Hiroyuki Sugimura

Kyoto University, Kioto, Kyōto, Japan

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Publications (254)597.75 Total impact

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    ABSTRACT: Vacuum ultraviolet (VUV, λ = 172 nm) irradiation of alkyl self-assembled monolayers (SAMs) in the presence of dry air alters their surface properties. In this work, UV photochemically prepared hexadecyl (HD)-SAMs on hydrogen-terminated silicon substrates were irradiated by the VUV light in dry air, which generates active oxygen species by excitation of the atmospheric oxygen molecules. These active oxygen species convert the terminal methyl groups of the SAMs to polar functional groups, which were examined quantitatively by X-ray photoelectron spectroscopy (XPS) and chemical labeling. At the first stage of the VUV irradiation, the SAMs’ surface was functionalized, and the ratios of the generated polar functional groups markedly increased. With elongation of the irradiation period, the SAMs were gradually degraded, and the total polar group percentages gradually decreased. The difference between the oxygenated carbon components derived by the deconvolution of the XPS carbon (C1s) spectrum and the chemical labeling of polar groups revealed enormous quantities of ethereal and ester groups that cannot react with the labeling agents but are included in the C1s spectral envelope. These modifications were reflected on the SAMs’ morphological structures, which were gradually distorted until a complete amorphous structure was obtained after the complete elimination of HD-SAMs
    Soft Matter 05/2015; DOI:10.1039/C5SM00823A · 4.15 Impact Factor
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    Yudi Tu, Takashi Ichii, Toru Utsunomiya, Hiroyuki Sugimura
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    ABSTRACT: We here report a scanning probe method to locally and directly research the electrical properties of vacuum-ultraviolet (VUV) reduced graphene oxide. The measured electrical conductivity of individual VUV-reduced GO (VUV-rGO) sheets by using conductive atomic force microscopy (CAFM) reached 0.20 S·m−1 after 64 min irradiation, which was clearly enhanced compared with the pristine GO. According to the X-ray photoelectron spectroscopy results, the recovered conductivity of VUV-rGO could be ascribed to the partial elimination of oxygen-containing functional groups and the rapid reconstruction of the C=C bonds. Heterogeneously distributed low- and high-conductivity domains (with a diameter of tens of nanometer to ca. 500 nm) were found from current mapping of the VUV-rGO sheet. By applying photomask lithography, rGO regions were drawn into single GO sheet and were researched by CAFM. The in-plane lateral conductivity of rGO regions increased obviously compared with pristine GO regions.
    Applied Physics Letters 03/2015; 106(13):133105. DOI:10.1063/1.4916813 · 3.52 Impact Factor
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    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; 7(6). 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 ability to reduce palladium (Pd) ions to Pd nanoparticles has been provided on the surface of cycloolefin polymer (COP). The origin of this reductive function is aldehyde and alcoholic hydroxy groups formed by oxidizing the COP surface with active oxygen species, which were generated through the irradiation of atmospheric oxygen and water molecules with vacuum ultraviolet light of 172 nm in wavelength. The Pd nanoparticles successfully served as catalysts for electroless plating.
    Chemistry Letters 10/2014; 43(10):1557-1559. DOI:10.1246/cl.140594 · 1.30 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: Structural analysis of the interfaces between an ionic liquid (IL) and an organic monolayer was carried out by phase modulation atomic force microscopy (PM-AFM). A quartz tuning fork sensor with a sharpened tungsten tip was used as a force sensor instead of a Si cantilever. Topographic imaging of the monolayer-covered Si(111) substrate revealed that the PM-AFM is capable of imaging the atomic steps originating from the substrate in an IL. We also carried out force curve measurement using the PM-AFM in order to directly confirm the presence of solvation layers and revealed that at least 4 layers, each with a thickness of 0.77 nm, were formed on the interface. In addition, we obtained topographic images at different driving frequencies and indicated that it is possible to image not only the sample surface but also the solvation layers formed on the IL/monolayer interface.
    Electrochemistry -Tokyo- 05/2014; 82(5):380-384. DOI:10.5796/electrochemistry.82.380 · 0.98 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
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    ABSTRACT: For application to synthetic resin parts and to the fabrication of microfluidic devices made of cyclo-olefin polymer (COP), an adhesiveless bonding technology was developed: photo-activation bonding. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for COP surface modification. The surface modification procedure is extremely simple. A COP plate placed in air with atmospheric pressure is irradiated with the VUV light. Based on VUV photochemistry assisted with atmospheric oxygen, a modified layer including large amounts of polar functional groups (-OH, -CHO, -COOH, etc.) is formed on the COP plate. The VUV-modified COP plates were bonded at a low temperature through attractive interactions between the modified layers on the COP plates without deforming the plates' preformed microstructures. A strength test of bonding was conducted to elucidate the effects of surface modification and bonding conditions such as VUV-irradiation distance (dVUV), VUV-irradiation time (tVUV), bonding pressure (PB), bonding temperature (TB), and bonding time (tB).
    Journal of The Surface Finishing Society of Japan 01/2014; 65(5):234-239. DOI:10.4139/sfj.65.234
  • 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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    Shihang Mo, Takashi Ichii, Kuniaki Murase, Hiroyuki Sugimura
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    ABSTRACT: Closely packed two-dimensional (2D) arrays of gold nanoparticles (AuNPs) were successfully immobilized on Si(111) substrates, using the photochemical reaction between alkanethiol-capped AuNPs and hydrogen-terminated silicon surfaces (Si-H). This process provides a new approach to construct high-density AuNP nanostructures on a semiconductor substrate. Optical property measurements demonstrated that the plasmonic properties of the AuNP arrays can be tuned by controlling the density and the interparticle distance of the AuNPs.
    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

Publication Stats

4k Citations
597.75 Total Impact Points

Institutions

  • 2004–2015
    • 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
  • 2001
    • Nagoya Municipal Industrial Research Institute
      Nagoya, 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