60% even after heat treatment at 2673 K suggest their unique applications.
    Nanoscale 07/2012; 4(16):4960-3. · 6.23 Impact Factor
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    ABSTRACT: The introduction of foreign atoms, such as nitrogen, into the hexagonal network of an sp(2)-hybridized carbon atom monolayer has been demonstrated and constitutes an effective tool for tailoring the intrinsic properties of graphene. Here, we report that boron atoms can be efficiently substituted for carbon in graphene. Single-layer graphene substitutionally doped with boron was prepared by the mechanical exfoliation of boron-doped graphite. X-ray photoelectron spectroscopy demonstrated that the amount of substitutional boron in graphite was ~0.22 atom %. Raman spectroscopy demonstrated that the boron atoms were spaced 4.76 nm apart in single-layer graphene. The 7-fold higher intensity of the D-band when compared to the G-band was explained by the elastically scattered photoexcited electrons by boron atoms before emitting a phonon. The frequency of the G-band in single-layer substitutionally boron-doped graphene was unchanged, which could be explained by the p-type boron doping (stiffening) counteracting the tensile strain effect of the larger carbon-boron bond length (softening). Boron-doped graphene appears to be a useful tool for engineering the physical and chemical properties of graphene.
    ACS Nano 06/2012; 6(7):6293-300. · 12.06 Impact Factor
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    ABSTRACT: We report a novel physicochemical route to produce highly crystalline nitrogen-doped graphene nanoribbons. The technique consists of an abrupt N(2) gas expansion within the hollow core of nitrogen-doped multiwalled carbon nanotubes (CN(x)-MWNTs) when exposed to a fast thermal shock. The multiwalled nanotube unzipping mechanism is rationalized using molecular dynamics and density functional theory simulations, which highlight the importance of open-ended nanotubes in promoting the efficient introduction of N(2) molecules by capillary action within tubes and surface defects, thus triggering an efficient and atomically smooth unzipping. The so-produced nanoribbons could be few-layered (from graphene bilayer onward) and could exhibit both crystalline zigzag and armchair edges. In contrast to methods developed previously, our technique presents various advantages: (1) the tubes are not heavily oxidized; (2) the method yields sharp atomic edges within the resulting nanoribbons; (3) the technique could be scaled up for the bulk production of crystalline nanoribbons from available MWNT sources; and (4) this route could eventually be used to unzip other types of carbon nanotubes or intercalated layered materials such as BN, MoS(2), WS(2), etc.
    ACS Nano 03/2012; 6(3):2261-72. · 12.06 Impact Factor
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    ABSTRACT: We present electrical and thermal specific heat measurements that show superconductivity in double-wall carbon nanotube (DWCNT) bundles. Clear evidence, comprising a resistance drop as a function of temperature, magnetoresistance and differential resistance signature of the supercurrent, suggest an intrinsic superconducting transition below 6.8 K for one particular sample. Additional electrical data not only confirm the existence of superconductivity, but also indicate the T(c) distribution that can arise from the diversity in the diameter and chirality of the DWCNTs. A broad superconducting anomaly is observed in the specific heat of a bulk DWCNT sample, which yields a T(c) distribution that correlates well with the range of the distribution obtained from the electrical data. As quasi one dimensionality of the DWCNTs dictates the existence of electronic density of state peaks, confirmation of superconductivity in this material system opens the exciting possibility of tuning the T(c) through the application of a gate voltage.
    Scientific Reports 01/2012; 2:625. · 2.93 Impact Factor

Publication Stats

565 Citations
521.24 Total Impact Points

Institutions

  • 2013–2014
    • Nagaoka University of Technology
      Нагаока, Niigata, Japan
  • 2003–2013
    • Shinshu University
      • • Faculty of Engineering
      • • Institute of Carbon Science and Technology
      Shonai, Nagano, Japan
  • 2012
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Structural Chemistry
      Beijing, Beijing Shi, China
    • Pennsylvania State University
      • Department of Physics
      University Park, MD, United States
  • 2008–2010
    • Massachusetts Institute of Technology
      • • Department of Materials Science and Engineering
      • • Department of Electrical Engineering and Computer Science
      Cambridge, MA, United States
    • Karl-Franzens-Universität Graz
      Gratz, Styria, Austria
  • 2007
    • Universidade Federal do Ceará
      • Departamento de Física
      Fortaleza, Estado do Ceara, Brazil
  • 2006
    • Chiba University
      • Department of Chemistry
      Chiba-shi, Chiba-ken, Japan