Katsuya Teshima

Shinshu University, Shonai, Nagano, Japan

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Publications (131)406.1 Total impact

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    ABSTRACT: Copper–indium–gallium–sulfide–selenide (CIGSSe) is used in photovoltaic cells and photocathodes, because of its tunable optoelectronic properties, but the fabrication of CIGSSe samples usually requires a multistage process under vacuum. Herein we used a flux growth technique for the sulfide system and achieved efficient flux growth of idiomorphic copper–indium–sulfide CuInS2 crystals of size ~5 μm from a NaCl–InCl3 flux under mild conditions at ambient pressures. We first examined the flux growth conditions such as holding temperature, solute concentration, and holding time for growing highly crystalline CuInS2 crystals. A moderate holding temperature (~550 °C) and high solute concentration (~70 mol%) yielded idiomorphic pure CuInS2 crystals. High-resolution transmission electron microscopy showed clear electron diffraction spots, indicating that the resultant CuInS2 crystals had a highly crystalline, intrinsic tetragonal crystal structure. Thermogravimetry-differential thermal analysis showed that the CuInS2 crystals grew efficiently during flux evaporation at 550 °C, at which the flux evaporation degree reached ~81%. The CuInS2 crystal growth mode is discussed based on the characterization results.
    No preview · Article · Jan 2016 · Crystal Growth & Design
  • Sayaka Suzuki · Hajime Wagata · Kunio Yubuta · Shuji Oishi · Katsuya Teshima
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    ABSTRACT: Orthorhombic NaTaO3 crystals were epitaxially grown on a SrTiO3 (100) surface using flux coating. The selected-area electron diffraction results revealed that the well-oriented orthorhombic NaTaO3 crystals and SrTiO3 had an orientation relationship of (10-1)[010] NaTaO3//(100)[010] SrTiO3.
    No preview · Article · Nov 2015 · CrystEngComm
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    ABSTRACT: We demonstrate a new way to prepare hollow-structured LiCoO2 crystals directly on a Pt substrate for the first time through a combination of semi-additive electrodeposition of a Co core and subsequent flux growth in molten LiNO3. The reaction process was characterized by time-dependent X-ray diffraction and scanning electron microscopy. The vertically oriented crystals having a platelet shape grew densely on the Co dot surface. The crystal growth was driven by supersaturation in the same manner as the flux growth. Significantly slower oxidation of the Co core and rapid lithiation of Co3O4 lead to pore formation, which suggests that slow oxygen diffusion in the Co core is rate limiting. Galvanostatic tests revealed that the LiCoO2 crystal array exhibited typical capacity–voltage profiles with no heavy capacity loss during the first three cycles without any additives.
    No preview · Article · Nov 2015 · RSC Advances
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    ABSTRACT: In this study, we have attempted to experimentally validate the results of previous theoretical calculations predicting the possible formation of the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases by applying conventional one- and two-step fabrication methods under an NH3 flow. For the two-step method, CdTiO3, Cd2Nb2O7, and Cd2Ta2O7 crystals were first grown by a KCl flux method, and the effects of solute concentration and cooling rate on the crystal growth were studied. The formability of their (oxy)nitride derivatives was investigated by changing the nitridation temperature (750 to 950 °C) and time (1 to 10 h) of oxide precursors. It was found that the CdTiO3-xNy, CdNbO2N, and CdTaO2N phases cannot be formed by the applied methods due to the low volatilization temperature of cadmium and the susceptibility of titanium and niobium to reduction under an NH3 atmosphere. Under high-temperature NH3 atmosphere, only Cd2Ta2O7 was fully converted to single-phase Ta3N5. The results from the photocatalytic O2 evolution test over bare and CoOx-loaded Ta3N5 crystalline structures, converted from Cd2Ta2O7 (Cd-Ta3N5) and Na2CO3-treated Ta2O5 (Na-Ta3N5) and Cd2Ta2O7 (Na-Cd-Ta3N5) crystals by nitridation at 850 °C for 20 h under an NH3 flow, revealed that the CoOx-loaded Na-Ta3N5 showed more than two times higher O2 evolution rate (655 μmol), whereas the CoOx-loaded Cd-Ta3N5¬ and Na-Cd-Ta3N5¬ exhibited nearly four (501 μmol) and three (422 μmol) times higher O2 evolution rates at 5 h compared with their bare counterparts. An improved photocatalytic activity for O2 evolution is related to the higher density of nucleation centers of CoOx nanoparticles in the form of dangling bonds in porous Ta3N5 structures and long-lived photogenerated holes, as attested by time-resolved absorption spectroscopy.
    No preview · Article · Oct 2015 · Applied Catalysis B: Environmental
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    ABSTRACT: Garnet-type Li5+xLn3MIV2-yMVyO12+z (x, y = 0-2, z = 0-1; Ln = La, Pr, Nd; M = Ta, Zr, Nb) compounds are promising Li-ion conducting solid electrolytes, but their growth manner is still unclear. Herein, the analysis of the low-temperature growth of idiomorphic Li5La3Ta2O12 single crystals as a function of holding temperature and time, cooling rate, flux type, and solute concentration revealed a unique growth manner. Li5La3Ta2O12 crystals were grown at 500 °C from LiOH flux and transformed into Li7La3Ta2O13 at 700 °C. The pseudo-perovskite-type LiLa2TaO6 phase, initially formed during the holding at 500 °C, was efficiently transformed into the Li5La3Ta2O12 phase with increasing holding time. The growth of Li5La3Ta2O12 single crystals was independent of the cooling rate but was affected by the kind of flux and solute concentration. A low solute concentration (1 or 5 mol %) was the key to obtain well-dispersed and idiomorphic single crystals. The optimum growth conditions involved a holding temperature of 500 °C, a solute concentration of 1 or 5 mol %, and a holding time of 10 h. These findings indicate that formation and growth of Li5La3Ta2O12 single crystals are not only controlled by a general flux growth process but also involve chemical reactions between solutes and LiOH flux. Finally, high-resolution transmission electron microscopy image and selected area diffraction pattern highlighted products with high crystallinity and well-developed {110} and {211} facets.
    No preview · Article · Aug 2015 · Crystal Growth & Design
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    ABSTRACT: As the 600 nm-class photocatalyst, BaTaO2N is one of the promising candidates of the perovskite-type oxynitride family for photocatalytic water splitting under visible light. The oxynitrides are routinely synthesized by nitriding corresponding oxide precursors under a high-temperature NH3 atmosphere, causing an increase in the defect density and a decrease in photocatalytic activity. To improve the photocatalytic activity by reducing the defect density and improving the crystallinity, we here demonstrate an NH3-assisted KCl flux growth approach for the direct synthesis of the BaTaO2N crystals. The effects of various fluxes, solute concentration, and reaction time and temperature on the phase evolution and morphology transformation of the BaTaO2N crystals were systematically investigated. By changing the solute concentration from 10 to 50 mol %, it was found that phase-pure BaTaO2N crystals could only be grown with the solute concentrations of ≥ 10 mol % using the KCl flux, and the solute concentration of 10 mol % was solely favorable to directly grow cube-like BaTaO2N crystals with an average size of about 125 nm and exposed {100} and {110} faces at 950 °C for 10 h. The time- and temperature-dependent experiments were also performed to postulate the direct growth mechanisms of cube-like BaTaO2N submicron crystals. The BaTaO2N crystals modified with Pt and CoOx nanoparticles showed a reasonable H2 and O2 evolution, respectively, due to a lower defect density and higher crystallinity achieved by an NH3-assisted KCl flux method.
    No preview · Article · Jul 2015 · Crystal Growth & Design
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    ABSTRACT: Olivine-type LiFePO4 has been an interesting material in the development of catalysts and lithium-ion rechargeable batteries. In this study, we propose a new method for growing thin films of LiFePO4 crystals directly on SUS substrates using flux coating. Molten NaCl-KCl flux promoted the formation of individual LiFePO4 crystals with well-defined facets surrounded by {100}, {110}, and {201} faces and highly oriented along the [100] direction. The LiFePO4 crystals attached tightly to the SUS substrate, implying that crystal growth began directly at the SUS surface via heterogeneous nucleation, driven by supersaturation in the NaCl-KCl flux. We further demonstrated the formation of LiFePO4 crystal films using an infrared light-heating furnace system, which reduced the fabrication time from several hours to less than 30 min. Rapid heating and cooling effectively suppressed the corrosion of the SUS substrate caused by the NaCl-KCl flux. (Figure Presented).
    No preview · Article · Jul 2015 · Crystal Growth & Design
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    ABSTRACT: In this study, we demonstrated the template-mediated flux growth of one-dimensional LiCoO2 single crystals surrounded by {104} faces in a hot solution of LiCl-KCl. The reaction and growth process were characterized by time-dependent X-ray diffraction and scanning electron microscopy. The transformation in the crystal shape from rectangular to hexagonal cylindrical was considered to be directly related to the gradual lithiation of the starting CoO whiskers. Single particle galvanostatic tests of the single-strand LiCoO2 crystals were carried out. The LiCoO2 crystals exhibited excellent rate performance; more than 65% of the full capacity was maintained under ca. 370 C. These characteristics likely resulted from the exposure of the {104} planes, since they were electrochemically active in layered LiCoO2 with an α-NaFeO2 structure and favored fast Li+ transportation. This finding will facilitate the development of new materials for advanced lithium ion rechargeable batteries.
    No preview · Article · Jun 2015
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    ABSTRACT: Photocatalytic overall water splitting on (oxy)nitrides under visible light is one of the interesting approaches to fulfill the growing demand for clean and renewable energy. The improvement of the fabrication method is however important for reducing the defect density of (oxy)nitride crystals. The present study aims to investigate the direct growth of the LaTiO2N (LTON) crystallites with less defect density by an NH3-assisted flux method and to demonstrate the visible-light-induced photocatalytic water oxidation activity in relation to their crystallite morphology. Single-phase LaTiO2N crystallites (average size of 120 ± 39 nm) in round shape with smooth surface and high crystallinity were grown by an NH3-assisted flux method using the KCl flux with the solute concentration of 5 mol % at 950 °C for 10 h. The photocatalytic water oxidation activity of bare and CoOx-loaded LaTiO2N crystallites grown directly by an NH3-assisted flux method (1-step-LTON) was evaluated under visible light by comparing with the LaTiO2N crystallites fabricated by a two-step method (2-step-LTON), converting La2Ti2O7 to LaTiO2N by high-temperature nitridation. Within the first 2 h of the photocatalytic water oxidation half-reaction, the O2 evolution rates of bare and CoOx-loaded 1-step-LTON crystallites were 82 μmol·h-1 and 204 μmol·h-1, respectively, which are much higher than that of bare and CoOx-loaded 2-step-LTON crystallites (37 μmol·h-1 and 177 μmol·h-1) due to less defect density of the LaTiO2N crystallites achieved by a direct fabrication route using KCl flux. An NH3-assisted flux growth is a promising route for the direct fabrication of the LaTiO2N crystallites with less defect density that is beneficial for the enhancement of photocatalytic water oxidation half-reaction.
    No preview · Article · Jun 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Layers of well-developed crystals of Ta3N5 were successfully fabricated on Ta substrates by a novel flux coating method in a flow of NH3. The flux coating method is a simple one: the Ta substrates were coated with aqueous solutions of sodium compounds (= fluxes) and subsequently heated in a flow of NH3, whereupon the surfaces of the Ta substrates were dissolved in the flux, resulting in Ta3N5 crystal layers. The Ta in the Ta3N5 was provided by the substrate. Therefore, crystal layers with good adhesion could be grown directly on the substrates. The shape of the individual crystals as well as the surface morphology of the layers formed was determined by the flux used. The crystals fabricated using NaCl-Na2CO3 as the flux were prismatic and had relatively smooth faces, covering the surface of the Ta substrate uniformly. The crystal growth field resulting from the use of this method yielded well-formed crystals, which presumably grew from a solution. Finally, it was confirmed that a thus-synthesized Ta3N5 crystal layer modified using Co-Pi as the cocatalyst generated a photoanodic current under visible-light irradiation.
    No preview · Article · May 2015
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    ABSTRACT: The thin films consisting of crystalline ZnO particles were prepared on FTO electrodes by electroless deposition. The particles were deposited from an aqueous solution containing zinc nitrate, dimethyamine-borane, and eosin Y at 328K. As the Pd particles were adsorbed on the substrate, not only the eosin Y monomer, but also the dimer and debrominated species were rapidly adsorbed on the spherical ZnO particles, which were aggregated and formed secondary particles. On the other hand, in the absence of the Pd particles, the monomer was adsorbed on the flake-shaped ZnO particles, which vertically grew on the substrate surface and had a high crystallinity. The photoelectric conversion efficiency was higher for the ZnO electrodes containing a higher amount of the monomer during light irradiation.
    No preview · Article · May 2015 · ACS Applied Materials & Interfaces
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    ABSTRACT: The phase-selective synthesis of (Li1.81H0.19)Ti2O5·2H2O flakes and homogenous LiTiO2 spheres has been achieved by means of a hydrothermal method using a titanium-triethanolamine complex. Compared with other Ti sources this offers the advantage of being more stable in water, though the crystal phases obtained depend on the growth conditions used, such as the initial Li/Ti ratio and aging time. The (Li1.81H0.19)Ti2O5·2H2O flakes were obtained through aging at 250 °C for 3 h from an initial Li/Ti ratio of 1.0 and exhibited a large surface area of 135 m2 g−1. Subsequent heat treatment of these flakes yielded Li4Ti5O12 nanoparticles with an even larger surface area (141 m2 g−1) and a discharge capacity of 164 mAh g−1, making them suited for use as an active material in lithium-ion rechargeable batteries.
    No preview · Article · May 2015 · Ceramics International
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    ABSTRACT: Dye-dispersing allophane–titania composite electrodes were prepared from titanium alkoxide sols containing dye and allophane. The photoelectric conversion properties of the electrodes were investigated by photoelectrochemical measurements. The photocurrent values in the UV range decreased with an increase in the allophane content, whereas those in the visible range were increased by adding 1.0% (Al/Ti ratio) allophane. As a small amount of allophane nanoparticles were highly dispersed in the titania electrodes, the dye molecules were dispersed in the electrodes without decreasing the efficiency of the electron injection from the dye to the titania conduction band. The dye molecules dispersed on the titania nanoparticle surface were capped with allophane nanoparticles which prevented desorption. The dye molecules strongly interacted with the titania nanoparticle surface and efficiently injected the excited electrons into the titania conduction band.
    No preview · Article · Apr 2015 · Applied Clay Science
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    ABSTRACT: Defect formation energies based on an oxygen vacancy model and a metal-excess model in Ni/Mn ordered P4332 and disordered Fd3-m LiNi0.5Mn1.5O4 (LNMO) were evaluated by using ab initio density functional theory (DFT) calculations. The defect formation energy for the metal excess model was lower than for the oxygen vacancy model in both P4332 and Fd3-m. This indicates that oxygen vacancy formation reactions are unlikely, although interstitial cation occupation at the octahedral vacancies occurred in both P4332 and Fd3-m LNMO spinel compounds. In addition, the corresponding defect formation energy in Fd3-m was lower than that in P4332, indicating that the amount of defects is sensitive to the cation ordering/disordering in the spinel framework. This agrees with the experimental results that show that only Fd3-m tends to possess oxygen defects.
    No preview · Article · Apr 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Micrometer-sized Li7La3Zr2O12 crystals with well-developed facets were grown from a LiOH flux at 700 °C. Supersaturation-controlled crystallization driven by the cooling of a homogeneous hot solution with a Li/Zr ratio of 70 achieved one-step formation of cubic-phase Li7La3Zr2O12 that potentially exhibits high lithium-ion conductivity. Excess LiOH flux decreased the reaction temperature dramatically to 700 °C, lower than that of solid-state-reaction processes. The flux growth of the Li7La3Zr2O12 crystals in response to varying reaction conditions was studied systematically and indicated that the initial Li/Zr ratio and the holding temperature significantly affected the crystal phase, shape, and size. We further demonstrated Li7La3Zr2O12 crystal growth at 500 °C, beginning with La2Zr2O7 powders that dissolve readily in hot LiOH. This will be examined in greater depth in the near future.
    No preview · Article · Mar 2015 · CrystEngComm
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    ABSTRACT: Flux growth is a promising method that allows to control both crystalline phase and crystal shape through the selection of a suitable flux. In this work, lanthanum titanate (La2Ti2O7) crystals with different morphologies were grown using the Na2MoO4, K2MoO4, NaCl, and mixed NaCl+K2MoO4 (molar ratio = 3:7) fluxes and their nitridability to form the LaTiO2N crystals under a high-temperature NH3 atmosphere was also investigated. The effects of solute concentration and cooling rate on the growth of the La2Ti2O7 crystals were also studied. The XRD results revealed that the {100} plane was dominant in the La2Ti2O7 platelet crystals grown using the alkali metal molybdate fluxes. By increasing the solute concentration from 1 to 20 mol%, an average size of the crystals decreased without considerably altering the overall crystal morphology. The La2Ti2O7 crystals with the preferred <010> and <001> growth directions along the b and c axes were grown using the Na2MoO4 and K2MoO4 fluxes, respectively. Compared to the Na2MoO4 flux, the K2MoO4 flux did not show a cooling rate-dependent effect on the growth of the La2Ti2O7 crystals. It was found that the conversion of the La2Ti2O7 crystals into the LaTiO2N crystals was strongly dependent on the flux used to grow the precursor La2Ti2O7 crystals. That is, the La2Ti2O7 crystals grown using the K2MoO4 and NaCl fluxes were nearly completely converted into the LaTiO2N crystals, while the conversion of the La2Ti2O7 crystals grown using the Na2MoO4 and mixed NaCl+K2MoO4 fluxes into the LaTiO2N crystals seemed to be not completed yet even after nitridation at 950°C for 15 h using NH3 due to the larger crystal size and the presence of unintentional impurities (Na and Mo from the flux) in the La2Ti2O7 crystal lattice. Nevertheless, the LaTiO2N crystals fabricated by nitriding the La2Ti2O7 crystals grown using the K2MoO4 and NaCl fluxes should be suitable for the direct solar water splitting.
    No preview · Article · Mar 2015 · Inorganic Chemistry
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    ABSTRACT: Layered double hydroxide (LDH) is an environmentally benign anion exchanger that can adsorb various toxic anions. In this work, we demonstrate the fabrication of plate-like Mg-Al-type LDH crystals on in situ formed alumina particles using a flux method at a relatively low temperature (∼350 °C). At or below 300 °C, the melted Al source crystallized to form AlOOH or γ-alumina particles in KNO3-NaNO3 flux. However, LDH crystals did not form due to the inferior crystallization properties of the Mg precursor. Increasing the holding temperature up to 350 °C and above facilitated crystallization of the dissolved Mg and Al species in flux to yield plate-like LDH crystals on the preformed alumina particles. Top-surface and cross-sectional FE-SEM and EPMA analyses revealed the vertical alignment of the crystalline LDH plates on the surface of the alumina particles. On the other hand, solid-state reactions did not yield these well-grown, plate-like LDH crystals. The TG-DTA profile of the LDH precursors with flux depicted the decomposition and crystallization events that the Al and Mg precursors undergo. On the basis of the results from these characterization studies, we propose a mechanism in which LDH crystals sequentially form on the surface of the alumina particles.
    No preview · Article · Feb 2015 · Crystal Growth & Design
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    ABSTRACT: Highly crystalline, platelike La(2)Ti(2)O7 were grown from a NaCl flux, and LaTiO2N crystals were obtained by subsequent nitridation under NH3 flow. The TEM analysis indicated that the flux-grown platelike La2Ti2O7 crystals are single-crystalline growing along the a axis. The shapes and sizes of the LaTiO2N crystals were almost unchanged from the La2Ti2O7 precursor. In addition, LaTiO2N crystals remained single-crystalline with a porous nanostructure. The optical absorption edges of the La2Ti2O7 and LaTiO2N crystals were approximately 320 and 600 nm.
    No preview · Article · Jan 2015 · Crystal Growth & Design
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    ABSTRACT: Oxynitride perovskites and related phases have received considerable attention due to their potential application for visible-light-responsive photocatalyst and nontoxic inorganic pigments. The changes in bonding and structure by a partial replacement of O2– by N3– give rise to interesting dielectric behavior. Here, we report on the fabrication of highly crystalline La2TiO5 crystals by chloride flux growth method and their subsequent nitridation to form the LaTiO2N crystals using NH3 gas. The flux-grown La2TiO5 crystals had a columnar structure grown in the ⟨001⟩ direction. Using the NaCl flux, larger columnar La2TiO5 crystals were grown compared to those grown using the KCl flux. With increasing solute concentration, the aspect ratio of columnar La2TiO5 crystals decreased significantly. The columnar La2TiO5 crystals with smooth surface were readily converted by nitridation at 950 °C for 45 h followed by acid treatment into the LaTiO2N crystals with a highly porous structure that formed from the strong segregation of nanocrystals, leading to the largest specific surface area (16.5–18.4 m2·g–1). For the La2TiO5 crystals grown using the chloride fluxes, the wavelength of the absorption edges was approximately 320 nm (Eg = 3.87 eV), whereas the absorption edges exhibited by the LaTiO2N crystals obtained by nitridation were approximately 600 nm (Eg = 2.06 eV). Particularly, the LaTiO2N crystals prepared in this study by nitriding the precursor La2TiO5 crystals did not show a noticeable absorption in the near-infrared region above 600 nm, which is generally attributable to some reduced Ti3+ species and nitrogen deficiency, even after a long nitridation process. The fabricated LaTiO2N crystals with low defect density will be advantageous for various applications that specially require higher specific surface area.
    No preview · Article · Jan 2015 · Crystal Growth & Design
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    ABSTRACT: Zinc oxide and layered zinc hydroxides were deposited from an aqueous solution of zinc nitrate at 323-358 K on a substrate plate with a very thin titanium dioxide film by a photocatalytic reaction. The amorphous or low crystalline zinc hydroxide aggregates were deposited at a low temperature. The zinc oxide crystals with about 1-2 μm-sized hexagonal columns and 10 nm-sized spheres were formed at 338-358 K. Nitrate ions in the solution were reduced to nitrite ions, and water was transformed into hydroxide ions by a photocatalytic reaction on the titanium dioxide film. The pH value increased on the substrate surface with the titanium dioxide film, which caused the zinc hydroxide formation on the film. The zinc hydroxides were then dehydrated and transformed into zinc oxide. The average crystallite size of the zinc oxide decreased with an increase in the reaction temperature because the reaction rates of the formation and dehydration of the zinc hydroxides increased which resulted in an increase in the formation rate of the crystal zinc oxide nuclei.
    No preview · Article · Nov 2014 · Applied Catalysis B Environmental

Publication Stats

1k Citations
406.10 Total Impact Points


  • 2004-2015
    • Shinshu University
      • • Faculty of Engineering
      • • Department of Environmental Science and Technology
      Shonai, Nagano, Japan
  • 2002-2005
    • Dai Nippon Printing
      Edo, Tokyo, Japan
  • 2001-2003
    • Nagoya University
      • Graduate School of Engineering
      Nagoya, Aichi, Japan