Osamu Takai

Kanto Gakuin University, Yokohama, Kanagawa, Japan

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Publications (337)651.15 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fiber-shaped cupric oxide (CuO) nanoparticles and flower-shaped ZnO nanoparticles were facilely synthesized by plasma-induced technique directly from copper and zinc electrode pair in water, respectively. The phase composition, morphologies and optical property of nanoparticles have been investigated by energy dispersive X-ray analysis, X-ray powder diffraction, transmission electron microscopy and UV–vis. The in situ analysis by an optical emission spectroscopy clarified the formation mechanism. Plasma was generated from the discharge between a metal electrode pair in water by a pulse direct current power. CuO and ZnO nanoparticles were synthesized via almost the same formation mechanism, which were prepared via the rapid energetic radicals’ bombardment to electrodes’ surface, atom vapour diffusion, plasma expansion, solution medium condensation, and in situ oxygen reaction and further growth. This novel plasma-induced technique will become a potential application in nanomaterials synthesis.
    Plasma Chemistry and Plasma Processing 09/2014; 34(5). · 1.60 Impact Factor
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    ABSTRACT: Epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates using a two-step growth method by ion beam sputter deposition. An STO buffer layer was initially grown on the LAO substrate at a low temperature of 150 °C prior to growing the STO main layer at 750 °C. The thickness of the STO buffer layer was varied at 3, 6, and 10 nm, while the total film thickness was kept constant at approximately 110 nm. According to x-ray structural analysis, we show that the STO buffer layer plays an essential role in controlling the strain in the STO layer grown subsequently. It is found that the strains in the STO films are more relaxed with an increase in buffer layer thickness. Moreover, the strain distribution in two-step grown STO films becomes more homogeneous across the film thickness when compared to that in directly grown STO film.
    Applied Physics Letters 08/2014; 105(5):051911. · 3.52 Impact Factor
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    ABSTRACT: SrTiO3 (STO) thin films were grown on Pt(1 1 1)/Ti/α-Al2O3(0 0 0 1) substrates by ion beam sputter deposition. Growth temperature was varied between 600 and 750 °C, while Ti layer thickness was adjusted from 3 to 36 nm. Experimental results demonstrate that both the crystalline orientation and surface morphology are significantly dependent on change in the growth temperature and Ti layer thickness. From X-ray structural analysis, the STO thin films grown at 600 °C are perfectly (1 1 0)-oriented in spite of the change in Ti layer thickness. The STO thin films with a perfect (1 1 1) orientation are achievable at a sufficiently high growth temperature (≥700 °C) and a thin Ti layer (3–6 nm). Each crystalline orientation of STO thin films has a specific in-plane orientation relationship with respect to the Pt(1 1 1) layer. Flat-, rod-, and triangle-shaped grains are clearly observed from atomic force microscopy investigation, which are associated with the (1 1 0)-, (1 0 0)-, and (1 1 1)-oriented grains, respectively. Their grain orientations also show a good correlation with the X-ray structural analysis. The growth mechanism of each crystalline orientation can be described in term of surface diffusion, surface energy anisotropy, electrostatic, and role of TiOx seeds.
    Applied Surface Science 08/2014; 309:95–105. · 2.54 Impact Factor
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    ABSTRACT: A series of epitaxial SrTiO3 (STO) thin films were grown on (001)-oriented LaAlO3 (LAO) substrates by ion beam sputter deposition (IBSD) at various growth temperatures in the range of 350–800 °C. Our results have shown that the growth temperature plays an essential role in influencing the structural and morphological evolution of the STO thin films. X-ray structural analysis demonstrates that the STO thin films are grown under in-plane compressive strain due to the effect of lattice mismatch. The out-of-plane lattice constant is found to decrease with increasing growth temperature. Atomic force microscopy observation reveals that the growth mode of STO thin films transforms from a three-dimensional island mode to a two-dimensional layer-by-layer mode at a sufficiently high growth temperature of 750 °C. We believe that high-quality epitaxial STO thin films with atomically flat surface prepared by IBSD in this study would be beneficial for the fabrication of perovskite STO-based superlattices.
    Vacuum 07/2014; 109:175. · 1.43 Impact Factor
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    ABSTRACT: The SrTiO3 (STO) thin films were directly grown on Si(111) substrates without buffer layer by an electron-cyclotron-resonance ion beam sputter deposition. The growth temperature was varied from 700°C to 850°C, while other parameters were kept unchanged. X-ray structural analysis demonstrates that the growth temperature has a strong influence in tuning degree of (100) orientation. The STO film grown at 800°C is found to be the highest degree of (100) orientation (98%) and a strong (100) fiber texture. For the surface morphology, the development of plate-shaped grains reveals a good correlation with the change in the degree of (100) orientation. Moreover, the leakage current–voltage characteristics of the Au/STO/Si(111) metal-insulator-semiconductor capacitors are investigated and discussed in considerable detail.
    Journal of the American Ceramic Society 03/2014; · 2.43 Impact Factor
  • Japanese Journal of Applied Physics 12/2013; 52(12R):125101. · 1.06 Impact Factor
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    ABSTRACT: A rapid, one-step process for the synthesis of bimetallic nanoparticles by simultaneous metal reduction and gold erosion in an aqueous solution discharge was investigated. Gold bimetallic nanoparticles were obtained by alloying gold with various types of metals belonging to one of the following categories: divalent sp metals, trivalent sp metals, 3d or 4d metals. The composition of the various gold bimetallic nanoparticles obtained depends on electrochemical factors, charge transfer between gold and other metal, and initial concentration of metal in solution. Transmission electron microscopy and energy dispersive spectroscopy show that the gold bimetallic nanoparticles were of mixed pattern, with sizes of between 5 and 20 nm. A red-shift of the surface plasmon resonance band in the case of the bimetallic nanoparticles Au–Fe, Au–Ga, and Au–In, and a blue-shift of the plasmon band of the Au–Ag nanoparticles was observed. In addition, the interaction of gold bimetallic nanoparticles with unpaired electrons, provided by a stable free radical molecule, was highest for those NPs obtained by alloying gold with a 3d metal.
    Journal of Alloys and Compounds 06/2013; 562:74–83. · 2.73 Impact Factor
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    ABSTRACT: SrTiO3 (STO) thin films were directly grown on Pt(111)/α-Al2O3(0001) substrates without Ti buffer layer using electron cyclotron resonance ion beam sputter deposition. Highly (110)- and (111)-textured STO films were obtained at 600 and 750 °C, respectively. The structural, morphological and electrical properties of both textured films were studied and compared. From high-resolution X-ray diffraction data and in-plane pole figure analysis, highly (110)-textured STO film was found to contain three orientation variants related by a 120° in-plane rotation, while highly (111)-textured STO film had two orientation variants related by a 180° in-plane rotation. The presence of rod- and triangular-shaped grains was observed for the (110)- and (111)-textured film surfaces, respectively. Their grain orientations were also consistent with the structural analysis. The leakage current characteristics of Pt/STO/Pt capacitors were found to follow the Schottky emission and Poole–Frenkel conduction mechanisms. A larger dielectric constant of (111)-textured film (320 at 100 kHz) was obtained in comparison with that of (110)-textured film (238 at 100 kHz) due to the effect of biaxial in-plane tensile strain and larger grain size.
    Solid State Communications 03/2013; 158:65–69. · 1.70 Impact Factor
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    ABSTRACT: As clean and energy saving surface hardening technology, plasma nitriding techniques have been evolved with object of higher performance in the last decades. Even though the diffusion of nitrogen inward to steel is occurred at the final step, solid diffusion from surface, energy transition from gas molecule of nitrogen to atomic or an activated state have many different steps depending on the plasma conditions, parameters and the design of each equipment. And this study made comparative on nitrogen sources transfer with conventional DC plasma nitriding and novel nitriding process using plasma diagnosis and metallurgical observation. With different vacuum pressure, gas ratio and new designed electrode (double-folded screen cathode electrode), it showed a different behavior of DC plasma nitriding including the nano-sized nitride on the outer surface of specimen due to nitrogen source of determining plasma species. In this study, plasma species was able to identify with optical emission spectroscopy (OES) studies. From these observations, we could understand better role of ions or neutral nitrogen species, like neutral nitrogen (N), N2+ and NHx radicals in plasma nitriding process with different parameters. And cutting layers of nitride specimen were showed the results due to a different species gas flow ratio or plasma conditions.
    Journal of Physics Conference Series 03/2013; 417(1):2023-.
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    ABSTRACT: Well-crystallized PtAu alloy clusters of about 2.0 nm in mean diameter are successfully fabricated via a one-step route of solution plasma sputtering at atmospheric pressure. The solution plasma provides a novel reaction field with highly energetic state for the formation of PtAu alloy clusters. The synergetic effects of rapid energetic radicals’ bombardment, atom vapor diffusion, plasma expansion and solution medium condensation resulted in the formation of PtAu alloy clusters with various relative atom amount ratios. PtAu alloy clusters are highly dispersive in water for a long time without any polymeric stabilizer. As-fabricated PtAu alloy clusters show well electrocatalytic activity. PtAu alloy clusters are easily collected and well re-dispersed in various organic solvents for various potential applications. And PtAu alloy clusters supported on carbon were successfully fabricated by a one-step route. These results imply that this novel process will have potential application in future in the design and mass production of various multifunctional metal and/or alloy clusters.
    Journal of Alloys and Compounds 03/2013; 552:351–355. · 2.73 Impact Factor
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    ABSTRACT: The International Conference on Thin Films is the most established conference for all researchers and persons interested in thin films and coatings. It is one of the tri-annual conference series endorsed and co-organized by the Thin Film Division of the International Union for Vacuum Science, Technique and Applications (IUVSTA), a union of national member societies whose role is to stimulate international collaboration in the fields of vacuum science, techniques and applications and related multi-disciplinary topics including solid-vacuum and other interfaces. The 15th International Conference on Thin Films (ICTF-15) is organized by The Vacuum Society of Japan (VSJ) and held at Kyoto TERRSA in Kyoto, Japan on 8-11 November 2011, following the 14th International Conference on Thin Films (ICTF-14), which was held in Ghent, Belgium in 2008. Thin films and coatings are daily becoming increasingly important in the fields of various industries. This International Conference provides a multi-disciplinary forum for recent advances in basic research, development and applications of thin films and coatings. This conference will present a unique opportunity for researchers, engineers and managers to acquire new knowledge of thin films and coatings. We hope that our understanding on thin films and coatings will be deepened through this conference. The conference site, 'Kyoto TERRSA' is located in the historical heart of the old capital Kyoto. Kyoto is an ancient city with a 1200-year history. It was established as Japan's capital under the name 'Heian-kyo' in the year 794. Although many transformations have taken place over the years, Kyoto has always embraced the most advanced standards of the times. It has greatly contributed to the nation's industrial, economic and cultural development. The dauntless spirit of leadership of Kyoto's past as a capital city is still felt here today. Kyoto also preserves the beloved examples of its culture as testimonials of time. This is shown in the ancient temples and shrines, as well as private houses, which are built in styles unique to Kyoto. Furthermore, many festivals, ceremonies and traditional activities reveal the will of this city to convey and develop its 1200-year-old culture. Participants of the conference will also be able to see many world heritage sites in the city. Moreover, November is the best time of year to visit Kyoto. We hope you will enjoy Kyoto very much. We would like to offer our thanks for all the contributions from the members of the International Advisory Committee and Organizing Committee, Symposium Chairs, the Secretary General, the Thin Film Division of IUVSTA (chair: Professor Dr Alberto Tagliaferro), IUVSTA, VSJ and other cooperating societies, and to all of the supporting organizations and enterprises. We would also like to express our thanks to all of the participants, secretariat members and members of the supporting staff. I am very pleased to welcome you to ICTF-15 and Kyoto! Director Professor Dr Osamu Takai Chairperson of ICTF-15 EcoTopia Science Institute, and Department of Materials, Physics and Energy Engineering Graduate School of Engineering Nagoya University Japan
    Journal of Physics Conference Series 03/2013; 417(1):1001-.
  • X. L. Hu, O. Takai, N. Saito
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    ABSTRACT: Gold clusters (average particle size is 1.5 nm) and nanoparticles (average particle size is 3.5 nm) with spherical morphology were fabricated by solution plasma sputtering in solution medium. This process was carried out in an open system under atmospheric pressure. During plasma region, rapid energetic radicals' bombardment, atom vapour diffusion, plasma expansion and medium condensation resulted in the formation of gold nanoparticles from its electrode wires. As-fabricated gold particles have well crystalline even for less than 1 nm cluster. Gold nanoparticles with average size about 3.5 nm gave obviously surface plasmon resonance band at near 511 nm. While surface plasmon resonance band was disappearing for 1.5 nm-cluster formed in liquid nitrogen.
    Journal of Physics Conference Series 03/2013; 417(1):2030-.
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    ABSTRACT: Epitaxial oxide superlattices (SLs) of SrTiO3 (STO) and Nb-doped SrTiO3(STNO) were fabricated on LaAlO3 (LAO) (001) substrates by an ion beam sputter deposition (IBSD) system having double electron cyclotron resonance (ECR) ion guns. The [STOx/STNOy]10 SLs were epitaxially grown at different stacking sequences (x = 6 nm, y = 1–6 nm) and maintained the periodicity z of 10. Structural properties and surface morphology are found to be strongly dependent on the STNO sublayer thickness (y). Highly strained SLs with two-dimensional growth mode is observed at smaller STNO sublayer thickness (y = 1 nm). With increasing to a critical thickness (y = 4 nm), the SLs are freely strained and transformed to three-dimensional growth mode. The results demonstrate that the double ECR-IBSD is a versatile technique for the growth of high-quality oxide SLs.
    Vacuum 03/2013; 89:35–39. · 1.43 Impact Factor
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    ABSTRACT: SrTiO3 (STO) thin films have been deposited on glass substrates by electron cyclotron resonance (ECR) ion beam sputter deposition at different substrate temperatures (100–600 °C). The structural characteristics of the deposited films show a transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit good transparency with an interference pattern in the visible region and a very smooth surface without cracks. The refractive index of the films increases with an increase of the substrate temperature, and their dispersion was analyzed by a single-oscillator model. The extinction coefficient of the films in the visible region is of the order of 10−3–10−2. The estimated values of the direct and indirect bandgap energies for the polycrystalline STO film are 3.80 and 3.32 eV, respectively. Its density is almost identical to the bulk STO single crystal, which is relatively high in comparison with those prepared by other techniques. The mechanical stability of the films is also improved with an increase of substrate temperature. Young's modulus and hardness of the polycrystalline STO film are 194.1 ± 15.5 and 22.5 ± 2.0 GPa, respectively.
    physica status solidi (a) 02/2013; 210(2):311-319. · 1.21 Impact Factor
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    ABSTRACT: Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λ = 4.8 - 48 nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect.
    Applied Physics Letters 01/2013; 103(11):112902-112902-4. · 3.52 Impact Factor
  • Takahiro Ishizaki, Osamu Takai
    Journal of The Surface Finishing Society of Japan 01/2013; 64(8):425-428.
  • Journal of Photopolymer Science and Technology 01/2013; 26(4):507-511. · 0.91 Impact Factor
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    ABSTRACT: Transparent SrTiO3 thin films were deposited on glass substrates by ion beam sputtering at various substrate temperatures. The structural characteristic of the deposited films shows the transition from amorphous phase to polycrystalline phase at 600 °C. The films exhibit a good transparency in the visible region (~80-85%) and a relatively smooth surface. The calculated band gaps for amorphous and polycrystalline films were ~4.20 and ~3.84 eV, respectively. The refractive index of the films increases with increasing the substrate temperature, and the extinction coefficient of the films in the visible region is in the order of 10−3, indicating low optical loss. The nanomechanical properties of the films were investigated using nanoindentation technique. Young’s modulus and hardness for all films are found to be increased with the increase of substrate temperature.
    Journal of Materials Engineering and Performance 01/2013; 22(3). · 0.98 Impact Factor
  • Xiulan Hu, Osamu Takai, Nagahiro Saito
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    ABSTRACT: We applied a novel method of plasma sputtering in water for simple and fast preparation of carbon-supported platinum nanoparticles at atmospheric pressure from platinum wire electrodes without using any stabilizers, chemical reductant, plasma-generating gas, or salt solution in an open system. Upon plasma sputtering, special waveforms of voltage and current were obtained using a pulsed power supply. The obtained emission spectra clarified that platinum atoms were formed in the plasma region from the electrode surface owing to bombardment of the surface by highly energetic electrons and radicals derived from plasma. Thus, carbon-supported 2 nm and highly dispersed platinum nanoparticles were successfully synthesized by this fast and simple plasma sputtering method. Highly crystallized platinum nanoparticles show good electrocatalytic activity. This plasma sputtering technique has shown a potential application to the synthesis of other metal nanoparticles.
    Japanese Journal of Applied Physics 01/2013; 52(1). · 1.06 Impact Factor
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    G. Panomsuwan, O. Takai, N. Saito
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    ABSTRACT: SrTiO3 (STO) thin films were grown on Pt/Al2O3 substrates without a Ti adhesion layer by an ion beam sputter deposition method in a range of growth temperatures between 600 and 750 °C. The effect of growth temperature on the film orientation was investigated by high-resolution x-ray diffraction, pole figure measurements and in-plane grazing incidence x-ray diffraction. The film orientation showed a strong dependence on the growth temperature. The films exhibited a predominant (1 1 0) orientation at a low growth temperature of 600 °C. With an increase in growth temperature to 750 °C, a highly (1 1 1)-textured STO film with two different orientation variants was achieved on the Pt/Al2O3 substrate. A narrow full-width at half-maximum of 0.12° for the rocking curve measured on 2 2 2STO reflection and a six-fold symmetry from {1 0 0}STO and {1 1 0}STO pole figures were observed. Three-dimensional island growth mode was observed on the surfaces of all films, as investigated with an atomic force microscope. The evolution of grain shape and size was apparently found with an increase in growth temperature. The root-mean-square roughness of the STO film grown at 750 °C was raised to be about 4 nm due to the surface faceting of (1 1 1)-oriented grains. The growth mechanism of the (1 1 0)- and (1 1 1)-textured STO films on the Pt/Al2O3 substrates was also explained and discussed in detail.
    Journal of Physics D Applied Physics 12/2012; 45(49):4003-. · 2.52 Impact Factor

Publication Stats

4k Citations
651.15 Total Impact Points

Institutions

  • 2013–2014
    • Kanto Gakuin University
      Yokohama, Kanagawa, Japan
  • 1996–2013
    • Nagoya University
      • • Department of Materials, Physics and Energy Engineering
      • • EcoTopia Science Institute
      • • Graduate School of Engineering
      • • Center for Integrated Research in Science and Engineering (CIRSE)
      Nagoya, Aichi, Japan
  • 2004
    • Kanagawa Academy of Science and Technology
      Kawasaki Si, Kanagawa, Japan
  • 2003
    • Gifu Pharmaceutical University
      • Laboratory of Pharmaceutical Physical Chemistry
      Nagoya, Aichi, Japan