Hiroyuki Sugimura

Kyoto University, Kioto, Kyōto, Japan

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Publications (264)632.24 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Surfaces of cyclo-olefin polymers (COPs) are photoactivated by vacuum ultraviolet (VUV) light and can be bonded with a practical bonding strength at low temperatures below Tg. The VUV irradiation condition was optimized, the maximum interfacial toughness was obtained for 5 min of irradiation and a longer irradiation time resulted in a decrease in toughness. We also found that a high-humidity environment caused the decrease in toughness. We investigated the mechanism of the low-temperature bonding of COP by characterizing the fracture surfaces using high-resolution scanning electron microscopy and imaging the bonded interfaces using energy-filtering transmission electron microscopy and scanning transmission electron microscopy. The fracture surfaces exhibited a large number of nanofibrils, whose features are similar to those we previously observed in the polymer–polymer interfaces that were welded in melt conditions. We conclude that the interfacial failure occurs where the polymer chains connected at the interface by hydrogen bonding are pulled out. Thus, the entanglement is important in the bonding of polymers by surface-activation processes.
    No preview · Article · Feb 2016 · Polymer Journal
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    ABSTRACT: Imidazolium-hexafluorophosphate (ImPF6) ionic liquid thin film is prepared on a silicon surface using 3-chloropropyltrimethoxysilane as a bifunctional chemical linker. XPS result revealed the covalent grafting of ImPF6 thin film on a silicon surface. The atomic force microscopic images demonstrated that the ImPF6 thin film is composed of nanoscopic pads/clusters with height of 3–7 nm. Microtribological properties in terms of coefficient of friction and wear-resistivity are probed at the mean Hertzian contact pressure of 0.35–0.6 GPa under the rotational sliding contact. The ImPF6 thin film exhibited low and steady coefficient of friction (μ = 0.11) along with remarkable wear-resistivity to protect the underlying silicon substrate. The low shear strength of ImPF6 thin film, the covalent interaction between ImPF6 ionic liquid thin film and underlying silicon substrate, and its regular grafting collectively reduced the friction and improved the anti-wear property. The covalently grafted ionic liquid thin film further shows immense potential to expand the durability and lifetime of M/NEMS based devices with significant reduction of the friction.
    No preview · Article · Dec 2015 · Applied Surface Science
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    ABSTRACT: Few-layer graphene oxide (GO) is assembled on the silicon surface by a self-assembly approach via covalent interaction using 3-aminopropyltrimethoxysilane (APTMS) as a bifunctional chemical linker. X-ray photoelectron spectroscopy results suggest chemical interactions between oxygen functionalities of GO and amino group of APTMS thin film. The oxygen functionalities of GO thin film are eliminated by vacuum ultraviolet (VUV) photon exposure. Topographic images reveal efficient grafting of GO on the silicon and suggest the presence of few layers in the GO thin film along with wrinkles and folds. Microtribological properties of VUV-reduced GO (rGO) thin film are probed under the mean contact pressure of 0.3-0.6 GPa. The rGO thin film exhibits low and steady friction (0.12-0.15) compared to that of bare silicon (0.6). The rGO thin film could survive for ≈37 000 laps at 100 mN load, revealing its remarkable wear-resistivity. Microscopic images and carbon mapping reveal the deposition of delaminated graphene lamellae on the counter steel ball surface. The low friction and excellent wear-resistivity of rGO thin film are collectively attributed to low-resistance to shear between the neighboring lamellae of rGO, full coverage and strong interaction of rGO thin film with silicon, and deposition of delaminated graphene lamellae on the counter steel surface.
    No preview · Article · Nov 2015 · Advanced Materials Interfaces
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    ABSTRACT: A two-step sharpening process for a Si pillar in a quartz tuning fork sensor was developed for use in frequency modulation atomic force microscopy (FM-AFM). By combining electrochemical etching in HF solution and anisotropic etching in KOH solution, the tip radius was decreased to 120 nm. The Si-probe-attached sensor showed a higher resonance frequency than a tungsten-probe attached sensor, which would lead to a higher force sensitivity. We demonstrated FM-AFM imaging on a cleaved mica surface in aqueous solution by using the fabricated sensor, and atomic resolution was successfully achieved.
    No preview · Article · Sep 2015 · Japanese Journal of Applied Physics
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    ABSTRACT: n-Alkylamines were grafted on basal plane oxygen functionalities of graphene oxide (GO) and synthesized the molecular pillars supported graphene oxide frameworks (GOFs) with tunable interlayer spacing. A major fraction of n-alkylamines was found to covalently interact with basal plane epoxy groups via nucleophilic substitution reaction. The d-spacing in GOFs could be tailored between 10.5 and 28.9 Å by varying the chain length of n-alkylamines. 13C SSNMR explicitly showed the coexistence of both trans and gauche conformation modes. The relative populations of these modes control the conformation heterogeneity and orientation of n-alkylamines in the GOFs. A plausible bilayer structural model of GOFs was demonstrated. The terminal methyl and methylene units of n-alkylamines grafted on GO basal plane were interdigitated with counter layer and afforded double-layer structure of alkyl chains supported GOFs.
    No preview · Article · Jul 2015 · Physical Chemistry Chemical Physics
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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
    No preview · Article · May 2015 · Soft Matter
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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.
    Full-text · Article · Apr 2015 · Chemistry Letters
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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.
    Full-text · Article · Mar 2015 · Applied Physics Letters
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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.
    Full-text · Article · Jan 2015 · ACS Applied Materials & Interfaces
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    ABSTRACT: Hybrid nanomaterials offer task-specific functional properties besides the individual properties of their constituent materials/elements. Herein, graphene–ionic liquid (Gr–IL) hybrid nanomaterials are synthesized to integrate the friction-reducing properties of both ionic liquids and graphene nanosheets. Importantly, the remarkable mechanical strength of graphene improves the anti-wear performance, whereas covalently grafted ionic liquids facilitate the dispersion of the Gr–IL in the polyethylene glycol (PEG 200) synthetic lube base oil. Graphene, prepared by a controlled chemical approach, is used for the covalent grafting of an imidazolium ring. Three variable Gr–IL hybrid nanomaterials, containing bis(salicylato)borate (BScB), oleate (OL), and hexafluorophosphate (PF6) anions, are synthesized to control their surface properties. Detailed chemical and microstructural features of the Gr–IL hybrid nanomaterials are studied using FTIR, XPS, Raman, XRD, FESEM, and HRTEM analyses. The Gr–IL hybrid nanomaterials as lubricant additives for PEG 200 significantly reduced the friction and the wear. Further, the Gr–IL hybrid nanomaterials offer remarkably improved anti-wear properties (55–78%) compared to that of the corresponding ionic liquid (7–39%) blends in PEG 200 and this was attributed to the high mechanical strength of graphene, which protects the contact interfaces against material loss. The elemental and micro-Raman results of the worn surfaces suggested the formation of a tribo-chemical thin film composed of Gr–IL and its tribo-chemical products with steel interfaces. The BScB anion constituted Gr–BScB showed the maximum reduction in friction, whereas the OL analogue exhibited the smallest wear. This study reveals the potential of task-specific Gr–IL hybrid nanomaterials as novel additives for diversified tribological applications.
    No preview · Article · Jan 2015 · Journal of Materials Chemistry A
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    Takashi Ichii · Hiroyuki Sugimura

    Preview · Article · Nov 2014 · Microscopy (Oxford
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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. (Figure Presented).
    Full-text · Article · Oct 2014 · The Journal of Physical Chemistry C
  • Hiroyuki Sugimura · Naruhito Miki · Akihiro Nakamura · Takashi Ichii
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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.
    No preview · Article · Oct 2014 · Chemistry Letters
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    Marvin U. Herrera · Takashi Ichii · Kuniaki Murase · Hiroyuki Sugimura
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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).
    Full-text · Article · Sep 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.
    Full-text · Article · Jul 2014 · Applied Physics Express
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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.
    Full-text · Article · May 2014 · Electrochemistry -Tokyo-
  • Harshal P. Mungse · Om. P. Sharma · Hiroyuki Sugimura · Om P.Khatri
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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.
    No preview · Article · Apr 2014 · RSC Advances
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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).
    No preview · Article · Jan 2014 · Journal of The Surface Finishing Society of Japan

  • No preview · Conference Paper · Oct 2013
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    M. U. Herrera · T. Ichii · K. Murase · H. Sugimura
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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.
    Full-text · Article · Sep 2013 · ECS Transactions

Publication Stats

5k Citations
632.24 Total Impact Points

Institutions

  • 2004-2015
    • Kyoto University
      • Department of Materials Science and Engineering
      Kioto, Kyōto, Japan
  • 1997-2011
    • Nagoya University
      • • Center for Integrated Research in Science and Engineering (CIRSE)
      • • Graduate School of Engineering
      Nagoya, Aichi, Japan
  • 2001
    • Nagoya Municipal Industrial Research Institute
      Nagoya, Aichi, Japan
    • Universitatea Alexandru Ioan Cuza
      • Faculty of Physics
      Socola, Iaşi, Romania
  • 1993
    • Osaka University
      • Department of Applied Physics
      Suika, Ōsaka, Japan