Akihiko Fujiwara

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

Are you Akihiko Fujiwara?

Claim your profile

Publications (214)518.41 Total impact

  • Source
    [Show abstract] [Hide abstract]
    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.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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$_2$.
    02/2014;
  • [Show abstract] [Hide abstract]
    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; · 4.59 Impact Factor
  • H. Yano, M. Abe, A. Fujiwara
    [Show abstract] [Hide abstract]
    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.
  • Source
    LPI Contributions. 12/2013;
  • [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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). · 3.34 Impact Factor
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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.
    05/2013;
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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-.
  • [Show abstract] [Hide abstract]
    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-.
  • Source
    [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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). · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene has two kinds of edges which have different electronic properties. A singular electronic state emerges at zigzag edges, while it disappears at armchair edges. We study the edge-dependent transport properties in few-layer graphene by applying a side gate voltage to the edge with an ionic liquid. The devices indicating a conductance peak at the charge neutrality point have zigzag edges, confirmed by micro-Raman spectroscopy mapping. The hopping transport between zigzag edges increases the conductance.
    Nano Letters 02/2013; · 13.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Al oxide (Al-O) films used as catalyst-support layer for vertical growth of carbon nanotubes (CNTs) were characterized by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission, and scanning electron microscopies (TEM and SEM). EB-deposited Al films (20 nm) were thermally-oxidized at 400 o C (10 min, static air) to produce the surface structure of Al-O. The Al-O was found amorphous and after the incorporation with Co catalyst, the grown CNTs were twisted together before vertically grown. The prepared Al-O surface is an electron-acceptor-dominated (oxygen-rich) surface where the formation of active catalyst could be enhanced to promote the vertically aligned CNT growth.
    Advanced Materials Research 01/2013; 620:213-218.
  • Source
    Mohd Asyadi Azam, Akihiko Fujiwara, Tatsuya Shimoda
    [Show abstract] [Hide abstract]
    ABSTRACT: In this manuscript, the effect of potassium hydroxide (KOH) electrolyte concentrations (0.1 M, 1.0 M, and 6.0 M) to the specific gravimetric capacitance of vertically aligned single-walled carbon nanotube (VA-SWCNT) based supercapacitor will be reported. VA-SWCNT electrode was prepared using direct growth technique of alcohol catalytic chemical vapor deposition. It was found that specific gravimetric capacitance of the VA-SWCNT supercapacitors increased with increasing KOH electrolyte concentration. Besides, lower concentration (or viscosity) of the KOH electrolyte may give better stability in charge storage performance; suggesting difference of ion movement inside the VA-SWCNT double-layer system. The capacitance slope (as a function of cyclic voltammetry scan rate) can be improved by lower concentration of the electrolyte.
    International journal of electrochemical science 01/2013; 8:3902-3911. · 3.73 Impact Factor

Publication Stats

2k Citations
518.41 Total Impact Points

Institutions

  • 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
  • 2002–2011
    • 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