Kenji Kawaguchi

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

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Publications (72)166.79 Total impact

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    ABSTRACT: In this paper, we have further developed our simple (one-pot) and rapid (short irradiation time) laser fabrication process of submicrometer spheres composed of amorphous calcium iron phosphate. In our previous process, laser irradiation was applied to a calcium phosphate (CaP) reaction mixture supplemented with ferric ions (Fe(3+)) as a light-absorbing agent. Because the intention of the present study was to fabricate magnetite-encapsulated CaP-based submicrometer spheres, ferrous ions (Fe(2+)) were used as a light-absorbing agent rather than ferric ions. The ferrous ions served as a light-absorbing agent and facilitated the fabrication of submicrometer and micrometer spheres of amorphous calcium iron phosphate. The sphere formation and growth were better promoted by the use of ferrous ions as compared with the use of ferric ions. The chemical composition of the spheres was controllable through adjustment of the experimental conditions. By the addition of sodium hydroxide to the CaP reaction mixture supplemented with ferrous ions, fabrication of CaP-based magnetic submicrometer spheres was successfully achieved. Numerous magnetite and wüstite nanoparticles were coprecipitated or segregated into the CaP-based spherical amorphous matrix via light-material interaction during the CaP precipitation process. The magnetic properties of the magnetite and wüstite formed in the CaP-based spheres were investigated by magnetization measurements. The present process and the resulting CaP-based spheres are expected to have great potential for biomedical applications.
    Physical Chemistry Chemical Physics 03/2015; 17(14). DOI:10.1039/c4cp05740f · 4.20 Impact Factor
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    ABSTRACT: Biomimetic calcium phosphate (CaP) precipitation processes using supersaturated CaP solutions are useful in surface functionalization of biomedical materials. We applied our laser-assisted biomimetic (LAB) process to successfully achieve rapid single-step CaP precipitation on the surface of titanium metal, which is an important metallic biomaterial, by applying pulsed laser irradiation to the titanium substrate immersed in a supersaturated CaP solution. Precipitation occurred via the combined effect of laser surface modification and ambient heating. Moreover, we demonstrated immobilization of various contents of osteogenic substances (zinc and fibronectin components) on the titanium surface together with CaP by supplementing the CaP solution with these substances. The LAB process is expected to be a facile and effective surface functionalization technique for titanium-based biomaterials to provide them with osteoconductivity because of CaP and stimulatory effects on bone formation due to osteogenic substances.
    Colloids and Interface Science Communications 01/2015; 4. DOI:10.1016/j.colcom.2015.03.003
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    ABSTRACT: Calcium phosphate deposition was induced on optically semitransparent polymers, but not on a transparent polymer, by a pulsed laser irradiation process in a supersaturated solution. This process would be useful as a tool for depositing calcium phosphate on laser-absorbing polymers.
    RSC Advances 10/2014; 4(96). DOI:10.1039/C4RA09313E · 3.84 Impact Factor
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    ABSTRACT: We developed a simple and quick physicochemical process for fabricating calcium iron phosphate submicrometre spheres. Here, pulsed laser irradiation was performed to a calcium phosphate reaction mixture supplemented with ferric ions as a light-absorbing agent. The size and chemical composition of the spheres were controllable through the experimental conditions.
    RSC Advances 08/2014; 4(72). DOI:10.1039/C4RA04941A · 3.84 Impact Factor
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    ABSTRACT: A bottom-up based photomediated strategy is presented to create single crystalline silver spherical particles by pulsed laser irradiation of silver nanoparticles in liquid, where the unique selective laser heating is responsible for the formation of spherical particles. The present approach is facile and flexible for the design of silver spherical particles with tunable sizes. Systematical studies reveal that the experimental parameters including laser fluence, laser irradiation time, dispersing liquid, and concentration of starting material are important factors that influence the formation of silver spherical particles. As a demonstration of the as-synthesized silver spheres for electrochemical applications, the performance of silver spherical particles as potential supercapacitors was investigated by cyclic voltammetry, and the results indicated a higher capacity of silver spherical particles compared to that of silver raw nanoparticles, which is considered to originate from the enhanced electronic conductivity due to the single crystalline feature of silver spherical particles. We believe that the photomediated method presented in this work can be set as a new alternative in creating a variety of noble metallic spherical particles.
    12/2012; 1(3):692-698. DOI:10.1039/C2TA00389A
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    ABSTRACT: A new one-step approach was developed to synthesize bimetallic alloy submicrometer spheres, which are immiscible under equilibrium, using AuCo as a model system. Uniform, single-phase AuCo alloy submicrometer particles (230 nm) with a well-defined spherical morphology were successfully formed via pulsed laser irradiation of Au and Co-oxides nanoparticles dispersed in ethanol and characterized with a combination of electron microscopy, diffraction and magnetization measurements.
    RSC Advances 11/2012; 3(1):79-83. DOI:10.1039/C2RA22119E · 3.84 Impact Factor
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    ABSTRACT: The present authors recently developed a new calcium phosphate (CaP) coating technique on an ethylene-vinyl alcohol copolymer substrate utilizing a laser-assisted biomimetic (LAB) process. In the present study, the LAB process was applied to a sintered hydroxyapatite (sHA) substrate for CaP coating. The LAB process was carried out by irradiating the sHA substrate immersed in a supersaturated CaP solution with a low-energy Nd-YAG pulsed laser. Within 30 min of irradiation, contiuous CaP layers with different morphologies were successfully formed on the laser-irradiated sHA surface. A submicron cavernous structure of the CaP layer was developed into a micron flake-like structure as the laser power increased from 1 to 3 W. This result suggests that the secondary nucleation and growth of CaP crystals were accelerated by laser irradiation in a power-dependent manner. Laser absorption by the sHA substrate and the resulting increase in ambient temperature locally near the surface should be responsible for the accelerated CaP nucleation and growth. The present CaP coating technique using the LAB process is simple and quick, hence it would be useful in orthopedic and dental applications as an on-demand surface-functionalization method for biomaterials consisting of sHA.
    Key Engineering Materials 11/2012; 529-530(1):217-222. DOI:10.4028/www.scientific.net/KEM.529-530.217 · 0.19 Impact Factor
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    ABSTRACT: Simple, mild, and area-specific calcium phosphate (CaP) coating techniques are useful for the production and surface modification of biomaterials. In this study, an area-specific CaP coating technique for polymer substrates was successfully developed using a liquid-phase laser process. In the proposed method, Nd-YAG laser light (355 nm, 30 Hz, and 1-3 W) irradiated an ethylene-vinyl alcohol copolymer (EVOH) substrate immersed in a supersaturated CaP solution for various periods of time (up to 30 min). The CaP-forming ability increased with an increase in the laser power and irradiation period. At the optimal laser power (3 W), a continuous CaP layer formed within 30 min on the laser-irradiated surface of the EVOH substrate. The formation of CaP was attributed to laser absorption by the EVOH substrate, which promoted the surface modification of EVOH and an increase in the temperature of the solution near the surface of the substrate. The resulting CaP coating showed better cell adhesion property than the naked EVOH substrate. The proposed CaP coating technique is simple (quick and single step) and area specific. Furthermore, the present process is carried out under mild conditions, that is, at normal pressures and temperatures in a safe aqueous medium. These are significant advantages of the proposed CaP coating technique.
    Journal of Biomedical Materials Research Part A 10/2012; 100(10):2573-80. DOI:10.1002/jbm.a.34192 · 3.37 Impact Factor
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    ABSTRACT: We report the synthesis of Au-based submicrometer-sized spherical particles with uniform morphology/size and integrated porosity-magnetic property in a single particles. The particles are synthesized by a two-step process: (a) selective pulsed laser heating of colloidal nanoparticles to form particles with Au-rich core and Fe-rich shell and (b) acid treatment which leads to formation of porous architecture on particle surface. The simple, fast, inexpensive technique that is proposed demonstrates very promising perspectives for synthesis of composite particles.
    Langmuir 03/2012; 28(11):4903-7. DOI:10.1021/la2038334 · 4.46 Impact Factor
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    ABSTRACT: The development of a general method to fabricate spherical semiconductor and metal particles advances their promising electrical, optical, magnetic, plasmonic, thermoelectric, and optoelectric applications. Herein, by using CuO as an example, we systematically demonstrate a general bottom-up laser processing technique for the synthesis of submicrometer semiconductor and metal colloidal spheres, in which the unique selective pulsed heating assures the formation of spherical particles. Importantly, we can easily control the size and phase of resultant colloidal spheres by simply tuning the input laser fluence. The heating-melting-fusion mechanism is proposed to be responsible for the size evolution of the spherical particles. We have systematically investigated the influence of experimental parameters, including laser fluence, laser wavelength, laser irradiation time, dispersing liquid, and starting material concentration on the formation of colloidal spheres. We believe that this facile laser irradiation approach represents a major step not only for the fabrication of colloidal spheres but also in the practical application of laser processing for micro- and nanomaterial synthesis.
    Chemistry - A European Journal 01/2012; 18(1):163-9. DOI:10.1002/chem.201102079 · 5.70 Impact Factor
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    ABSTRACT: Size-tailored ZnO submicrometer spheres are synthesized based on bottom-up laser processing. A heating-melting-evaporating mechanism is responsible for the formation of submicrometer-scale spherical particles. The size-related optical extinction and selective aniline trapping on ZnO submicrometer spheres indicate that they are potential candidates for optical and gas-sensing applications.
    Advanced Materials 04/2011; 23(16):1865-70. DOI:10.1002/adma.201100078 · 17.49 Impact Factor
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    ABSTRACT: Spherical iron oxide nanocomposite particles composed of magnetite and wustite have been successfully synthesized using a novel method of pulsed laser irradiation in ethyl acetate. Both the size and the composition of nanocomposite particles are controlled by laser irradiation condition. Through tuning the laser fluence, the Fe3O4/FeO phase ratio can be precisely controlled, and the magnetic properties of final products can also be regulated. This work presents a successful example of the fabrication of ferro (ferri) (FM)/antiferromagnetic (AFM) systems with high chemical stability. The results show this novel simple method as widely extendable to various FM/AFM nanocomposite systems.
    Nanoscale Research Letters 03/2011; 6(1):226. DOI:10.1186/1556-276X-6-226 · 2.48 Impact Factor
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    ABSTRACT: A simple approach to prepare carbon quantum dots is presented in this communication by laser rapid passivation of nano carbon particles in ordinary organic solvent. The as-prepared carbon dots exhibited visible, tunable and stable photoluminescence (PL). XPS analysis showed that the increased oxygen concentration might be concerned with the origin of PL.
    Chemical Communications 11/2010; 47(3):932-4. DOI:10.1039/c0cc03552a · 6.83 Impact Factor
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    ABSTRACT: Canned heat: Inhibition of anisotropic crystal growth is critical for synthesizing semiconductor/metal spheres, but it is kinetically difficult to achieve in methods relying on conventional heating. Selective heating of colloidal nanoparticles by pulsed laser irradiation allows size-tailored semiconductor and metal submicrometer spheres to be synthesized.
    Angewandte Chemie International Edition 08/2010; 49(36):6361-4. DOI:10.1002/anie.201002963 · 11.26 Impact Factor
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    Angewandte Chemie 08/2010; 122(36):6505 - 6508. DOI:10.1002/ange.201002963
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    ABSTRACT: Electronic structure of individual boron nanobelts, which supposedly have α-tetragonal boron structure, was studied with electron energy-loss spectroscopy (EELS) and soft X-ray emission spectroscopy (SXES) in a transmission electron microscope. A boron K-shell excitation spectrum by EELS and boron K-emission spectra by SXES correspond to partial density of states of the conduction and the valence bands, respectively. Experimental results reveal that boron nanobelts are either a semimetal or narrow-gap semiconductor.
    Journal of Physics Conference Series 07/2009; 176(1):012029. DOI:10.1088/1742-6596/176/1/012029
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    ABSTRACT: We developed a technique to prepare gold nanoparticles (AuNPs) by wire spraying employing a room-temperature atmospheric H2/Ar microplasma jet driven with pulsing ultrahigh frequency and to subsequently deposit the AuNPs on nonheat-resistant materials such as paper in ambient air without apparent damage. In this technique, the application of a pulse waveform with higher voltage but rather low duty cycle effectively lowered the time-averaged gas temperature and facilitated preparing AuNPs. The size, crystallinity, and optical absorption of the prepared AuNPs were characterized, and the derivation and size evolution mechanisms were simply discussed based on the characterizations.
    Applied Physics Letters 05/2009; 94(19):1504-191504. DOI:10.1063/1.3129168 · 3.52 Impact Factor
  • K Kawaguchi · R Wu · Y Ishikawa · T Sasaki · N Koshizaki
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    ABSTRACT: Two unique laser processes of 'PLA in low vacuum (PLALV)' and 'PLA in liquid (PLAL)' have been examined to fabricate FePt nanoparticles and the magnetic and structural properties were investigated. The particles as prepared by PLALV showed a superparamagnetic behavior with an fcc structure. The annealing temperature dependence of the transformation from fcc to fct structure was studied by the structural and magnetic properties. A large coercivity of 3.6 kOe at 300 K was obtained by the low temperature (500 C) annealing. Composition deviation due to Fe dissolution in PLAL process was successfully suppressed by Ar bubbling.
    Journal of Nanoscience and Nanotechnology 03/2009; 9(2):1454-7. DOI:10.1166/jnn.2009.C177 · 1.34 Impact Factor
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    ABSTRACT: Single crystals of calcium ferrite CaFe2O4-type NaTi2O4 having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO2 in a sealed iron vessel at 1473 K. Sodium-deficient NaxTi2O4 single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi2O4 single crystals as parent materials. The crystal structures of NaxTi2O4 with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O6 and Ti2O6 double rutile chains was maintained in these NaxTi2O4 compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti3+ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti3+ and Ti4+ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi2O4 is suppressed by an Na deficiency and vanishes in Na0.717Ti2O4. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na0.799Ti2O4.
    ChemInform 12/2007; 38(52). DOI:10.1002/chin.200752005
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    ABSTRACT: Single crystals of calcium ferrite CaFe2O4-type NaTi2O4 having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO2 in a sealed iron vessel at 1473 K. Sodium-deficient NaxTi2O4 single crystals with 0.558 < x < l were successfully synthesized by a topotactic oxidation reaction using NaTi2O4 single crystals as parent materials. The crystal structures of NaxTi2O4 with x = 0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the TilO(6) and Ti2O6 double rutile chains was maintained in these NaxTi2O4 compounds. Based on the results of bond valence analysis, we speculated that the Til sites are preferentially occupied by Ti3+ cations over the compositional range of 0.8 < x < 1, while both the Ti I and Ti2 sites are randomly occupied by Ti3+ and Ti4+ cations at x = 0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi2O4 is suppressed by an Na deficiency and vanishes in Na0.717Ti2O4. The electrical resistivity increased with the Na deficiency, however, it was still semiconductive in Na0.7999Ti2O4. (c) 2007 Elsevier Inc. All rights reserved.
    Journal of Solid State Chemistry 03/2007; 180(3):1020-1027. DOI:10.1016/j.jssc.2006.12.023 · 2.20 Impact Factor

Publication Stats

721 Citations
166.79 Total Impact Points

Institutions

  • 2002–2015
    • National Institute of Advanced Industrial Science and Technology
      • Electronics and Photonics Research Institute
      Tsukuba, Ibaraki, Japan
  • 2005
    • The University of Tokyo
      • Department of Advanced Materials Science
      Tōkyō, Japan
  • 2003
    • Japan Advanced Institute of Science and Technology
      KMQ, Ishikawa, Japan
  • 1993–2002
    • Tsukuba Research Institute
      Edo, Tōkyō, Japan
  • 1994–1999
    • Keio University
      • Department of Physics
      Edo, Tōkyō, Japan