Publications by authors named "Norihito Sakaguchi"

29 Publications

  • Page 1 of 1

Bulk tungsten-substituted vanadium oxide for low-temperature NOx removal in the presence of water.

Nat Commun 2021 Jan 25;12(1):557. Epub 2021 Jan 25.

Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University Hachioji, Tokyo, 192-0397, Japan.

NH-SCR (selective catalytic reduction) is important process for removal of NOx. However, water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH-SCR at a low temperature (100-150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W-substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5-20 vol% water) NO conversion at 150 °C (250 ppm NO, 250 ppm NH, 4% O, SV = 40000 mL h g). Lewis acid sites of W-substituted vanadium oxide are converted to Brønsted acid sites under a wet condition while the distribution of Brønsted and Lewis acid sites does not change without tungsten. NH species adsorbed on Brønsted acid sites react with NO accompanied by the reduction of V sites at 150 °C. The high redox ability and reactivity of Brønsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor.
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http://dx.doi.org/10.1038/s41467-020-20867-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7835234PMC
January 2021

Effect of conditioning and 1 year aging on the bond strength and interfacial morphology of glass-ionomer cement bonded to dentin.

Dent Mater 2021 Jan 21;37(1):106-112. Epub 2020 Nov 21.

Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom. Electronic address:

Objective: The purpose of this study was to determine the bond stability and the change in interfacial ultra-structure of a conventional glass-ionomer cement bonded to dentin, with and without pre-treatment using a polyalkenoic acid conditioner.

Methods: The occlusal dentin surfaces of six teeth were ground flat. Glass-ionomer cement was bonded to the surfaces either with or without polyalkenoic acid conditioning. The teeth were sectioned into 1-mm stick-shaped specimens. The specimens obtained were randomly assigned to two groups with different periods of storage in water: 1 week and 1 year. The micro-tensile bond strength (μTBS) was determined for each storage time. Additional specimens were prepared for Transmission Electron Microscopy (TEM); they were produced with or without prior polyalkenoic acid conditioning in the same way as in the μTBS test.

Results: There was no significant difference in μTBS to conditioned dentin and non-conditioned dentin (p > 0.05). The failures appeared to be of a mixed nature, although aging caused more areas of cohesive than adhesive failure in both groups. The TEM observation showed an intermediate layer, a matrix-rich layer and a partially demineralized layer in the polyalkenoic acid conditioned group.

Significance: Aging did not reduce the bond strength of the conventional glass-ionomer cement to dentin with or without the use of a polyalkenoic acid conditioner.
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http://dx.doi.org/10.1016/j.dental.2020.10.016DOI Listing
January 2021

Exploration of Long-Life Pt/Heteroatom-Doped Graphene Catalysts in Hydrogen Atmosphere.

ACS Omega 2019 Apr 10;4(4):6573-6584. Epub 2019 Apr 10.

Center for Advanced Research of Energy and Materials, Hokkaido University, Kita 13 Nishi 8, Kitaku, Sapporo 060-8628, Japan.

We investigated the H and H adsorption effects on the stability of a Pt atom on various heteroatom-doped graphene supports using first-principles calculations based on density functional theory. We show that H and H adsorptions on the Pt atom weaken the interaction between the Pt atom and graphene support and decrease the adsorption energy of Pt atoms. H adsorption on Pt atoms decreases the adsorption energy of Pt atoms on all graphene supports by more than 30%, whereas H adsorption only affects pristine, O-, and S-doped graphene. These results indicate that the hydrogen atmosphere enhances the detachment of Pt catalysts. However, the B-, O-, Si-, P-doped, and monovacant graphene still maintained large adsorption energies of PtH and PtH of more than 1.5 eV. In addition, the diffusion barriers of PtH and PtH on pristine graphene were calculated to be less than 0.07 eV, which further demonstrated that H and H enhance the degradation of Pt catalysts. Even after H and H adsorptions on a Pt atom, O-, Si-, P-doped, and monovacant graphene still maintained large diffusion barriers of more than 1 eV. Therefore, we concluded that O-, Si-, and P-doped graphene are suitable supports for Pt catalysts in a hydrogen atmosphere.
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http://dx.doi.org/10.1021/acsomega.9b00750DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648745PMC
April 2019

Hydrogen Isotope Absorption in Unary Oxides and Nitrides with Anion Vacancies and Substitution.

Chemphyschem 2019 05 14;20(10):1369-1375. Epub 2019 Feb 14.

Center for Advanced Research of Energy and Materials, Hokkaido University, Kita 13 Nishi 8, Kitaku, Sapporo, 060-8628, Japan.

The absorption states of hydrogen isotopes in various ceramic materials were investigated by density functional theory. For pristine ceramic materials, main-group oxides do not form any bond with a hydrogen atom. However, transition metal oxides form hydroxyl groups and absorb hydrogen atoms. Main-group and transition metal nitrides form ionic bonds between a hydrogen atom and the surrounded cation. For anion-deficient ceramic materials, hydrogen atoms are negatively charged because of excess electrons induced by anion vacancies, and ionic bonds form with the surrounded cation, which stabilizes the hydrogen absorption state. N substitutional doping into oxides introduces an electron hole, while O substitutional doping into the nitrides introduces an excess of electrons. Therefore, hydrogen isotopes form covalent bonds in N-substituted oxides, and form hydride ions in O-substituted nitrides. Thus, Al O , SiO , CrN, and TiN are promising materials as hydrogen permeation barriers.
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http://dx.doi.org/10.1002/cphc.201801091DOI Listing
May 2019

Solution-Plasma-Mediated Synthesis of Si Nanoparticles for Anode Material of Lithium-Ion Batteries.

Nanomaterials (Basel) 2018 Apr 27;8(5). Epub 2018 Apr 27.

Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kitaku, Sapporo 060-8628, Japan.

Silicon anodes have attracted considerable attention for their use in lithium-ion batteries because of their extremely high theoretical capacity; however, they are prone to extensive volume expansion during lithiation, which causes disintegration and poor cycling stability. In this article, we use two approaches to address this issue, by reducing the size of the Si particles to nanoscale and incorporating them into a carbon composite to help modulate the volume expansion problems. We improve our previous work on the solution-plasma-mediated synthesis of Si nanoparticles (NPs) by adjusting the electrolyte medium to mild buffer solutions rather than strong acids, successfully generating Si-NPs with <10 nm diameters. We then combined these Si-NPs with carbon using MgO-template-assisted sol-gel combustion synthesis, which afforded porous carbon composite materials. Among the preparations, the composite material obtained from the LiCl 0.2 M + H₃BO₃ 0.15 M solution-based Si-NPs exhibited a high reversible capacity of 537 mAh/g after 30 discharge/charge cycles at a current rate of 0.5 A/g. We attribute this increased reversible capacity to the decreased particle size of the Si-NPs. These results clearly show the applicability of this facile and environmentally friendly solution-plasma technique for producing Si-NPs as an anode material for lithium-ion batteries.
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http://dx.doi.org/10.3390/nano8050286DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5977300PMC
April 2018

Carbon Monoxide Oxidation by Polyoxometalate-Supported Gold Nanoparticulate Catalysts: Activity, Stability, and Temperature- Dependent Activation Properties.

Angew Chem Int Ed Engl 2018 02 15;57(6):1523-1527. Epub 2018 Jan 15.

Research Center for Gold Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, 192-0397, Japan.

Nanoparticulate gold supported on a Keggin-type polyoxometalate (POM), Cs [α-SiW O ]⋅n H O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was -67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U-shaped curve. It was revealed by IR measurement that Au was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas-phase reactions.
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http://dx.doi.org/10.1002/anie.201710424DOI Listing
February 2018

Three-dimensional analysis of Eu dopant atoms in Ca-α-SiAlON via through-focus HAADF-STEM imaging.

Ultramicroscopy 2017 04 31;175:97-104. Epub 2017 Jan 31.

Center for Advanced Research of Energy and Materials, Hokkaido University, Kita 13 Nishi 8, Kitaku, Sapporo 060-8628, Japan.

Three-dimensional (3D) distributional analysis of individual dopant atoms in materials is important to development of optical, electronic, and magnetic materials. In this study, we adopted through-focus high-angle annular dark-field (HAADF) imaging for 3D distributional analysis of Eu dopant atoms in Ca-α-SiAlON phosphors. In this context, the effects of convergence semi-angle and Eu z-position on the HAADF image contrast were investigated. Multi-slice image simulation revealed that the contrast of the dopant site was sensitive to change of the defocus level. When the defocus level matched the depth position of a Eu atom, the contrast intensity was significantly increased. The large convergence semi-angle greatly increased the depth resolution because the electron beam tends spread instead of channeling along the atomic columns. Through-focus HAADF-STEM imaging was used to analyze the Eu atom distribution surrounding 10nm cubes with defocus steps of 0.68nm each. The contrast depth profile recorded with a narrow step width clearly analyzed the possible depth positions of Eu atoms. The radial distribution function obtained for the Eu dopants was analyzed using an atomic distribution model that was based on the assumption of random distribution. The result suggested that the Ca concentration did not affect the Eu distribution. The decreased fraction of neighboring Eu atoms along z-direction might be caused by the enhanced short-range Coulomb-like repulsive forces along the z-direction.
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http://dx.doi.org/10.1016/j.ultramic.2017.01.014DOI Listing
April 2017

Synthesis of ε-Keggin-Type Cobaltomolybdate-Based 3D Framework Material and Characterization Using Atomic-Scale HAADF-STEM and XANES.

Inorg Chem 2017 Feb 9;56(4):2042-2049. Epub 2017 Feb 9.

Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University , 1-4-1 Kagamiyama, Higashi Hiroshima 739-8527, Japan.

We describe the preparation of ε-Keggin-type cobaltomolybdate-based 3D frameworks with sodium cations, NaH[ε-CoMoMoOCo], and their characterization by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) spectroscopy. Atomic-scale HAADF-STEM images of ε-Keggin compounds were obtained for the first time, and positions of Mo and Co were confirmed. Furthermore, clear evidence of the presence of a CoO tetrahedron was obtained by X-ray absorption near-edge structure (XANES) analysis. Their characterization clearly revealed that ε-Keggin-type cobaltomolybdate units, [ε-CoMoO], constructed by a central CoO tetrahedron and 12 surrounding MoO octahedra, are linked with Co to form 3D frameworks.
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http://dx.doi.org/10.1021/acs.inorgchem.6b02748DOI Listing
February 2017

Measurement of the dielectric function of α-Al2O3 by transmission electron microscopy - Electron energy-loss spectroscopy without Cerenkov radiation effects.

Ultramicroscopy 2016 10 6;169:37-43. Epub 2016 Jul 6.

Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.

The dielectric function of α-Al2O3 was measured by electron energy-loss spectroscopy (EELS) coupled with the difference method. The influence of Cerenkov radiation was significant in measurements using a 200kV transmission electron microscope (TEM) and the correct dielectric function could not be obtained using the conventional EELS procedure. However, a good agreement between the optical data and EELS for the dielectric functions was obtained via a 60kV TEM. Combining EELS and the difference method, however, provided an accurate measurement of the dielectric function for α-Al2O3 even at an accelerating voltage of 200kV. The combination of EELS and the difference method in the nano-beam diffraction mode could derive an accurate dielectric function with superior spatial resolution regardless of the occurrence of Cerenkov radiation.
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http://dx.doi.org/10.1016/j.ultramic.2016.07.003DOI Listing
October 2016

Carbon nanohorns allow acceleration of osteoblast differentiation via macrophage activation.

Nanoscale 2016 Aug 14;8(30):14514-22. Epub 2016 Jul 14.

Department of Oral Functional Prosthodontics, Division of Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan.

Carbon nanohorns (CNHs), formed by a rolled graphene structure and terminating in a cone, are promising nanomaterials for the development of a variety of biological applications. Here we demonstrate that alkaline phosphatase activity is dramatically increased by coculture of human monocyte derived macrophages (hMDMs) and human mesenchymal stem cells (hMSCs) in the presence of CNHs. CNHs were mainly localized in the lysosome of macrophages more than in hMSCs during coculturing. At the same time, the amount of Oncostatin M (OSM) in the supernatant was also increased during incubation with CNHs. Oncostatin M (OSM) from activated macrophage has been reported to induce osteoblast differentiation and matrix mineralization through STAT3. These results suggest that the macrophages engulfed CNHs and accelerated the differentiation of mesenchymal stem cells into the osteoblast via OSM release. We expect that the proof-of-concept on the osteoblast differentiation capacity by CNHs will allow future studies focused on CNHs as ideal therapeutic materials for bone regeneration.
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http://dx.doi.org/10.1039/c6nr02756cDOI Listing
August 2016

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

Microscopy (Oxf) 2016 10 6;65(5):415-421. Epub 2016 Jul 6.

Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.

We investigated an improved Kramers-Kronig analysis (KKA) routine for measuring the dielectric function of α-AlO, 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 especially useful in measuring the dielectric function by EELS with a small collection semi-angle.
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http://dx.doi.org/10.1093/jmicro/dfw023DOI Listing
October 2016

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

Microscopy (Oxf) 2016 10 21;65(5):400-406. Epub 2016 Jun 21.

Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.

We investigated the dopant distribution in Ca-doped α-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 α-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.
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http://dx.doi.org/10.1093/jmicro/dfw020DOI Listing
October 2016

Ultrathin inorganic molecular nanowire based on polyoxometalates.

Nat Commun 2015 Jul 3;6:7731. Epub 2015 Jul 3.

Catalysis Research Center, Hokkaido University, N-21, W-10, Kita-ku, Sapporo 001-0021, Japan.

The development of metal oxide-based molecular wires is important for fundamental research and potential practical applications. However, examples of these materials are rare. Here we report an all-inorganic transition metal oxide molecular wire prepared by disassembly of larger crystals. The wires are comprised of molybdenum(VI) with either tellurium(IV) or selenium(IV): {(NH4)2[XMo6O21]}n (X=tellurium(IV) or selenium(IV)). The ultrathin molecular nanowires with widths of 1.2 nm grow to micrometre-scale crystals and are characterized by single-crystal X-ray analysis, Rietveld analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, thermal analysis and elemental analysis. The crystals can be disassembled into individual molecular wires through cation exchange and subsequent ultrasound treatment, as visualized by atomic force microscopy and transmission electron microscopy. The ultrathin molecular wire-based material exhibits high activity as an acid catalyst, and the band gap of the molecular wire-based crystal is tunable by heat treatment.
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http://dx.doi.org/10.1038/ncomms8731DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506542PMC
July 2015

Solution plasma synthesis of Si nanoparticles.

Nanotechnology 2015 Jun 20;26(23):235602. Epub 2015 May 20.

Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo 060-8628, Japan.

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, amorphous SiO2 particles were synthesized owing to the corrosion of Si in the high-temperature environment. The pH values of KCl and KNO3 increased during electrolysis, and the products were partially oxidized in the alkaline solutions. The particle size increased with an increasing applied voltage because the excitation temperature of the plasma increased.
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http://dx.doi.org/10.1088/0957-4484/26/23/235602DOI Listing
June 2015

DNA/Ag Nanoparticles as Antibacterial Agents against Gram-Negative Bacteria.

Nanomaterials (Basel) 2015 Mar 3;5(1):284-297. Epub 2015 Mar 3.

Graduate School of Environmental Science, Hokkaido University, Hokkaido 060-0810, Japan.

Silver (Ag) nanoparticles were produced using DNA extracted from salmon milt as templates. Particles spherical in shape with an average diameter smaller than 10 nm were obtained. The nanoparticles consisted of Ag as the core with an outermost thin layer of DNA. The DNA/Ag hybrid nanoparticles were immobilized over the surface of cotton based fabrics and their antibacterial efficiency was evaluated using as the typical Gram-negative bacteria. The antibacterial experiments were performed according to the Antibacterial Standard of Japanese Association for the Functional Evaluation of Textiles. The fabrics modified with DNA/Ag nanoparticles showed a high enough inhibitory and killing efficiency against at a concentration of Ag ≥ 10 ppm.
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http://dx.doi.org/10.3390/nano5010284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312851PMC
March 2015

Laser-assisted sample preparation of silicon for high-resolution transmission electron microscopy.

Microscopy (Oxf) 2015 Apr 3;64(2):111-9. Epub 2015 Jan 3.

Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.

A sample-polishing technique was developed to provide a well-defined thin foil of Si with a clean surface down to atomic dimensions. The resulting samples permit high-resolution transmission electron microscope (HRTEM) imaging unobstructed by artifacts originating from a damaged sample. Samples were not polished by dynamic momentum transfer via accelerated ions like in ion milling; instead, valence electron excitation by photon absorption was used. HRTEM inspection showed that the foils prepared by this method were free from extrinsic lattice defects and had smooth surfaces down to atomic dimensions.
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http://dx.doi.org/10.1093/jmicro/dfu114DOI Listing
April 2015

Ultra-high density single nanometer-scale anodic alumina nanofibers fabricated by pyrophosphoric acid anodizing.

Sci Rep 2014 Dec 10;4:7411. Epub 2014 Dec 10.

Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, N13-W8, Kita-ku, Sapporo, Hokkaido, 060-8628, Japan.

Anodic oxide fabricated by anodizing has been widely used for nanostructural engineering, but the nanomorphology is limited to only two oxides: anodic barrier and porous oxides. Therefore, the discovery of an additional anodic oxide with a unique nanofeature would expand the applicability of anodizing. Here we demonstrate the fabrication of a third-generation anodic oxide, specifically, anodic alumina nanofibers, by anodizing in a new electrolyte, pyrophosphoric acid. Ultra-high density single nanometer-scale anodic alumina nanofibers (10(10) nanofibers/cm(2)) consisting of an amorphous, pure aluminum oxide were successfully fabricated via pyrophosphoric acid anodizing. The nanomorphologies of the anodic nanofibers can be controlled by the electrochemical conditions. Anodic tungsten oxide nanofibers can also be fabricated by pyrophosphoric acid anodizing. The aluminum surface covered by the anodic alumina nanofibers exhibited ultra-fast superhydrophilic behavior, with a contact angle of less than 1°, within 1 second. Such ultra-narrow nanofibers can be used for various nanoapplications including catalysts, wettability control, and electronic devices.
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http://dx.doi.org/10.1038/srep07411DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4261161PMC
December 2014

Stability of {111}Pd/{0002}ZnO polar interface formed by internal oxidation of Pd-Zn alloys.

Microscopy (Oxf) 2014 Dec 20;63(6):463-7. Epub 2014 Oct 20.

Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan

We investigated the stability of Pd/ZnO polar interfaces formed by internal oxidation of Pd-Zn alloys by using high-resolution transmission electron microscopy, electron energy-loss spectroscopy and convergent-beam electron diffraction. At 1273 K, a [Formula: see text] polar interface defaceted and transformed into a curved interface, while another (111)Pd/(0002)ZnO polar interface retained its flatness. The [Formula: see text] polar interface lost some stability over non-polar interfaces at 1273 K, while the (111)Pd/(0002)ZnO polar interface remained stable.
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http://dx.doi.org/10.1093/jmicro/dfu095DOI Listing
December 2014

Preparation, structural characterization, and ion-exchange properties of two new zeolite-like 3D frameworks constructed by ε-Keggin-type polyoxometalates with binding metal ions, H11.4[ZnMo12O40Zn2]1.5- and H7.5[Mn0.2Mo12O40Mn2]2.1-.

Inorg Chem 2014 Jul 9;53(14):7309-18. Epub 2014 Jul 9.

Catalysis Research Center, Hokkaido University , N-21, W-10 Kita-ku, Sapporo 001-0021, Japan.

Two new ε-Keggin-type polyoxometalate-based 3D frameworks, Na1.5H11.4[ε-Zn(II)Mo(V)10.9Mo(VI)1.1O40{Zn(II)}2] and (NH4)2.1H7.5[ε-Mn(II)0.2Mo(V)6Mo(VI)6O40{Mn(II)}2], are prepared, and their structures are determined by powder X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and elemental analysis. ε-Keggin-type polyoxomolybdate units, [ε-ZnMo12O40] and [ε-Mn0.2Mo12O40], are linked with Zn(2+) and Mn(2+), respectively, in a tetrahedral fashion to form 3D frameworks. They show zeolite-like ion-exchange properties and redox properties. The ε-Keggin-based 3D framework shows high chemical composition diversity and can incorporate different elements in the framework.
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http://dx.doi.org/10.1021/ic500630hDOI Listing
July 2014

Tetrahedral connection of ε-Keggin-type polyoxometalates to form an all-inorganic octahedral molecular sieve with an intrinsic 3D pore system.

Inorg Chem 2014 Jan 30;53(2):903-11. Epub 2013 Dec 30.

Catalysis Research Center, Hokkaido University , N-21, W-10, Kita-ku, Sapporo 001-0021, Japan.

A new type of polyoxometalate-based porous material was successfully synthesized. The new material is the first fully inorganic Keggin-type polyoxometalate-based microporous material with intrinsically ordered open micropores and is the third member of the small family of octahedral molecular sieves (OMSs). Twelve MoO6 or VO6 octahedra surround a central VO4 tetrahedron to form ε-Keggin polyoxometalate building blocks (ε-VMo9.4V2.6O40) that are linked by Bi(III) ions to form crystalline Mo-V-Bi oxide with a diamondoid topology. The presence of a tetrahedral shape of the ε-Keggin polyoxometalate building block results in arrangement of microporosity in a tetrahedral fashion which is new in OMSs. Owing to its microporosity, this Mo-V-Bi oxide shows zeolitic-like properties such as ion-exchange and molecule adsorption.
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http://dx.doi.org/10.1021/ic4022849DOI Listing
January 2014

Dislocation loop formation and growth under in situ laser and/or electron irradiation.

Sci Rep 2011 12;1:190. Epub 2011 Dec 12.

Centre for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, N13, W8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.

Vacancies and interstitial atoms are primary lattice (point) defects that cause observable microstructural changes, such as the formation of dislocation loops and voids in crystalline solids. These defects' diffusion properties determine the phase stability and environmental resistibility of macroscopic materials under ambient conditions. Although in situ methods have been proposed for measuring the diffusion energy of point defects, direct measurement has been limited. In this study, we propose an alternative in situ method to measure the activation energy for vacancy migration under laser irradiation using a pulsed laser beam from a laser-equipped high-voltage electron microscope (laser-HVEM). We made in situ observations that revealed the formation and growth of vacancy dislocation loops in an austenitic stainless steel during laser irradiation. These loops continued to grow when thermal annealing was performed after laser irradiation at the same temperature. We anticipate that laser-HVEM will provide a new method for investigating lattice defects.
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http://dx.doi.org/10.1038/srep00190DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3240952PMC
September 2013

Enhanced capacitance of composite anodic ZrO₂ films comprising high permittivity oxide nanocrystals and highly resistive amorphous oxide matrix.

ACS Appl Mater Interfaces 2011 Jul 20;3(7):2665-70. Epub 2011 Jun 20.

Division of Materials Chemistry, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.

Anodic oxide films with nanocrystalline tetragonal ZrO(2) precipitated in an amorphous oxide matrix were formed on Zr-Si and Zr-Al alloys and had significantly enhanced capacitance in comparison with those formed on zirconium metal. The capacitance enhancement was associated with the formation of a high-temperature stable tetragonal ZrO(2) phase with high relative permittivity as well as increased ionic resistivity, which reduces the thickness of anodic oxide films at a certain formation voltage. However, there is a general empirical trend that single-phase materials with higher permittivity have lower ionic resistivity. This study presents a novel material design based on a nanocrystalline-amorphous composite anodic oxide film for capacitor applications.
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http://dx.doi.org/10.1021/am200460cDOI Listing
July 2011

Transmission electron microscopic observation of cells cultured on multiwalled carbon nanotube-coated sponges.

J Electron Microsc (Tokyo) 2010 23;59(5):447-50. Epub 2010 Jun 23.

The cell structure and interface between cultured cells and a multiwalled carbon nanotube (MWCNT)-coated sponge (MWCNT-coated sponge) were observed by transmission electron microscopy (TEM). Moreover, the atomic structure of MWCNTs that entered the cells was also examined by means of high-resolution TEM (HRTEM). MWCNTs were observed in the cytoplasm, and a few MWCNTs were recognized in the cell nuclei. Those MWCNTs maintained their structure there. Subcellular organelles did not appear to be different from those on the collagen sponge despite the cellular uptake of MWCNTs.
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http://dx.doi.org/10.1093/jmicro/dfq051DOI Listing
February 2011

Low-voltage and high-voltage TEM observations on MWCNTs of rat in vivo.

Biomed Mater Eng 2009 ;19(2-3):93-9

Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo, Japan.

In the present study, we focused on the optimal conditions for observation of morphology and atomic structure of carbon nanotube (CNT) in vivo by transmission electron microscopy (TEM). Either low-voltage or high-voltage TEMs was chosen for the high-contrast or high-resolution imaging of subcutaneous tissue and the multi-wall CNT (MWCNT). The morphology and structure of each cell organelle were well recognized using the low-voltage TEM at 75 kV. Individual MWCNTs forming the cluster were also visible by the low-voltage TEM. On the contrary, the high-voltage TEM image at 1250 kV shows poor contrast on both the cell organelles and MWCNTs. However, graphene layers of MWCNT were clearly visible in the HRTEM image using the high-voltage TEM. The influence of the surrounding biological tissue can be disregarded by the high-energy electrons due to their weak scattering/absorption effect in the tissue. It was indicated that the usage of the high-voltage TEM is quite effective to the atomic structure analysis of nano-crystalline materials in vivo.
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http://dx.doi.org/10.3233/BME-2009-0568DOI Listing
August 2009

Synthesis of orthorhombic Mo-V-Sb oxide species by assembly of pentagonal Mo6O21 polyoxometalate building blocks.

Angew Chem Int Ed Engl 2009 ;48(21):3782-6

Catalysis Research Center, Hokkaido University, N-21, W-10, Sapporo, 001-0021, Japan.

Mix and match: The pentagonal [Mo(6)O(21)](n-) polyoxomolybdate building block assembles with other sources of Mo, V, and Sb ions to form an orthorhombic Mo-V-Sb oxide. The first single-crystal X-ray analysis of an orthorhombic Mo-V-based oxide, a promising catalyst for light alkane selective oxidation known as the "M1 phase", revealed the structure of the compound.
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http://dx.doi.org/10.1002/anie.200805792DOI Listing
June 2009

High-resolution electron microscopy of multi-wall carbon nanotubes in the subcutaneous tissue of rats.

J Electron Microsc (Tokyo) 2008 Oct;57(5):159-64

Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Kita13, Nishi7, Kita-ku, Sapporo 060-8586, Japan.

The atomic structure of multi-wall carbon nanotubes (MWCNTs) implanted in the subcutaneous tissue of rats was examined by means of high-resolution transmission electron microscopy (HRTEM). Clusters of the MWCNTs implanted in the subcutaneous tissue were well recognized by the TEM observations. It was indicated that some nanotubes were taken in phagocytes after the 1-year implantation. The deterioration of crystalline structure of the nanotubes in phagocytes was shown by the HRTEM observation. It was suggested that the deterioration of the nanotubes was due to the peeling of the outer graphene layers in the phagocytes.
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http://dx.doi.org/10.1093/jmicro/dfn016DOI Listing
October 2008

Nano-scale phase transformation in Ti-implanted austenitic 301 stainless steel.

J Electron Microsc (Tokyo) 2003 ;52(5):449-53

Center for Advanced Research of Energy Technology, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo 060-8628, Japan.

Phase-transformation behaviours were investigated for austenitic 301 stainless steel during implantation at room temperature with 300 keV Ti ions to fluences of 8 x 10(19) to approximately 3 x 10(21) ions m(-2) by means of transmission electron microscopy. The cross-sectional specimen was prepared using a focused ion beam. Plan observation of the implanted specimen showed that phase transformation from gamma-phase to alpha-phase was induced by implantation to a fluence of 3 x 10(20) Ti ions m(-2). The nucleation of the irradiation (implantation)-induced phase increased with the increase of the dose. The orientation relationship between the gamma matrix and the induced alpha martensitic phase was identified as (011)alpha//(111)gamma and [11-1]alpha//[10-1], close to the Kurdjumov-Sachs relationship. Cross-sectional observation after implantation to a fluence of 5 x 10(20) ions m(-2) showed that phase transformation mostly nucleated near the surface and occurred in the higher the concentration gradient of the implanted ion, i.e. a higher stress concentration takes place and this stress introduced by the implanted ions acts as a driving force for the transformation.
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http://dx.doi.org/10.1093/jmicro/52.5.449DOI Listing
January 2004

Radiation-induced segregation and precipitation behaviours around cascade clusters under electron irradiation.

J Electron Microsc (Tokyo) 2003 ;52(1):63-8

Center for Advanced Research of Energy Technology, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan.

We have investigated the formation of cascade clusters and structural changes in them by means of electron irradiation following ion irradiation in an austenitic stainless steel. Almost all of the cascade clusters, which were introduced by the ion irradiation, grew to form interstitial-type dislocation loops or vacancy-type stacking fault tetrahedra after electron irradiation at 623 K, whereas a few of the dot-type clusters remained in the matrix. It was possible to recognize the concentration of Ni and Si by radiation-induced segregation around the dot-type clusters. After electron irradiation at 773 K, we found that some cascade clusters became precipitates (delta-Ni2Si) due to radiation-induced precipitation. This suggests that the cascade clusters could directly become precipitation sites during irradiation.
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http://dx.doi.org/10.1093/jmicro/52.1.63DOI Listing
June 2003