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Hokkaido University Collection of Scholarly and Academic Papers (135.521 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 20 de 23

  1. Photochemistry and the role of light during the submerged photosynthesis of zinc oxide nanorods

    Zhang, Lihua; Jeem, Melbert; Okamoto, Kazumasa; Watanabe, Seiichi
    Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO nanostructures have been successfully fabricated via this method. However, the photochemical reactions involved in the SPSC process and especially the role of light are still unclear. In the present work, we discuss the reaction mechanism for SPSC-fabricated ZnO nanostructures in detail and clarify the role of light in SPSC. The results show that both photoinduced reactions and hydrothermal reactions are involved in the SPSC process. The former produces OH radicals, which is the main source of OH− at the...

  2. Twin formation in hematite during dehydration of goethite

    Saito, Genki; Kunisada, Yuji; Nomura, Takahiro; Sakaguchi, Norihito; Akiyama, Tomohiro
    Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 degrees C, a phase transformation occurred at temperatures above 250 degrees C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001](G) was transformed into hematite with a growth direction of [100](H). Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 degrees C, the majority...

  3. Twin formation in hematite during dehydration of goethite

    Saito, Genki; Kunisada, Yuji; Nomura, Takahiro; Sakaguchi, Norihito; Akiyama, Tomohiro
    Twin formation in hematite during dehydration was investigated using X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy (TEM). When synthetic goethite was heated at different temperatures between 100 and 800 degrees C, a phase transformation occurred at temperatures above 250 degrees C. The electron diffraction patterns showed that the single-crystalline goethite with a growth direction of [001](G) was transformed into hematite with a growth direction of [100](H). Two non-equivalent structures emerged in hematite after dehydration, with twin boundaries at the interface between the two variants. As the temperature was increased, crystal growth occurred. At 800 degrees C, the majority...

  4. Estimating the dopant distribution in Ca-doped alpha-SiAlON: statistical HAADF-STEM analysis and large-scale atomic modeling

    Sakaguchi, Norihito; Yamaki, Fuuta; Saito, Genki; Kunisada, Yuji
    We investigated the dopant distribution in Ca-doped alpha-SiAlON by using high-angle annular dark-field scanning transmission electron microscopy and a multi-slice image simulation. Our results showed that the electron wave propagated by hopping to adjacent Si(Al) and N(O) columns. The image intensities of the Ca columns had wider dispersions than other columns. To estimate the Ca distribution in the bulk material, we performed a Monte Carlo atomic simulation of the alpha-SiAlON with Ca dopants. A model including a short-range Coulomb-like repulsive force between adjacent Ca atoms reproduced the dispersion of the intensity distribution of the Ca column in the experimental image.

  5. Estimating the dopant distribution in Ca-doped alpha-SiAlON: statistical HAADF-STEM analysis and large-scale atomic modeling

    Sakaguchi, Norihito; Yamaki, Fuuta; Saito, Genki; Kunisada, Yuji
    We investigated the dopant distribution in Ca-doped alpha-SiAlON by using high-angle annular dark-field scanning transmission electron microscopy and a multi-slice image simulation. Our results showed that the electron wave propagated by hopping to adjacent Si(Al) and N(O) columns. The image intensities of the Ca columns had wider dispersions than other columns. To estimate the Ca distribution in the bulk material, we performed a Monte Carlo atomic simulation of the alpha-SiAlON with Ca dopants. A model including a short-range Coulomb-like repulsive force between adjacent Ca atoms reproduced the dispersion of the intensity distribution of the Ca column in the experimental image.

  6. Improving the measurement of dielectric function by TEM-EELS: avoiding the retardation effect

    Sakaguchi, Norihito; Tanda, Luka; Kunisada, Yuji
    We investigated an improved Kramers-Kronig analysis (KKA) routine for measuring the dielectric function of alpha-Al2O3, avoiding the retardation effect arising in electron energy-loss spectroscopy (EELS). The EELS data differed from the optical data in the energy range of 10-20 eV due to the retardation effect, even though Cerenkov loss was thoroughly suppressed. The calculated differential cross-section indicates that the influence of the retardation appears at scattering angles less than 0.2 mrad in the loss energy range of 10-15 eV. Using the improved KKA routine, we obtained the correct dielectric function that agreed with the optical data. The present technique is...

  7. Improving the measurement of dielectric function by TEM-EELS: avoiding the retardation effect

    Sakaguchi, Norihito; Tanda, Luka; Kunisada, Yuji
    We investigated an improved Kramers-Kronig analysis (KKA) routine for measuring the dielectric function of alpha-Al2O3, avoiding the retardation effect arising in electron energy-loss spectroscopy (EELS). The EELS data differed from the optical data in the energy range of 10-20 eV due to the retardation effect, even though Cerenkov loss was thoroughly suppressed. The calculated differential cross-section indicates that the influence of the retardation appears at scattering angles less than 0.2 mrad in the loss energy range of 10-15 eV. Using the improved KKA routine, we obtained the correct dielectric function that agreed with the optical data. The present technique is...

  8. Cotton derived porous carbon via an MgO template method for high performance lithium ion battery anodes

    Zhu, Chunyu; Akiyama, Tomohiro
    Porous carbon has received great attention for electrochemical energy storage devices. In this study, we proposed a novel and scalable method to fabricate porous carbon, which contained macro and mesopores, from sustainable biomass raw material of cotton cellulose. A MgO template, which acted as a pore creator, was incorporated into the cellulose-derived carbon by absorbing a Mg(NO3)(2) solution into cellulose fibers with subsequent drying and carbonization processes. After removing the MgO template by acid leaching, porous carbon was produced with a specific surface area as high as 1260 m(2) g(-1). The sample showed attractive electrochemical performances as the anode material...

  9. Effect of SiC Addition on Oxidation Behavior of ZrB2 at 1273 K and 1473 K

    Zhang, Lihua; Kurokawa, Kazuya
    The oxidation behavior of ZrB2-SiC composites with different contents of SiC addition was investigated at 1273 and 1473 K in air for 12 h in this study. The SiC addition contents ranged from 0 to 30 wt%. The results showed that when ZrB2-SiC composites were oxidized at 1273 K in air, a two-oxide layer-structure forms: a continuous glassy layer and a ZrO2 layer contained unoxidized SiC. When SiC content is 5 and 10 wt%, the glassy layer is mainly composed by B2O3. When SiC content is 20 and 30 wt%, a borosilicate glass could be formed on the top layer,...

  10. MnO nanocrystals incorporated in a N-containing carbon matrix for Li ion battery anodes

    Zhu, Chunyu; Han, Cheng-gong; Saito, Genki; Akiyama, Tomohiro
    In this study, MnO nanocrystals incorporated in a N-containing carbon matrix were fabricated by the facile thermal decomposition of manganese nitrate-glycine gels. MnO/C composites with different carbon contents were prepared by controlling the initial ratio of manganese to glycine. The composition, phase structure and morphology of the composites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning and transmission electron microscopy, and thermogravimetric analysis. The results indicated that MnO nanocrystals were uniformly embedded in the N-doped carbon matrix. The carbon matrix could effectively enhance the electrical conductivity of MnO and alleviate the strain arising from the discharge/charge cycling....

  11. Hindered rotational physisorption states of H-2 on Ag(111) surfaces

    Kunisada, Y.; Kasai, H.
    We have investigated the physisorption states of H-2 on Ag(111) surfaces. To clarify the accurate adsorption properties of H-2 on Ag(111), we performed first-principles calculations based on spin-polarized density functional theory (DFT) with the semiempirical DFT-D2 method and the newly-developed exchange functional with the non-local correlation functional vdW-DF2 (rev-vdW-DF2). We constructed exhaustive potential energy surfaces, and revealed that non-negligible out-of-plane potential anisotropy with a perpendicular orientation preference exists even for H-2 physisorption on planar Ag(111), as predicted by previous results of resonance-enhanced multiphoton ionization spectroscopy and temperature-programmed desorption experiments. Therefore, the molecular rotational ground states of ortho-H-2 split into two...

  12. Generation of solution plasma over a large electrode surface area

    Saito, Genki; Nakasugi, Yuki; Akiyama, Tomohiro
    Solution plasma has been used in a variety of fields such as nanomaterials synthesis, the degradation of harmful substances, and solution analysis. However, as existing methods are ineffective in generating plasma over a large surface area, this study investigated the contact glow discharge electrolysis, in which the plasma was generated on the electrode surface. To clarify the condition of plasma generation, the effect of electrolyte concentration and temperature on plasma formation was studied. The electrical energy needed for plasma generation is higher than that needed to sustain a plasma, and when the electrolyte temperature was increased from 32 to 90...

  13. Controlled synthesis of LiNi0.5Mn1.5O4 cathode materials with superior electrochemical performance through urea-based solution combustion synthesis

    Zhu, Chunyu; Han, Cheng-gong; Akiyama, Tomohiro
    High-voltage LiNi0.5Mn1.5O4 cathode materials were synthesized using urea-based solution combustion synthesis combined with a calcination treatment. The morphology and particle size distribution of the products were considerably dependent on the amount of urea fuel. The electrochemical characterization illustrated that the sample that was produced with a fuel ratio of phi = 0.5 had a homogenous particle size distribution of approximately 8 mu m, and showed the best cycling and rate performance. LiNi0.5Mn1.5O4 with two different structures of disordered Fd (3) over barm and ordered P4(3)32 were obtained by controlling the calcination process. The samples, which were calcined at 800 degrees...

  14. Solution plasma synthesis of Si nanoparticles

    Saito, Genki; Sakaguchi, Norihito
    Silicon nanoparticles (Si-NPs) were directly synthesized from a Si bar electrode via a solution plasma. In order to produce smaller Si-NPs, the effects of different electrolytes and applied voltages on the product were investigated in the experiments detailed in this paper. The results demonstrated that the use of an acidic solution of 0.1 M HCl or HNO3 produced Si-NPs without SiO2 formation. According to the transmission electron microscopy and electron energy-loss spectroscopy, the obtained Si-NPs contained both amorphous and polycrystalline Si particles, among which the smaller Si-NPs tended to be amorphous. When an alkaline solution of K2CO3 was used instead,...

  15. A pathway of nanocrystallite fabrication by photo-assisted growth in pure water

    Jeem, Melbert; bin Julaihi, Muhammad Rafiq Mirza; Ishioka, Junya; Yatsu, Shigeo; Okamoto, Kazumasa; Shibayama, Tamaki; Iwasaki, Tomio; Kato, Takahiko; Watanabe, Seiichi
    We report a new production pathway for a variety of metal oxide nanocrystallites via submerged illumination in water: submerged photosynthesis of crystallites (SPSC). Similar to the growth of green plants by photosynthesis, nanocrystallites shaped as nanoflowers and nanorods are hereby shown to grow at the protruded surfaces via illumination in pure, neutral water. The process is photocatalytic, accompanied with hydroxyl radical generation via water splitting; hydrogen gas is generated in some cases, which indicates potential for application in green technologies. Together with the aid of ab initio calculation, it turns out that the nanobumped surface, as well as aqueous ambience...

  16. Synthesis of stainless steel nanoballs via submerged glow-discharge plasma and its photocatalytic performance in methylene blue decomposition

    bin Julaihi, Muhammad Rafiq Mirza; Yatsu, Shigeo; Jeem, Melbert; Watanabe, Seiichi
    Stainless steel nanoparticles or 'nanoballs' have been synthesised using submerged glow-discharge plasma. Transmission electron microscopy showed that the nanoballs are uniformly spherical and size distribution estimation showed that their diameters are below 200nm. The decomposition of methylene blue solution under ultraviolet light with the wavelength of 354nm was observed in the presence of stainless steel nanoballs. A mixture of stainless steel nanoballs and 0.1% methylene blue dye was irradiated with ultraviolet light. The concentration of methylene blue was reduced to baseline level in 72hours. This shows that the stainless steel nanoballs have photocatalytic ability. In stainless steel nanoballs, methylene blue...

  17. Anisotropic surroundings effects on photo absorption of partially embedded Au nanospheroids in silica glass substrate

    Meng, Xuan; Shibayama, Tamaki; Yu, Ruixuan; Ishioka, Junya; Watanabe, Seiichi
    The influence of a directly adjacent or an anisotropic surrounding medium alters the plasmonic properties of a nanoparticle because it provides a mechanism for symmetry breaking of the scattering. Given the success of ion irradiation induced embedment of rigid metallic nanospheroids into amorphous substrate, it is possible to examine the effect of the silica glass substrate on the plasmonic properties of these embedded nanospheroids. In this work presented here, discrete dipole approximation (DDA) calculations for the Au nanospheroids' optical properties were performed based on 3-dimensional (3D) configuration extracted from planar SEM micrographs and cross-sectional TEM micrographs of the Au nanospheroids...

  18. A facile solution combustion synthesis of nanosized amorphous iron oxide incorporated in a carbon matrix for use as a high-performance lithium ion battery anode material

    Zhu, Chunyu; Saito, Genki; Akiyama, Tomohiro
    An amorphous iron oxide-carbon composite has been fabricated through an effective, inexpensive, and scalable method employing solution combustion synthesis. Amorphous iron oxide nanoparticles with diameters of about 5 nm were synthesized and uniformly embedded in a dense carbon matrix. The synthesized composite exhibits enhanced cyclability and rate capability, showing a high reversible capacity of 687 mA h g(1) after 200 discharge/charge cycles at a current rate of 0.5 A g (1), compared to the 400 mA h g (1) observed for Fe2O3 nanoparticles. This enhanced performance was retained despite more demanding conditions, delivering a high capacity of about 525 mA...

  19. Microencapsulation of Metal-based Phase Change Material for High-temperature Thermal Energy Storage

    Nomura, Takahiro; Zhu, Chunyu; Sheng, Nan; Saito, Genki; Akiyama, Tomohiro
    Latent heat storage using alloys as phase change materials (PCMs) is an attractive option for high-temperature thermal energy storage. Encapsulation of these PCMs is essential for their successful use. However, so far, technology for producing microencapsulated PCMs (MEPCMs) that can be used above 500 degrees C has not been established. Therefore, in this study, we developed Al-Si alloy microsphere MEPCMs covered by alpha-Al2O3 shells. The MEPCM was prepared in two steps: (1) the formation of an AlOOH shell on the PCM particles using a boehmite treatment, and (2) heat-oxidation treatment in an O-2 atmosphere to form a stable alpha-Al2O3 shell....

  20. Nanopatterns induced by pulsed laser irradiation on the surface of an Fe-Al alloy and their magnetic properties

    Yoshida, Yutaka; Oosawa, Kazuya; Watanabe, Seiichi; Kaiju, Hideo; Kondo, Kenji; Ishibashi, Akira; Yoshimi, Kyosuke
    We have studied nanopatterns induced by nanosecond pulsed laser irradiation on (111) plane surfaces of a polycrystalline iron-aluminum alloy and evaluated their magnetic properties. Multiple nanosecond pulsed laser irradiation induces a wavelength-dependent surface transformation of the lattice structure from a B2-type to a supersaturated body centered cubic lattice. The selective formation of surface nanopatterns consisting of holes, stripes, polygonal networks, and dot-like nanoprotrusions can be observed. Furthermore, focused magneto-optical Kerr effect measurements reveal that the magnetic properties of the resultant nanostructured region changes from a paramagnetic to a ferromagnetic phase in accordance with the number of laser pulses.

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