Osamu Takai

Kanto Gakuin University, Kawasaki Si, Kanagawa, Japan

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Publications (378)702.49 Total impact

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    ABSTRACT: We discussed the electron impact dissociation behavior of the organosilicon molecules with methyl groups, based on the fragment pattern and molecular-orbital calculation of the bond dissociation energies for the molecules. From the calculation of bond dissociation energy of the organosilicon molecules, methyl groups, which bonded directly to the silicon atom, were found to have the weakest. Regarding the fragment patterns of the reactants investigated by a quadrupole mass spectrometer, the hexamethyldisiloxane was harder to dissociate than the trimethylmethoxysilane due to the strong Si–O bonding force, which also affected the dissociation in the plasma. From the above considerations, dissociation reactions by electron impact could be partly identified.
    No preview · Article · Dec 2014 · Journal of Nanoscience and Nanotechnology
  • Osamu Takai
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    ABSTRACT: Liquid-phase plasma is not well known compared with gas-phase plasma. We name the liquid-phase plasma “solution plasma” because of the generation of different plasmas by choosing the combinations of solvents and solutes in solutions. We can generate a glow discharge with a pulsed power generator by controlling several parameters for the ignition of the discharge. It is important to generate the glow discharge in solutions, which realizes the formation of a new reaction field at almost room temperature. We measured the basic physical and chemical properties of solution plasma by time-resolved optical spectroscopy and coherent ant-Stokes Raman spectroscopy (CARS). The solution plasma is applicable to nanomaterials synthesis, surface modifications, water treatment, sterilization, decomposition of cellulose and toxic compounds, and so far.
    No preview · Article · Sep 2014 · Journal of Photopolymer Science and Technology
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    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.
    No preview · Article · Sep 2014 · Plasma Chemistry and Plasma Processing
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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.
    Full-text · Article · Aug 2014 · Applied Physics Letters
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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.
    Full-text · Article · Aug 2014 · Applied Surface Science
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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.
    Full-text · Article · Jul 2014 · Vacuum
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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.
    Full-text · Article · Mar 2014 · Journal of the American Ceramic Society
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    ABSTRACT: Three-dimensionally integrated micro-solution plasmas (3D IMSPs), in which microplasmas are generated in gas bubbles in an aqueous solution held in a porous dielectric material, have been applied to gold nanoparticle synthesis. Conventional solution plasma processes require additional chemicals to increase the electrical conductivity of the aqueous solution for generating plasmas. In contrast to this, 3D IMSPs have been found to generate plasmas without such a procedure when the aqueous solution has a low electrical conductivity as in the case of HAuCl4 for gold nanoparticle synthesis. The gold nanoparticle synthesis has been confirmed through the observation of optical absorption due to the plasmon resonance at 550 nm, and also through the characterization of their size, crystallinity, and composition by transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2013 The Japan Society of Applied Physics
    No preview · Article · Dec 2013 · Japanese Journal of Applied Physics
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    ABSTRACT: Solution plasma processing (SPP) has beern performed on multiwalled carbon nanotubes (MWCNTs) in ammonia aqueous solution. The MWCNTs, which do not disperse in aqueous solution, uniformly dispersed after the SPP. Only 2h was required to obtain log of the dispersed MWCNTs, while 7 days and additional chemicals were required for 185 mg in a previous study. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the SPP-treated MWCNTs revealed that nitrogen- and oxygen-containing groups are formed on the MWCNTs. Serious damage to the MWCNT structure was not observed in the Raman spectrum or transmission electron microscopy images of the SPP-treated MWCNTs. The composite materials prepared using polyamide 6 with the SPP-treated MWCNTs Showed better tensile, bending, and impact strength than those prepared with nontreated MWCNTs. (C) 2013 The Japan Society of Applied Physics
    No preview · Article · Dec 2013 · Japanese Journal of Applied Physics
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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.
    Full-text · Article · Sep 2013 · Applied Physics Letters
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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.
    Full-text · Article · Jun 2013 · Journal of Alloys and Compounds
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    ABSTRACT: Clean, nanosized PtAu/C catalysts were fabricated, using a simple one-step synthesis technique that involved sputtering discharge in liquid, and did not require the use of chemical species such as surfactants and/or reductants. This solution plasma sputtering was driven by a pulsed power supply, and was performed on the discharge between Pt and Au targets in a liquid dispersion of carbon black. Fine PtAu nanoparticles with an average diameter of 5.7 nm were uniformly deposited on the carbon support. The production and composition of the PtAu nanoparticles could be controlled via changes in the sputtering conditions. The Au-rich Pt19Au81/C (atomic %) catalysts provided higher specific capacity, even in carbonate-based electrolyte Li-air batteries, reducing the amount of Li2CO3 that was deposited on the bare carbon.
    No preview · Article · Apr 2013 · International journal of electrochemical science
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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
    No preview · Article · Mar 2013 · Journal of Physics Conference Series
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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.
    Full-text · Article · Mar 2013 · Journal of Physics Conference Series
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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.
    Full-text · Article · Mar 2013 · Vacuum
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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.
    No preview · Article · Mar 2013 · Journal of Materials Engineering and Performance
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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.
    Full-text · Article · Mar 2013 · Solid State Communications
  • Xiulan Hu · Xiaodong Shen · Osamu Takai · Nagahiro Saito
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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.
    No preview · Article · Mar 2013 · Journal of Alloys and Compounds
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    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.
    Preview · Article · Mar 2013 · Journal of Physics Conference Series
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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.
    Full-text · Article · Feb 2013 · physica status solidi (a)

Publication Stats

6k Citations
702.49 Total Impact Points

Institutions

  • 2013-2014
    • Kanto Gakuin University
      Kawasaki Si, Kanagawa, Japan
    • Japan Science and Technology Agency (JST)
      Edo, Tokyo, 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
  • 2001
    • Nagoya Municipal Industrial Research Institute
      Nagoya, Aichi, Japan
    • Universitatea Alexandru Ioan Cuza
      • Faculty of Physics
      Socola, Iaşi, Romania