Hiroyuki Sugimura

Kyoto University, Kioto, Kyōto, Japan

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Publications (245)586.75 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces, exhibits excellent mechanical strength, higher thermal stability, and resistance towards oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs) and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil due to van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macro-tribology results showed that the h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and the wear of steel disc. Elemental mapping of worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear are deduced based on experimental results.
    ACS Applied Materials & Interfaces 01/2015; DOI:10.1021/am5083232 · 5.90 Impact Factor
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    ABSTRACT: Molecular-resolution imaging on an alkanethiol self-assembled monolayer (SAM) in an ionic liquid (IL) was demonstrated using frequency modulation atomic force microscopy (FM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, the so-called qPlus sensor, was used as a force sensor. Etch pits, which are a typical structure of alkanethiol SAMs, individual alkanethiol molecules, and single molecular defects were clearly imaged; that is, true molecular-resolution imaging was successfully achieved. We also carried out force curve measurement using the FM-AFM and the presence of a solvation layer on the IL/SAM interface was recognized.
    Chemistry Letters 01/2015; 44(4). DOI:10.1246/cl.141107 · 1.30 Impact Factor
  • Takashi Ichii, Hiroyuki Sugimura
    11/2014; 63 Suppl 1:i10-i11. DOI:10.1093/jmicro/dfu050
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    Takashi Ichii, Masahiro Negami, Hiroyuki Sugimura
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    ABSTRACT: Structural analysis of interfaces between ionic liquid (IL) and alkali-halide (100) surface was demonstrated by frequency modulation atomic force microscopy (FM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip, the so-called qPlus sensor, was used as a force sensor. Atomic-resolution topographic imaging on a KCl(100) surface was successfully achieved in a viscous IL. The square lattice structure with a period of ∼0.4 nm was clearly imaged, which indicated that only K + or Cl − ions were imaged. An abrupt shift of the tip position occurred during the topographic imaging, suggestting that the dissolution of KCl atomic layers was detected by the FM-AFM. In addition, two-dimensional force mapping was carried out, and the presence of the KCl-based layered structure on the interface was recognized. ■ INTRODUCTION Ionic liquids (ILs) are a type of a molten salt usually consisting of organic cations and organic/inorganic anions with melting points below 100 °C or room temperature. Because of their remarkable physical and chemical properties, for example, negligibly low vapor pressure, nonflammability, high ionic conductivity, and high electrochemical stability, they have attracted considerable attention for various applications such as electrochemistry, heterogeneous catalysis, and lubrication. 1 A knowledge of the IL/solid interfacial structure is required to obtain a better understanding of these applications. Frequency modulation atomic force microscopy (FM-AFM) is known to be capable of atomic/molecular-resolution imaging on solid substrates in liquid environments as well as in vacuum and in atmospheric conditions. 2 It can also characterize the density distribution of liquid molecules on liquid/solid interfaces, and the presence of a layered structure on the interface, so-called solvation layers, has been revealed. 3−5 Si cantilevers are usually used as a FM-AFM force sensor. However, the force sensitivity and stability of FM-AFM utilizing Si cantilevers is generally reduced in the case of investigations in viscous liquids such as ILs because the quality factor (Q) of the force sensor is heavily suppressed. To solve this problem, we have used a quartz tuning fork sensor for FM-AFM imaging in ILs instead of a Si cantilever. This sensor showed a much higher Q than a Si cantilever in an IL, typically 100, and atomic-resolution topographic imaging was success-fully achieved. Furthermore, FM-AFM-based force curve measurement, where the frequency shift (Δf) of the force sensor is measured while reducing the tip-to-sample distance along the Z-direction perpendicular to the sample surfaces, enabled us to characterize local solvation structures on IL/solid interfaces. 6 This technique was improved to two-dimensional (2D) force mapping, and the distributions of local solvation structures on IL/solid interfaces was also visualized. 7 Structural analysis on IL/solid interfaces by FM-AFM and its related techniques would provide beneficial information for the IL-based applications mentioned above. In this study, we chose an alkali-halide (AH) (100) surface as the solid sample. AH(100) surfaces have been frequently studied as model insulating samples for atomic-resolution imaging by FM-AFM in an ultrahigh vacuum (UHV) environment because they are typical insulators with chemically inert surfaces and atomically flat surfaces that can be easily obtained just by cleavage. 8,9 FM-AFM imaging on these surfaces in liquid environments is more interesting because it is expected that crystallization and/or dissolution processes can be directly imaged on the atomic scale. In particular, the detailed dissolution mechanism of AH in ILs is still unknown and IL/AH interfaces have not been studied in detail so far. Additionally, structural analysis of IL/AH interfaces by force curve measurements or force mapping would be interesting for the following reasons: It is well-known that an electric double layer is formed on interfaces between metals and electrolytes including ILs. In fact, several AFM studies on IL/metal interfaces including ours indicated the presence of layered structures on the interface. 7,10−14 AH(100) surfaces are electrically neutral because the same numbers of cations and anions are exposed on the surface. Therefore, the structure of an electric double layer on the IL/AH(100) interface is expected to be entirely different from that on IL/metal interfaces, and hence, FM-AFM investigations on IL/ AH(100) interfaces would be significant for understanding the formation mechanism of electric double layers on IL/solid interfaces. Here, we report our structural analysis of IL/AH(100) interfaces by FM-AFM utilizing a quartz tuning fork sensor. Atomic-resolution topographic imaging of an AH(100) surface in an IL was demonstrated. Two-dimensional (2D) force mapping on an IL/AH(100) interface was also carried out. The presence of an electric double layer on the interface and the
    The Journal of Physical Chemistry C 10/2014; 118:26803. DOI:10.1021/jp5078505 · 4.84 Impact Factor
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    ABSTRACT: The creation of a model that explains the dependency of the voltammetric characteristics of ferrocene-terminated Si (Si-Fc) samples on the type of substrate (n- or p-type) would be helpful in understanding the electronic characteristics of these materials. To explain the dependency, Si-Fc samples are treated like diodes. As diodes, the samples may allow charge flow in a certain direction while inhibiting the opposite flow. The treatment of a sample as a diode is done to facilitate analysis of charge flow within the sample, thus enabling easy prediction of its electrochemical characteristics. Likewise, the trend of the anodic peak potential versus light intensity plot (of the samples with n-type substrate) is also associated with the sample’s diode characteristics. Our proposed model opens many scientific possibilities, especially in relating the voltammetric characteristics of electroactive molecules on a Si surface with the properties of a diode (e.g., open-circuit voltage).
    09/2014; 2(1). DOI:10.1002/celc.201402144
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    Yudi Tu, Takashi Ichii, Om Prakash Khatri, Hiroyuki Sugimura
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    ABSTRACT: A dry photoprocess for converting graphene oxide (GO) to reduced GO (rGO) by vacuum–ultraviolet (VUV) irradiation is reported. The rapid reduction of GO was achieved by irradiating a GO sheet in vacuum with 172 nm VUV light at a low power density of 10 mWcm−2. This VUV reduction photochemistry was successfully applied to photolithography by which rGO lines could be drawn on a GO microsheet at a sub-micrometer resolution. This method will be promising for the fabrication of graphene-based microdevices.
    Applied Physics Express 07/2014; 7(7):075101. DOI:10.7567/APEX.7.075101 · 2.57 Impact Factor
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    ABSTRACT: Graphene oxide (GO), an oxidized form of graphene, exhibits immense potential for wide range of applications owing to its rich chemistry. This work reports the controlled deoxygenation of GO under sub- and supercritical hydrothermal conditions, which are considered to be foremost green, environment-friendly and economically viable. The remarkable thermo-physical and chemical properties of water, monitored by temperature (373 - 653 K) and pressure (0.04 - 22.75 MPa), facilitates the deoxygenation of GO. The gradual chemical and structural changes in GO under hydrothermal reactions, over the wide range of temperature and pressure are elucidated on the basis of XPS, FTIR, Raman, XRD, and HRTEM analyses. The plausible deoxygenation mechanism, particularly elimination of hydroxyl, epoxide, carboxyl, and carbonyl groups and repairing of -conjugated network are discussed on the basis of spectroscopic analyses. The addressed hydrothermal route not only avoids the use of toxic and hazardous chemicals as reducing agents but also regulate the deoxygenation events.
    RSC Advances 04/2014; 4(43). DOI:10.1039/c4ra01085j · 3.71 Impact Factor
  • Chemistry Letters 01/2014; 43(10):1557-1559. DOI:10.1246/cl.140594 · 1.30 Impact Factor
  • 224th ECS Meeting; 10/2013
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    ABSTRACT: Vinylferrocene-terminated Si(111) was prepared by illuminating visible light onto a hydrogen-terminated Si(111) surface that was immersed in either diethyl ether-vinylferrocene or dibutyl ether-vinylferrocene solution. The use of either diethyl ether or dibutyl ether as grafting medium yielded a neutral ferrocenyl monolayer that was electrically connected with the silicon substrate. Both preparation media produce samples that have good electrochemical characteristics e. g., low peak potential separation and linear plot of peak current density with scan rate. The use of dibutyl ether as grafting solution resulted to a fast grafting rate, in which the optimum grafting time for samples with n-type and p-type substrates were 0.5 h and 1 h, respectively. Meanwhile, the use of diethyl ether resulted to the presence of lumps of deposited materials on the grafted surface. Nevertheless, even if these materials may be considered as impurities, these did not distort significantly the electrochemical characteristics of the sample.
    ECS Transactions 09/2013; 50(54):37-46. DOI:10.1149/05054.0037ecst
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    ABSTRACT: Fluorescence microscopy is used extensively in cell-biological and biomedical research, but it is often plagued by three major problems with the presently available fluorescent probes: photobleaching, blinking, and large size. We have addressed these problems, with special attention to single-molecule imaging, by developing biocompatible, red-emitting silicon nanocrystals (SiNCs) with a 4.1-nm hydrodynamic diameter. Methods for producing SiNCs by simple chemical etching, for hydrophilically coating them, and for conjugating them to biomolecules precisely at a 1:1 ratio have been developed. Single SiNCs neither blinked nor photobleached during a 300-min overall period observed at video rate. Single receptor molecules in the plasma membrane of living cells (using transferrin receptor) were imaged for ≥10 times longer than with other probes, making it possible for the first time to observe the internalization process of receptor molecules at the single-molecule level. Spatial variations of molecular diffusivity in the scale of 1-2 µm, i.e., a higher level of domain mosaicism in the plasma membrane, were revealed.
    The Journal of Cell Biology 09/2013; 202(6):967-83. DOI:10.1083/jcb.201301053 · 9.69 Impact Factor
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    ABSTRACT: The photochemical grafting of methyl groups onto an n-type Si(111) substrate was successfully achieved using a Grignard reagent. The preparation involved illuminating a hydrogen-terminated Si(111) that was immersed in a CH3MgBr-THF solution. The success was attributed to the ability of the n-type hydrogenated substrate to produce holes on its surface when illuminated. The rate of grafting methyl groups onto the silicon surface was higher when a larger illumination intensity or when a substrate with lower dopant concentration was used. In addition, the methylated layer has an atomically flat structure, has a hydrophobic surface, and has electron affinity that was lower than the bulk Si.
    Journal of Colloid and Interface Science 08/2013; 411. DOI:10.1016/j.jcis.2013.08.035 · 3.55 Impact Factor
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    ABSTRACT: Anodic dissolution of elemental Mg was examined in an ionic liquid, trimethyl-n-hexylammonium bis[(trifluoromethyl)-sulfonyl]amide (TMHA-Tf2N), containing a simple salt, Mg(Tf2N)(2), having a common anion. faradaic anodic dissolution was markedly stimulated in the presence of water dissolved within its solubility limit. The dissolution current efficiency for elemental Mg was found to be almost 100% without decreasing the water content, indicating that spontaneous reaction of Mg with water was limited and water molecules play a catalytic role in the overall dissolution mechanism, where a magnesium(1) oxide/hydroxide is involved. The Mg2+/Mg-0 redox potentials, or onset potentials for Mg dissolution, vs. Li+/Li-0 redox with and without water were also estimated from a set of sampled-current voltammograms obtained by a potential-step method.
    Journal of The Electrochemical Society 07/2013; 160(10):D453-D458. DOI:10.1149/2.057310jes · 2.86 Impact Factor
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    ABSTRACT: Single-phase Cu–Sn intermetallics were used to investigate their phase transformations during lithiation/delithiation, together with their negative-electrode properties. The stoichiometric Cu–Sn samples were prepared as thermodynamically warranted phases using a reduction-diffusion method with controlled potentials. Potentiostatic lithiation tests suggested that Cu3Sn directly changes into LixSn, while Cu6Sn5 becomes Li2CuSn before LixSn forms. We also revealed that separation from Li2CuSn into Cu and LixSn occurs at +0.11 to +0.10 V vs. Li. Additionally, charging/discharging tests with cutoff potentials of +1.5 V to +0.11 V showed better cycling performance than that with +1.5 V to +0.00 V, probably due to the suppression of LixSn formation. Such a tendency can be expected in other Cu6Sn5 electrode materials.
    Electrochimica Acta 05/2013; 98:239–243. DOI:10.1016/j.electacta.2013.03.035 · 4.09 Impact Factor
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    S. Mo, T. Ichii, K. Murase, H. Sugimura
    ECS Transactions 03/2013; 50(6):137-143. DOI:10.1149/05006.0137ecst
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    ABSTRACT: A new integration technique of Deoxyribonucleic acid (DNA) origami as an excellent platform to arrange various nanomaterials such as metallic nanoparticles, carbon nanotubes and proteins and so on with nanometer scale resolution into MEMS utilizing DNA hybridization of a complementary pair of single-strand DNAs (ssDNAs) was demonstrated. A contact-mode atomic force microscopy (AFM) based lithography was adopted to form ssDNA modified patterns into an organic thin film with 30 nm resolution on a silicon substrate. A newly designed DNA origami (30 nm × 150 nm) with ssDNA as sticky ends was successfully fixed at specific positions of the substrate by DNA hybridization.
    Micro Electro Mechanical Systems (MEMS), 2013 IEEE 26th International Conference on; 01/2013
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    ABSTRACT: It is essential to immobilize gold nanoparticles (AuNPs) firmly onto a certain substrate in a closely packed manner to apply plasmonic functions of AuNP in photonic/electronic devices. AuNP-Si systems are of particular interest for the integration of plasmonics to semiconductor electronics. Here we report on the arrangement of AuNPs into a 2-D array that was covalently bonded to a Si substrate without surface oxide. This process was achieved by simply irradiating visible light to a hydogen-terminated Si substrate immersed in a solution of AuNPs covered with a self-assembled monolayer (SAM) of 11-mercaptoundecene (MUD). These MUD-AuNPs were attached to the substrate by forming Si–C bonds as a result of the photochemical reaction between Si–H groups on the substrate and vinyl groups of the MUD-SAMs. The reaction proceeded most effectively at a wavelength band around 520 nm adjusted to the plasmonic resonance peak of the MUD-AuNPs(20 nm in diameter)/toluene solution centered at 535 nm, demonstrating that the photochemical reaction was assisted by localized surface plasmon, which allowed the AuNPs to be photon collectors.
    The Journal of Physical Chemistry C 09/2012; 117(6):2480–2485. DOI:10.1021/jp306290w · 4.84 Impact Factor
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    ABSTRACT: Frequency modulation atomic force microscopy (FM-AFM) imaging in ionic liquids (ILs) were carried out. A quartz tuning fork sensor with a sharpened tungsten tip was used as a force sensor instead of a Si cantilever. Only the tip apex was immersed in ILs and the quality factor of the sensors was kept more than 100 in spite of the high viscosity of ILs. Atomic-resolution topographic imaging was successfully achieved in an IL as well as in an aqueous solution. In addition, frequency shift versus tip-to-sample distance curves were obtained and the structures of local solvation layers were studied.
    Japanese Journal of Applied Physics 08/2012; 51(8). DOI:10.1143/JJAP.51.08KB08 · 1.06 Impact Factor
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    ABSTRACT: UV photon induced assembly of ω-alkenyl terminated gold nanoparticles (AuNPs) on pre-defined sites of crystalline silicon surface through covalent interaction is demonstrated. Highly ordered and stable hexadecyl monolayer on oxide free silicon surface is used to construct the photopattern and then the linear patterns of hydrogen-terminated sites were effectively used to assemble AuNPs by UV induced hydrosilylation. This approach is entirely based on oxide free interfaces, where both robust organic monolayer and AuNPs are assembled in a linear fashion. The developed strategy promises immense potential to miniaturize silicon based devices for technological applications, where electron coupling between the nanoparticles and the silicon surface is very significant. This work further paving the new direction to immobilize various types of nanoparticles in different architecture on oxide free crystalline silicon surface to exploit their utilization in technological applications.
    Journal of Materials Chemistry 07/2012; 22(32):16546-16551. DOI:10.1039/C2JM32875E · 6.63 Impact Factor
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    ABSTRACT: Synthesis of ω-alkenyl-terminated silver nanoparticles (AgNPs) and then their immobilization on a hydrogen-terminated silicon surface in two-dimensional arrangement through covalent interaction are demonstrated. The thermal-induced hydrosilylation at mild conditions facilitate nanoparticles assembly through interaction between terminal alkenyl (CH(2)=CH-) groups of AgNPs and hydrogen-terminated silicon surface. The assembly of AgNPs on a silicon surface is characterized by FESEM and XPS. Adequate coating of 10-undecene-1-thiol (UDT) on AgNPs and mild temperature hydrosilylation impede the fusion or aggregation of nanoparticles, while they immobilized on a silicon surface, which is very crucial to preserve the discrete entities of nanoparticles. This elegant and facile approach provides stable monolayer of AgNPs with very good coverage area and promises potential to fabricate electronic devices and solar cells, where nanoparticles needs to be directly attached to the silicon surface without an interfacial oxide thin film.
    Journal of Colloid and Interface Science 06/2012; 382(1):22-7. DOI:10.1016/j.jcis.2012.06.001 · 3.55 Impact Factor

Publication Stats

3k Citations
586.75 Total Impact Points


  • 2004–2014
    • Kyoto University
      • Department of Materials Science and Engineering
      Kioto, Kyōto, Japan
    • Kanagawa Academy of Science and Technology
      Kawasaki Si, Kanagawa, Japan
  • 1998–2006
    • Nagoya University
      • • Center for Integrated Research in Science and Engineering (CIRSE)
      • • Graduate School of Engineering
      Nagoya-shi, Aichi-ken, Japan
  • 2003
    • Nippon Paint Co., Ltd.
      Ōsaka, Ōsaka, Japan
    • RMD Research and Development Center
      Bulsār, Gujarat, India
  • 2002–2003
    • Chubu University
      Касугай, Aichi, Japan
  • 2000–2001
    • Universitatea Alexandru Ioan Cuza
      • Faculty of Physics
      Socola, Iaşi, Romania
  • 1999
    • Chiba Institute of Technology
      Tiba, Chiba, Japan
  • 1992–1994
    • Osaka University
      • Department of Applied Physics
      Suika, Ōsaka, Japan
  • 1993
    • Tohoku University
      • Division of Aging Science
      Miyagi, Japan