研究者詳細 - 山本　崇史

論文 - 山本　崇史

分割表示 58 件中 41 - 58 件目／全件表示 >>

A Neutral Fe(III) Compound Exhibiting A Two-Step Spin Transition and Dielectric Anomalies

Zhao-Yang Li, Jing-Wei Dai, Kevin J. Gagnon, Hong-Ling Cai, Takashi Yamamoto, Yasuaki Einaga, Han-Hua Zhao, Shinji Kanegawa, Osamu Sato, Kim R. Dunbar, Ren-Gen Xiong

Dalton Transactions 42 （ 41 ） 14685 - 14688 2013年10月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1477-9226

The mononuclear ferric compound Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me) ·H2O (1) was synthesized and characterized using powder/single-crystal X-ray diffraction, Mössbauer spectroscopy, differential scanning calorimetry (DSC), and magnetic susceptibility measurements. This photo-responsive compound shows reversible, two-step spin-crossover behaviour. Moreover, dielectric anomalies were observed during the spin transitions, demonstrating the multifunctional properties of compound 1. © 2013 The Royal Society of Chemistry.

Access to Document (DOI)

Modulation of Critical Current Density in Polycrystalline Boron-Doped Diamond by Surface Modification

Keisuke Natsui, Takashi Yamamoto, Takeshi Watanabe, Yoichi Kamihara, Yasuaki Einaga

Physica Status Solidi B 250 （ 8 ） 1943 - 1949 2013年09月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0370-1972

The maximum current flowed with zero resistance, referred to the critical current density, is desired to be sufficiently large in order to apply superconducting wire rods and electromagnets to various devices. Although the critical current density can be enhanced by introduction of non-superconducting impurities, the transition temperature would become diminished in such a case. Here, we report modulation of a critical current density in heavily boron-doped diamonds (BDDs) by changing the surface-termination without introducing any impurity. The surface of a BDD was changed between hydrogen- and oxygen-termination. As a result, the critical current density could be modulated in a reversible manner between the hydrogen- and oxygen-terminated diamonds with maintenance of the superconducting transition temperature. This is because the volume fractions of the superconducting phases were modulated by surface modification. © 2013 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

Access to Document (DOI)

Synthesis and Size Control of Iron(II) Hexacyanochromate(III) Nanoparticles and the Effect of Particle Size on Linkage Isomerism

Matthieu F. Dumont, Olivia N. Risset, Elisabeth S. Knowles, Takashi Yamamoto, Daniel M. Pajerowski, Mark. W. Meisel, Daniel R. Talham

Inorganic Chemistry （AMER CHEMICAL SOC） 52 （ 8 ） 4494 - 4501 2013年04月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0020-1669

The controlled synthesis of monodisperse nano-particles of the cubic Prussian blue analogue iron(II) hexacyanochromate(III) is reported along with a kinetic study, using cyanide stretching frequencies, showing the variations of the activation energy (E-a) of the linkage isomerism as a function of the particle size. Highly reproducible, cubic-shaped iron(11) hexacyanochromate(110 nanocrystals, with sizes ranging from 2 to 50 nm, are synthesized using a microemulsion technique, whereas a bulk synthesis yields nonuniform less monodisperse particles with sizes greater than 100 nm. Monitoring the cyanide stretching frequency with FTIR spectroscopy shows that the rate of isomerization is faster for smaller particles. Moreover, a kinetic analysis at different temperatures (255 K <= T <= 321 K) gives insight into the evolution of E-a with the particle size. Finally, time-dependent powder X-ray diffraction and net magnetization confirm the FTIR observations. The data are interpreted within the concept of a simple two-component model with different activation energies for structures near the surface of the solid and within the bulk.

Access to Document (DOI)

Paramagnetic Phase of a heavy-Fermion Compound, CeFePO, Probed by ⁵⁷Fe Mössbauer Spectroscopy

Tetsuro Nakamura, Takashi Yamamoto, Masanori Matoba, Yasuaki Einaga, Yoichi Kamihara

Journal of the Physical Society of Japan （PHYSICAL SOC JAPAN） 81 （ 6 ） 064714-4pp 2012年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0031-9015

Fe-57 Mossbauer spectroscopy was applied to an iron-based layered compound CeFePO. At temperatures from 9.4 to 293 K, no magnetic splitting was observed in the Mossbauer spectra of CeFePO indicating a paramagnetic phase of the Fe magnetic sublattice. All the spectra were fitted with a small quadrupole splitting, and the Debye temperature of CeFePO was found to be similar to 448 K. The isomer shift at room temperature, 0.32 mm/s, was almost equal to those of LnFeAsO (Ln = La, Ce, Sm). Comparing s-electron density using the isomer shifts and unit cell volumes, it was found that the Fe of CeFePO has a similar valence state to other layered iron-based quaternary oxypnictides except LaFePO.

Access to Document (DOI)

Anodic Oxidation on a Boron-Doped Diamond Electrode Mediated by Methoxy Radicals

Takenori Sumi, Tsuyoshi Saitoh, Keisuke Natsui, Takashi Yamamoto, Mahito Atobe, Yasuaki Einaga, Shigeru Nishiyama

Angewandte Chemie International Edition （WILEY-V C H VERLAG GMBH） 51 （ 22 ） 5443 - 5446 2012年04月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1433-7851

Access to Document (DOI)

Photomagnetic K_0.25Ni_1-xCo_x[Fe(CN)₆]•nH₂O and K_0.25Co[Fe(CN)₆]_0.75y[Cr(CN)₆]_0.75(1-y)•nH₂O Prussian Blue Analogue Solid Solutions

Daniel. M. Pajerowski, Takashi Yamamoto, Yasuaki Einaga

Inorganic Chemistry （AMER CHEMICAL SOC） 51 （ 6 ） 3648 - 3655 2012年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0020-1669

Magnetically bistable solid solutions of Prussian blue analogues with chemical formulas of KaNi1-xCox[Fe(CN)(6)](beta)center dot nH(2)O (Ni1-xCoxFe) and K alpha Co gamma[Fe(CN)(6)](y)[Cr(CN)(6)](1-y)center dot nH(2)O (CoFeyCr1-y) have been synthesized and studied using mass spectrometry, Mossbauer spectroscopy, X-ray diffraction, temperature-dependent infrared spectroscopy, and dc magnetometry. These compounds provide insight into interfaces between the photomagnetic Co-Fe Prussian blue analogue and the high-T-C Ni-Cr Prussian blue analogue that exist in high-T-C photomagnetic heterostructures. This investigation shows that the bistability of Co-Fe is strongly modified by metal substitution, with Ni1-xCoxFe stabilizing high-spin cobalt-iron pairs and CoFeyCr1-y stabilizing low-spin cobalt iron pairs, while both types of substitution cause a dramatic decrease in the bistability of the material.

Access to Document (DOI)

Electronic Conductivity in Berlin Green and Prussian Blue

Daniel. M. Pajerowski, Takeshi Watanabe, Takashi Yamamoto, Yasuaki Einaga

Physical Review B （AMER PHYSICAL SOC） 83 （ 15 ） 153202-4pp 2011年04月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1098-0121

We report the temperature dependent (100-300 K) conductivity of Berlin green and Prussian blue powders. The method of electronic conduction in vacuum dried Berlin green is identified as hopping of localized electrons and vacuum dried Prussian blue is reaffirmed as an insulator. The assignment of the conduction mechanism is based upon fits to the experimental data, and the different conductivities of the two samples can be understood in terms of both molecular and simple crystalline energy levels of the solids.

Access to Document (DOI)

Block Copolymer Permeable Membrane with Visualized High-Density Straight Channels of Poly(ethylene oxide)

Takashi Yamamoto, Taro Kimura, Motonori Komura, Yukimitsu Suzuki, Tomokazu Iyoda, Sadayuki Asaoka, Haruyuki Nakanishi

Advanced Functional Materials （WILEY-BLACKWELL） 21 （ 5 ） 918 - 926 2011年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1616-301X

A simple fabrication, scalable to centimeter scale, of a permeable membrane made of block copolymer containing molecular transport channels is demonstrated by coating photo-crosslinkable liquid-crystalline block copolymer, consisting of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) bearing stilbene (Stb) mesogens in the side chains (PEO(114)-b-PMA(Stb)(52)), onto a sacrificial cellulose acetate film substrate. After thermal annealing, perpendicularly aligned and hexagonally arranged PEO cylindrical domains with a surface density of 10(11) cm(-2) were formed and then fixed efficiently by photo-crosslinking the stilbene moieties in the PMA(Stb) domains by [2 + 2] dimerization. The fully penetrating straight PEO cylindrical domains across the 480-nm-thick membrane were well-defined and visualized as molecule-transport channels. After exfoliated by removal of the cellulose acetate layer, the membrane could be transferred onto another substrate by either scooping or a horizontal lifting method. Throughout the processes, the fully penetrating PEO channels across the membrane are preserved to open at both ends. A simple permeation experiment demonstrates that rhodamine dyes permeate efficiently through the PEO cylindrical channels of the annealed membrane but not across a non-annealed one.

Access to Document (DOI)

Photoreduction of Prussian Blue Intercalated into Titania Nanosheet Ultrathin Films

Takashi Yamamoto, Naoki Saso, Yasushi Umemura, Yasuaki Einaga

Journal of the American Chemical Society （AMER CHEMICAL SOC） 131 （ 37 ） 13196 - 13197 2009年08月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0002-7863

Ultrathin fims composed of titania nanosheets and Prussian Blue were prepared by using the modified Langmuir-Blodgett technique. The ultrathin films could be deposited in a layer-by-layer manner with lamellar structure. Upon band gap excitation of titania nanosheets, the generated electrons were injected into ferromagnetic Prussian Blue, resulting in reduction to paramagnetic Prussian White. It was revealed that the reaction could proceed only in the presence of hole-scavenging interlayer water molecules.

Access to Document (DOI)

Langmuir–Blodgett Films of Molecular Organic Materials

Daniel R. Talham, Takashi Yamamoto, Mark W. Meisel

Journal of Physics: Condensed Matter （IOP PUBLISHING LTD） 20 （ 18 ） 184006-13pp 2008年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0953-8984

Langmuir-Blodgett methods are perhaps the original approach for achieving controlled deposition of organic thin films. Molecules are first organized into a monolayer array on the surface of water before transfer as a monolayer onto solid supports. Molecular monolayers, multilayers, and multilayered heterostructures can be achieved. The capability of exercising such control over thin film assemblies has attracted materials chemists and physicists to develop Langmuir-Blodgett films for studies on organic conductors, magnets, non-linear optics, rectifiers, and intermolecular electron transfer. This article reviews objectives in each of these areas and selects some specific examples from the literature to highlight the state of the art, mostly from the point of view of the chemical systems that are studied. Mixed organic/inorganic hybrid films represent a new direction for Langmuir-Blodgett films in materials science, combining conventional inorganic solid-state phenomena with the properties of the organic networks, and recent examples, taken principally from the authors' work, are highlighted.

Access to Document (DOI)

Normal Photochromism of Spiropyran in Montmorillonite Interlayer

Naoki Saso, Takashi Yamamoto, Yasushi Umemura, Yasuaki Einaga

Colloids and Surfaces A: Physicochemical and Engineering Aspects （ELSEVIER SCIENCE BV） 317 （ 1-3 ） 309 - 315 2008年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0927-7757

Spiropyran-montmorillonitehybrid materials have been fabricated by the Langmuir-Blodgett(LB) and an intercalation method. The LB method using clay minerals could be applied to fabricate hybrid ultrathin films consisting of a non-amphiphilic spiropyran. It is confirmed that hybrid LB films possess the layered structure and exhibit "normal photochromism" without any changes in the layered structure. In case of the intercalation method, hybrid compounds also possess the layered structure. Interestingly, intercalation hybrid compounds exhibit "reverse photochromism". It is suggested that a different process in formation of the layered structure influences the observed photochromism. (C) 2007 Elsevier B.V. All rights reserved.

Access to Document (DOI)

Photomagnetic Hybrid Ultrathin Films

Takashi Yamamoto, Yasuaki Einaga

Journal of Solid State Electrochemistry （SPRINGER） 11 （ 6 ） 781 - 790 2007年06月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1432-8488

Two novel types of photomagnetic hybrid ultrathin film (film A and B) of metal cyanides have been fabricated by means of the modified Langmuir-Blodgett method using a smectite clay mineral. Film A is composed of an amphiphilic azobenzene cation, a montmorillonite, and Prussian Blue in which photocontrol in the magnetization was realized by the photoisomerization of azobenzene chromophore. The observed photomagnetic efficiency was large (ca. 11%) due to the well-organized structure of the ultrathin film. Film B is composed of a quaternary ammonium salt, a montmorillonite, and Co-Fe Prussian Blue in which the photoinduced magnetization caused by the electron transfer exhibited an anisotropic response with regards to the direction of the applied magnetic field. This phenomenon is ascribed to the unique structure of Co-Fe Prussian Blue formed onto the clay layer.

Access to Document (DOI)

Photochromism Induced Magnetization Changes in Prussian Blue Ultrathin Films Fabricated into the Langmuir–Blodgett Films Composed of an Amphiphilic Azobenzene and a Deoxyribonucleic Acid

Takashi Yamamoto, Yasushi Umemura, Masaru Nakagawa, Tomokazu Iyoda, Yasuaki Einaga

Thin Solid Films （ELSEVIER SCIENCE SA） 515 （ 13 ） 5476 - 5483 2007年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0040-6090

A photomagnetic ultrathin film consisting of an azobenzene, a deoxyribonucleic acid, and Prussian Blue has been fabricated by the Langmuir-Blodgett method. Prussian Blue layers in the films were a two-dimensional structure with the height of 50 A and the average coherence length of 210 A. Reversible photoisomerization of the azobenzenes was observed even in the films. The films exhibit the long-range ferromagnetic order below 4.2 K and moreover, upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 1.0%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization. (C) 2007 Elsevier B.V. All rights reserved.

Access to Document (DOI)

Photomagnetic Langmuir–Blodgett Films Consisting Azobenzene and Prussian Blue: Correlation Between the Film Structure and the Photomagnetic Efficiency

Takashi Yamamoto, Yasushi Umemura, Osamu Sato, Yasuaki Einaga

Science and Technology of Advanced Materials （NATL INST MATERIALS SCIENCE） 7 （ 3 ） 134 - 138 2006年03月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 1468-6996

A photomagnetic organized thin film consisting of an amphiphilic azobenzene, a smectite clay, and Prussian Blue has been prepared by utilizing the Langmuir-Blodgett (LB) method and an ion-exchange reaction. The magnetic LB films were revealed to possess an organized layered structure, and reversible photoisomerization of the azobenzene was observed even in the LB films. Upon photoillumination at 2 K, reversible changes in the magnetization were realized with the value of ca. 11%. This photoswitching in the magnetization is due to changes in the electrostatic field induced by photoisomerization of the azobenzene. A large photoinduced change in the magnetization would be owing to the highly ordered structure of the LB films. In order to verify the correlation between the film structure and photoswitching efficiency, the LB films have been fabricated in other condition. As results, it is confirmed that the packing state of the azobenzene plays an important and crucial role in accomplishment of the highly efficient photomagnetic switching. (c) 2006 Elsevier Ltd. All rights reserved.

Access to Document (DOI)

Observation of the Anisotropic Photoinduced Magnetization Effect in Co–Fe Prussian Blue Thin Films Fabricated by Using the Clay Langmuir–Blodgett Films as a Template

Takashi Yamamoto, Yasushi Umemura, Osamu Sato, Yasuaki Einaga

Journal of the American Chemical Society （AMER CHEMICAL SOC） 127 （ 46 ） 16065 - 16073 2005年11月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0002-7863

Thin films of cobalt-iron cyanide (Co-Fe Prussian blue) have been fabricated by means of the modified Langmuir-Blodgett (LB) method using a smectite clay mineral (montmorillonite). In this combined method, clay LB films play a template role in the formation of the Co-Fe Prussian blue thin layer. The films were revealed to possess a well-organized structure not only in perpendicular directions to the film surface but also in parallel directions to the film surface. The photoinduced electron transfer from the iron ion to the cobalt through the bridging cyanide in the films occurred at low temperature (8 K), similar to that in the bulk Co-Fe Prussian blue. The films clearly exhibited magnetic anisotropy with regards to the direction of the applied magnetic field. Moreover, the photoinduced magnetization effect in the films was also found to be anisotropic.

Access to Document (DOI)

Photomagnetic Co–Fe Prussian Blue Thin Films Fabricated by the Modified Langmuir–Blodgett Technique

Takashi Yamamoto, Yasushi Umemura, Osamu Sato, Yasuaki Einaga

Chemistry Letters （CHEMICAL SOC JAPAN） 33 （ 5 ） 500 - 501 2004年05月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0366-7022

Co-Fe Prussian blue thin films have been prepared by means of a modified Langmuir-Blodgett technique, in which the hybrid monolayer composed of amphiphiles and clay platelets plays a template role for the formation Co-Fe Prussian blue thin films. Photoinduced magnetization was observed in the thin films as observed in the bulk Co-Fe Prussian blue. To the best of our knowledge, this is the first example Of Successful formation of Co-Fe Prussian blue thin films, which possess the ordered structure and, in addition, exhibit photoinduced magnetization.

Access to Document (DOI)

Photoswitchable Magnetic Films: Prussian Blue Intercalated in Langmuir-Blodgett Films Consisting of an Amphiphilic Azobenzene and a Clay Mineral

Takashi Yamamoto, Yasushi Umemura, Osamu Sato, Yasuaki Einaga

Chemistry of Materials （AMER CHEMICAL SOC） 16 （ 7 ） 1195 - 1201 2004年04月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0897-4756

A novel photocontrollable magnetic thin film consisting of amphiphilic azobenzene cations, a smectite clay, and Prussian Blue has been designed and prepared by using the Langmuir-Blodgett method and an ion-exchange reaction. This magnetic thin film possesses a well-organized nanoscale layered structure. Reversible photoisomerization of the azobenzene chromophore realized photoswitching of the magnetization. The changes in the magnetization values were estimated to be ca. 11%. This figure was much larger than our previous system, which contained azobenzene multi-bilayered vesicles in a poly(vinyl alcohol) matrix (J. Am. Chem. Soc. 1999, 121, 3745). These larger changes in the magnetization values are due to the highly ordered structure of the hybrid multilayered films.

Access to Document (DOI)

Reversible Photocontrollable Magnetic Vesicles Consisting of Azobenzene

Yasuaki Einaga, Takashi Yamamoto, Takeshi Sugai, Osamu Sato

Chemistry of Materials （AMER CHEMICAL SOC） 14 （ 11 ） 4846 - 4850 2002年11月

研究論文（学術雑誌）, 共著, 査読有り, ISSN 0897-4756

Photochromic magnetic vesicles have been designed by intercalation of Prussian blue into a lipid bilayer membrane which consists of azobenzene. Reversible photoisomerization of the solid system realized reversible photocontrol of the magnetic properties. Here, we have synthesized an amphiphile azo moiety containing a long alkyl chain, and we have prepared photochromic magnetic vesicles consisting of only this azo moiety. As a result, the magnetic property change brought about by visible light illumination was estimated to be ca. 13%, which is much larger than the figure achieved for the similar system that we reported previously (similar to1%), which contained the double-chain ammonium amphiphile.

Access to Document (DOI)

　前のページ - 次のページ　

山本 崇史

論文 - 山本 崇史

山本　崇史

論文 - 山本　崇史