Akihiko Fujiwara

Japan Synchrotron Radiation Research Institute (JASRI), Tatsuno, Hyōgo, Japan

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Publications (221)551.37 Total impact

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    ABSTRACT: The structure of high-temperature liquids is an important topic for understanding the fragility of liquids. Here we report the structure of a high-temperature non-glass-forming oxide liquid, ZrO2, at an atomistic and electronic level. The Bhatia–Thornton number–number structure factor of ZrO2 does not show a first sharp diffraction peak. The atomic structure comprises ZrO5, ZrO6 and ZrO7 polyhedra with a significant contribution of edge sharing of oxygen in addition to corner sharing. The variety of large oxygen coordination and polyhedral connections with short Zr–O bond lifetimes, induced by the relatively large ionic radius of zirconium, disturbs the evolution of intermediate-range ordering, which leads to a reduced electronic band gap and increased delocalization in the ionic Zr–O bonding. The details of the chemical bonding explain the extremely low viscosity of the liquid and the absence of a first sharp diffraction peak, and indicate that liquid ZrO2 is an extremely fragile liquid.
    Nature Communications 12/2014; 5:5892. · 10.74 Impact Factor
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    ABSTRACT: The organized structure and proton transport property in sulfonated polyimide (SPI) thin film have been studied, much less is known at the interfacial charge transport during confinement of such materials. The proton conductivity of SPI thin film is correlated well with the highly oriented polymer structures as determined by infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (p-MAIRS) and in situ RH dependent synchrotron grazing incidence X-ray diffraction (GI-XRD). The high proton conductivity of 2.8 × 10−1Scm−1 at 80°C and 90% RH was achieved in the highly oriented SPI thin film. In contrast, the bulk SPI showed the drop of conductivity value at high relative humidity region, which is due to the significant structural disorder accompanied by the strong interaction between the sulfonic acid side chains and water molecules.
    Electrochemistry -Tokyo- 10/2014; 82(10):865-869. · 0.98 Impact Factor
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    ABSTRACT: A strategy to modulate the in-plane structural arrangement in preferentially oriented crystalline metal–organic framework (MOF) nanosheets assembled by a two-dimensional interfacial reaction between porphyrin units and metal ion linkers is reported. Starting with a tetratopic porphyrin MOF nanofilm, NAFS-2, the framework size and shape are modified by employing specially designed building units, a trans-ditopic and an expanded tetratopic porphyrin, and Cu2+ linkers. Reducing the number of binding parts affords a MOF nanosheet, NAFS-31, with a distorted in-plane structure. Extension of the peripheral substituents, while maintaining the tetratopic porphyrin geometry, results in marked unit cell size enlargement in an undistorted square grid in the MOF nanofilm, NAFS-41. The exquisite geometric control that these structural modifications entail is valuable to allow switching of chemical/physical properties of the nanosheets and lead to realization of their use in nanotechnological applications.
    ChemPlusChem 07/2014; · 3.24 Impact Factor
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    ABSTRACT: Understanding the nature of superconductivity in iron-based compounds is essential in the development of new strategies to increase T c. Using a charge density analysis based on synchrotron radiation X-ray powder diffraction data, we found that the charge carriers only accumulated in the iron layer of the superconducting phase of LaFeAsO1 - x F x at low temperatures. Analysis of the electrostatic potential distribution revealed the concerted enhancement of the electronic polarization of the As ions and the carrier redistribution. This suggests that the enhanced electronic polarization of the As ion plays an important role in inducing high T c superconductivity, and that the polaron concept, which has been previously regarded as an untenable mechanism, should be reconsidered for the description of the iron-arsenide superconducting phase.
    IUCrJ. 05/2014; 1(Pt 3):155-9.
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    ABSTRACT: Electric dipole engineering is now an emerging technology for high electron-mobility transistors, ferroelectric random access memory and multiferroic devices etc. Although various studies to provide insight into dipole moment behaviour, such as phase transition, order and disorder states, have been reported, macroscopic spontaneous polarization has been mainly discussed so far. Here, visualization of the electric dipole arrangement in layered ferro-electrics Bi 2 SiO 5 by means of combined analysis of maximum entropy charge density and electrostatic potential distribution analysis based on synchrotron radiation X-ray powder diffraction data is reported. It was found that the hierarchical dipole orders, the weak-ferroelectric and ferroelectric configura-tions, were observed in the Bi 2 O 2 and the SiO 3 layers, respectively, and the ferrielectric configuration was realised by the interlayer interaction. This discovery provides a new method to visualize the local polarization in ferroelectric materials.
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    ABSTRACT: We have developed anomalous x-ray scattering (AXS) spectrometers, that employ intrinsic Ge detectors and crystal analyzers, at SPring-8. The use of LiF analyzer crystal provides us with an energy resolution of ~ 12 eV. Furthermore, it has been established that the use of AXS technique is essential to reveal the relationship between the atomic structure and its function of a fast phase-change material, Ge2Sb2Te5. We were able to address the issue of why the amorphous phase of fast phase change materials is stable at room temperature for a long time despite the fact that it can rapidly transform to the crystalline phase by using a combination of AXS and large scale density functional theory-based molecular dynamics simulations.
    Journal of Physics Conference Series 04/2014; 502(1):012014.
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    ABSTRACT: Single-crystal X-ray diffraction was employed to study the structural-electronic phase transition of IrTe$_2$ at approximately 270 K. The low-temperature structure was found to be a triclinic (space group $P\bar{1}$) characterized by the partial formation of Ir$_2$ dimers in the triangular lattice of IrTe$_2$, resulting in a structural modulation with a wave vector of ${\bf q} = (1/5, 0, -1/5)$. First-principles band calculations demonstrate that tilted two-dimensional Fermi surfaces emerge in the triclinic phase, suggesting that switching of the conducting planes occurs from the basal plane of the trigonal IrTe$_2$ to the tilted plane normal to ${\bf q}$ of the triclinic IrTe$_2$.
    Journal of the Physical Society of Japan 02/2014; 83(3). · 1.48 Impact Factor
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    ABSTRACT: Ladder systems situated in a crossover from one dimensionality to two dimensionalities have been an attractive research target, because the physical properties, which are associated with dimensionality, are strongly dependent on the number of constituent legs. However, control of the intraladder configuration and electronic properties based on the substitution of structural components remain challenging tasks in materials science. On the other hand, structural design using coordination chemistry offers crucial advantages for architectural and electronic variations through substitutions of metal-organic building blocks. Here, we show the rational design and electronic properties of novel metal complex-based two-legged ladder compounds with several organic rung units: 4,4'-bipyridine, trans-1,4-diaminocyclohexane, and 4,4'-azopyridine. Single-crystal X-ray studies show that these two-legged ladder compounds are composed of halogen-bridged mixed-valence one-dimensional chains (MX chains) as their constituent legs. Depending on the molecular shape of the organic rung units, unique configurations of two-legged ladder lattices with periodic distortion of the legs are achieved. In addition, the electronic absorption spectra show that intervalence charge-transfer (IVCT) band gap of the two-legged ladder system increases with increasing degree of distortion of the leg. We have demonstrated for the first time that a two-legged ladder system shows a unique relationship between IVCT energy and the distortion parameter of the leg, as distinct from a single MX chain system. These systematic investigations, not only of configurations based on the rung variation but also of electronic states in metal-organic ladder system, provide the possibility for wide and rational tunings of physical and electronic properties of metal complex-based functional materials.
    Inorganic Chemistry 01/2014; · 4.79 Impact Factor
  • H. Yano, M. Abe, A. Fujiwara
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    ABSTRACT: After successful rendezvous observation and landing for surface sampling from the near Earth asteroid 25148 Itokawa by the Hayabusa MUSES-C mission Japan is preparing for follow-up minor body missions in the post-Hayabusa era According to Japan s minor body exploration roadmap as well as on-going discussion within the JAXA ISAS Minor Body Exploration Working Group which is consisted of planetary scientists and astronautical engineers from all over Japan the most recommended candidate at this point is a sample return mission from known spectra NEOs with a C-type asteroid as the top priority target after Hayabusa s sample return from the S-type Itokawa in 2010 By best utilizing space technologies Hayabusa successfully demonstrated and upgrading lessons learned from the Hayabusa operation in the interplanetary space and in the vicinity of the asteroid the next minor body mission will be more scientifically demanding but less technologically challenging than Hayabusa New challenges include touch-and-go sampling for preserving depth profile and hydrated minerals and organic compounds underground Also determining and characterizing sampling sites by both spacecraft remote sensing and micro rovers carrying the surface science package become more important for gaining scientific values of returned samples Once we have actual samples from known S-type and C-type asteroids in ground laboratories in the next decade we should be able to bridge taxonomy of asteroids by spectral observation and meteoritic classifications in the two most major
    12/2013; 36:3426.
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    LPI Contributions. 12/2013;
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    ABSTRACT: Ligation of 2,6-diphenylbenzenethiol (DppSH) onto Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) and subsequent core etching yielded a single cluster Au25(SDpp)11. High-energy X-ray diffraction measurement showed that Au25 constitutes a core in Au25(SDpp)11. We propose a bi-icosahedral Au25 core whose 22 Au surface atoms are capped directly by 11 bulky arenethiolates.
    Chemical Communications 12/2013; · 6.38 Impact Factor
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    ABSTRACT: A high-precision spin-coater system has been developed for the investigation of formation mechanisms of self-assembled structures in polymer thin films. The spin coater was designed to have small axial deflection (<2.6 µm at the maximum speed of 2000 r min−1) during rotation in order to maintain the relative position with respect to the incident X-ray beam, and to be compact (70 mm) in height to facilitate incorporation into an in situ synchrotron radiation grazing-incidence small-angle X-ray scattering (GISAXS) system. The first results of simultaneous measurements on the morphology and film thickness of a triblock copolymer with time resolution of 64 ms during thin-film formation at 2000 r min−1 provide indispensable information for understanding the vertically grown lamellar structure on the film surface.
    Journal of Applied Crystallography 12/2013; 46(6). · 3.95 Impact Factor
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    ABSTRACT: Alkali-metal-intercalated FeSe materials, (NH_{3})_{y}M_{0.4}FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH_{3} technique. (NH_{3})_{y}Cs_{0.4}FeSe shows a superconducting transition temperature (T_{c}) as high as 31.2 K, which is higher by 3.8 K than the T_{c} of nonammoniated Cs_{0.4}FeSe. The T_{c}s of (NH_{3})_{y}K_{0.4}FeSe and (NH_{3})_{y}Rb_{0.4}FeSe are almost the same as those of nonammoniated K_{0.4}FeSe and Rb_{0.4}FeSe. The T_{c} of (NH_{3})_{y}Cs_{0.4}FeSe shows a negative pressure dependence. A clear correlation between T_{c} and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity.
    Physical Review B 09/2013; 88(9). · 3.66 Impact Factor
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    ABSTRACT: Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al-O is stronger than that of Ca-O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71-74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.
    Proceedings of the National Academy of Sciences 05/2013; · 9.81 Impact Factor
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    ABSTRACT: Mineral calaverite AuTe2 is a layered compound with an incommensurately modulated structure. The modulation is characterized by the formation of molecular-like Te2 dimers. We have found that the breaking of Te2 dimers that occurs in Au1-xPtxTe2 results in the emergence of superconductivity at Tc = 4.0 K.
    Journal of the Physical Society of Japan 05/2013; · 1.48 Impact Factor
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    ABSTRACT: Ionic-liquid gates have a high carrier density due to their atomically thin electric double layer (EDL) and extremely large geometrical capacitance Cg. However, a high carrier density in graphene has not been achieved even with ionic-liquid gates because the EDL capacitance CEDL between the ionic liquid and graphene involves the series connection of Cg and the quantum capacitance Cq, which is proportional to the density of states. We investigated the variables that determine CEDL at the molecular level by varying the number of graphene layers n and thereby optimising Cq. The CEDL value is governed by Cq at n < 4, and by Cg at n > 4. This transition with n indicates a composite nature for CEDL. Our finding clarifies a universal principle that determines capacitance on a microscopic scale, and provides nanotechnological perspectives on charge accumulation and energy storage using an ultimately thin capacitor.
    Scientific Reports 04/2013; 3:1595. · 5.08 Impact Factor
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    ABSTRACT: We have developed a fast scanning microscopic X-ray absorption fine-structure (XAFS) measurement system using a 100-300 nm focused X-ray beam at the BL39XU nano-scale analysis station at SPring-8. This system provides two-dimensional XAFS images constructed from X-ray fluorescence (XRF) images measured by fast continuous 2-dimensional scanning at all XAFS measurement energies. High-quality XAFS spectra at each position were obtained by correcting shift in the XRF images. We applied our proposed method to measuring single catalyst particles, and succeeded in measuring the microscopic x-ray absorption near-edge structure (XANES) images that were 2-4 μm square with a spatial resolution of 300 nm.
    Journal of Physics Conference Series 04/2013; 430(1):2019-.
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    ABSTRACT: We upgraded the hard X-ray spectroscopy beamline BL39XU at SPring-8 by installing Kirkpatrick-Baez mirrors to equip it with submicron-focusing capability. At the new experimental end-station located 74 m from the undulator source, an X-ray nanoprobe with a size of 120 × 100 nm2 has become available at 5-16 keV. This upgrade is fully compatible with the X-ray polarization tunability and helicity-switching between right- and left-circular polarizations; these are unique features of the beamline, which is equipped with a diamond X-ray phase retarder. A spatial resolution of ≈100 nm for X-ray absorption fine structure and X-ray magnetic circular dichroism (XMCD) spectroscopy has been achieved. We show a magnetization reversal process of an individual magnetic dot in bit-patterned perpendicular recording media using element-specific XMCD magnetization measurements to demonstrate the performance of the new station.
    Journal of Physics Conference Series 04/2013; 430(1):2017-.
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    ABSTRACT: Advanced nano-scale analyses such as x-ray absorption fine structure (XAFS), x-ray magnetic circular dichroism (XMCD) spectroscopy and x-ray fluorescence (XRF) with a ~100 nm spatial resolution have been routinely conducted by upgrading two x-ray beamlines BL37XU and BL39XU at SPring-8. The focusing beam size can be varied from 50 nm to 2 μm and high flux achieved at 1012 photons/s/0.01% b.w. with the beam size of 300 × 300 nm2 (full width at half maximum) at 12 keV.
    Journal of Physics Conference Series 03/2013; 425(5):052018.
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    ABSTRACT: Field-effect transistor (FET) devices using thin crystals of FeSe1−xTex (x = 0.9 and 1.0) have been fabricated with an electric-double-layer (EDL) capacitor. Despite the presence of substantial quantities of electron and hole carriers in the bulk due to the semimetallic electronic structure of FeSe1−xTex, we have observed p-channel depletion-type FET characteristics, in contrast to the n-channel normally on FET characteristics of a Bi2Se3 EDL FET. In FeSe1−xTex, the mobile carriers, holes, are depleted in the channel region by accumulating electrons, resulting in a decrease in conductivity. This result is consistent with the experimentally observed positive Hall coefficient at room temperature.
    Applied Physics Letters 03/2013; 102(10). · 3.52 Impact Factor

Publication Stats

2k Citations
551.37 Total Impact Points


  • 2011–2014
    • Japan Synchrotron Radiation Research Institute (JASRI)
      Tatsuno, Hyōgo, Japan
    • The Electrochemical Society
      Society Hill, New Jersey, United States
  • 2004–2013
    • Okayama University
      • • Research Center of New Functional Materials for Energy Production, Storage, and Transport
      • • Laboratory for Surface Science
      • • Department of Chemistry
      Okayama, Okayama, Japan
  • 2002–2012
    • Japan Advanced Institute of Science and Technology
      • School of Materials Science
      KMQ, Ishikawa, Japan
  • 2003–2007
    • Osaka University
      • The Institute of Scientific and Industrial Research (ISIR)
      Ibaraki, Osaka-fu, Japan
    • Tohoku University
      • Institute for Materials Research
      Sendai-shi, Miyagi-ken, Japan
  • 2005–2006
    • Japan Aerospace Exploration Agency
      • Institute of Space and Astronautical Science (ISAS)
      Chōfu, Tokyo-to, Japan
    • RIKEN
      Вако, Saitama, Japan
  • 1999–2002
    • The University of Tokyo
      • Department of Physics
      Tokyo, Tokyo-to, Japan
  • 2001
    • Tokyo Metropolitan University
      • Department of Physics
      Tokyo, Tokyo-to, Japan
    • The University of Arizona
      Tucson, Arizona, United States
  • 2000
    • Kobe University
      Kōbe, Hyōgo, Japan