Hiroyuki Sugimura

Kyoto University, Kioto, Kyōto, Japan

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Publications (228)547.72 Total impact

  • Takashi Ichii, Hiroyuki Sugimura
    Microscopy (Oxford, England). 11/2014; 63 Suppl 1:i10-i11.
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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. · 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).
    ChemElectroChem. 09/2014;
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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. · 2.73 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; · 3.71 Impact Factor
  • 224th ECS Meeting; 10/2013
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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; · 3.55 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. · 4.09 Impact Factor
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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. · 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). · 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. · 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. · 3.55 Impact Factor
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    ABSTRACT: We have fabricated gold nanoparticle (AuNP) arrays on indium-tin oxide (ITO) substrates in a nearly one-dimensional fashion. AuNPs were site-selectively immobilized on ITO of which the surface had been patterned by a nanolithography process based on scanning probe microscopy. The fabricated nanoscale lines covered with aminosilane self-assembled monolayer served as chemisorption sites for citrate-stabilized AuNPs of 20 nm in diameter, accordingly, AuNP nanolines with a thickness of single nanoparticle diameter were spontaneously assembled on the lines. In this 1D array, the AuNPs were almost separated from each other due to the electrostatic repulsion between their negatively charged surface layers. Furthermore, a reorganization process of the immobilized AuNP arrays has been successfully demonstrated by replacing each AuNP's surface layer from citric acid to dodecanethiol. By this process, the AuNPs lost their electrostatic repulsion and became hydrophobic so as to be attracted to each other through hydrophobic interaction, resulting in reorganization of the AuNP array. By repeating the deposition and reorganization cycle, AuNPs were more densely packed. The optical absorption peak of the arrays due to their plasmonic resonance was found to shift from 526 to 590 nm in wavelength with repeating cycles, indicating that the resonance manner was changed from the single nanoparticle mode to the multiple particle mode with interparticle coupling.
    Langmuir 05/2012; 28(20):7579-84. · 4.38 Impact Factor
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    ABSTRACT: Highly controlled arrays of gold nanoparticles (AuNPs) were fabricated on optically transparent indium tin oxide (ITO) substrates by combining atomic force microscope (AFM) lithography and surface modification using self-assembled monolayers (SAMs). The nanopatterns of methyl and amino groups were fabricated on ITO substrates and AuNPs were assembled just on the amino-terminated nanopatterns, which is based on the different affinities of the AuNPs for the functional groups. The site selectivity was intensively improved by dehydration and repairing defects in a long alkylsilane SAM with short alkylsilane molecules.
    Applied Physics Express 02/2012; 5(2):5202-. · 2.73 Impact Factor
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    ABSTRACT: Gold (Au) nanostructures have been fabricated on various substrates, such as Si, ITO and quartz glass, through the position-selective deposition of Au nanoparticles. This self-aligned deposition of the nanoparticles is promoted through the electrostatic interaction between the nanoparticles and the deposition sites, which are charged negatively and positively, respectively. Prior to the nanoparticle deposition, the positively charged sites where covered with aminosilane self-assembled monolayer had been constructed on the substrate with an artificial pattern design by a lithographic method. A photolithographic process, which was based on direct photochemical modification of organic substances induced by irradiating with a vacuum ultra-violet (VUV) light, was employed so that sub-μm features down to 500 nm have been successfully fabricated and provided as templates for aligning Au nanoparticles. The second method for patterning was electrochemical line drawing using a scanning probe microscope. One-dimensional arrays of Au nanoparticles with a line thickness of a single nanoparticle diameter have been successfully fabricated. In addition, by replacing a surface charged layer consisting of citric acid molecules surrounding the Au nanoparticles with alkanethiol molecules, the Au nanoparticles were neutralized so that the fabricated Au nanoparticle array in which most of the nanoparticles were separated each other was re-organized to a more closely packed structure.
    Procedia Engineering 01/2012; 36:374–381.
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    ABSTRACT: The molecular density of an aminosilane self-assembled monolayer formed from N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPS) by a vapor phase method has been estimated to be about 3 AEAPS molecules per nm(2) based on chemical labeling, optical absorption spectroscopy and X-ray photoelectron spectroscopy.
    Chemical Communications 08/2011; 47(31):8841-3. · 6.38 Impact Factor
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    ABSTRACT: Electrochemically active self-assembled monolayers (SAM) have been successfully fabricated with atomic-scale uniformity on a silicon (Si)(111) surface by immobilizing vinylferrocene (VFC) molecules through Si-C covalent bonds. The reaction of VFC with the hydrogen-terminated Si (H-Si)(111) surface was photochemically promoted by irradiation of visible light on a H-Si(111) substrate immersed in n-decane solution of VFC. We found that aggregation and polymerization of VFC was avoided when n-decane was used as a solvent. Voltammetric quantification revealed that the surface density of ferrocenyl groups was 1.4×10(-10) mol cm(-2), i.e., 11% in substitution rate of Si-H bond. VFC-SAMs were then formed by the optimized preparation method on n-type and p-type Si wafers. VFC-SAM on n-type Si showed positive photo-responsivity, while VFC-SAM on p-type Si showed negative photo-responsivity.
    Journal of Colloid and Interface Science 06/2011; 361(1):259-69. · 3.55 Impact Factor
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    ABSTRACT: Nanostructures consisting of concentric Au circles with a nm-scale line thickness have been fabricated on silicon (Si) substrates based on electroless plating and by the use of scanning probe microscope as a lithographic tool. First, a micro-template was fabricated on a hexadecyl self-assembled monolayer (HD-SAM) covalently bonded to a Si(111) substrate by scanning probe anodization lithography in which the HD-SAM was locally degraded and the substrate Si was anodized along a trace of an conductive AFM-tip biased negatively to the grounded Si substrate. Anodic Si oxide formed by this local anodization process was then etched with HF in order to expose the Si surface under the anodic oxide layer. Consequently, a Si nanopattern surrounded with the HD-SAM identical to the anodic oxide pattern was formed. This Si nanopattern served as a template for fabricating a Au nanostructure by means of electroless plating. Due to the galvanic displacement of surface Si atoms with Au complex ions in a plating bath, Au started to nucleate on the exposed Si surface, while no nuclei was formed on the surrounding HD-SAM. Consequently, a Au nanostructure was formed through further Au deposition on the Au nuclei. The fabricated Au nanostructures are promising for applications emerging plasmonic functions.
    Journal of Photochemistry and Photobiology A Chemistry 06/2011; 221(2):209-213. · 2.29 Impact Factor
  • Kuniaki Murase, Akira Ito, Takashi Ichii, Hiroyuki Sugimura
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    ABSTRACT: A novel metallization of non-conductive epoxy substrate with Cu-Sn “speculum alloy,” or “white bronze,” was performed through successive electrochemical processes: (i) conventional electroless deposition of pure Cu layer and (ii) subsequent electrochemical alloying of the resulting pure Cu layer with Sn using an ionic liquid bath at 150°C, a medium-low temperature. Availability of the Sn quasi-reference electrode for the alloying was verified, and the resulting compact and adhesive Cu-Sn layers, composed of Cu6Sn5 and/or Cu3Sn intermetallic phases, were examined as an alternative to nickel plating. The abundance of the two intermetallic phases was found to be dependent on the alloying potential and duration, and was discussed in terms of alloy formation thermodynamics of the Cu-Sn system.
    Journal of The Electrochemical Society. 05/2011; 158(6):D335-D341.

Publication Stats

2k Citations
547.72 Total Impact Points

Institutions

  • 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
  • 1993
    • Tohoku University
      Japan