研究者詳細 - 長田　実

論文 - 長田　実

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Mn-doped LiNaGe4O9 as a rare-earth free phosphor: impact of Na-substitution on emission in tetragermanate phase 査読有り

Rie Suzuki, Jun Kunitomo, Yoshihiro Takahashi, Kensaku Nakamura, Minoru Osada, Nobuaki Terakado, Takumi Fujiwara

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 123 巻 ( 1441 ) 頁： 888 - 891 2015年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

We have synthesized Mn4+-doped mixed tetragermanate phases in the Li2Ge4O9-LiNaGe4O9 system, i.e., Li(Li,Na)Ge4O9, by a glass-ceramic technique using stoichiometric precursor glasses, and have examined the effect of substitution of Na on their photoluminescence properties. The tetragermanate phases indicated clear red emission based on a E-2 <-(4)A(2) transition, and the entire substitution resulting in an LiNaGe4O9 phase provided an improvement of quenching temperature for the emission. Furthermore, the LiNaGe4O9 phase synthesized by solid-state reaction showed a high internal quantum yield and red color purity, demonstrating it to be a possible candidate as a rare-earth-free red phosphor. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.888

Spectroscopically and thermometrically observed boson peaks in oxide glass system 査読有り

Kensaku Nakamura, Yoshihiro Takahashi, Nobuaki Terakado, Minoru Osada, Takumi Fujiwara

JAPANESE JOURNAL OF APPLIED PHYSICS 54 巻 ( 8 ) 2015年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

We compare the boson peaks (BPs) observed in low-frequency Raman scattering with the BPs observed in low-temperature specific heat in many oxide glasses. We find a linear correlation of the maximum positions between the Raman BP and specific-heat BP regardless of the constituents. In addition, we show that several chalcogenide and molecular glasses also exhibit the same correlation. The linearity enables us to convert the BPs between different observation techniques, which is expected to provide significant insight into the features of the BP. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.088003

Affects of supercooled liquid state on the properties of the crystallized phase: Microscopic and spectroscopic observations in ZnO-crystallized glass-ceramics 査読有り

Yoshihiro Takahashi, Mikio Kinoshita, Takamichi Miyazaki, Minoru Osada, Nobuaki Terakado, Takumi Fujiwara

APPLIED PHYSICS LETTERS 107 巻 ( 6 ) 2015年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER INST PHYSICS

We examined the crystallization and crystal growth of ZnO in the viscoelastic supercooled liquid (SCL) phase based on microscopic and spectroscopic observations. The resulting glass-ceramics exhibits complex ZnO dendrites that precede the formation of Zn-rich regions because of phase separation. Compressive stresses are concentrated at the interface of ZnO crystals and SCL phase, suggesting that the domains are subject to a resistance during ZnO crystal growth. Defects were detected in the crystallized ZnO and attributed to the suppression of smooth ordering of the Zn-rich regions in the SCL phase. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4928538

Tunable Bandgap Narrowing Induced by Controlled Molecular Thickness in 2D Mica Nanosheets 査読有り

Sang Sub Kim, Tran Van Khai, Vadym Kulish, Yoon-Hyun Kim, Han Gil Na, Akash katoch, Minoru Osada, Ping Wu, Hyoun Woo Kim

CHEMISTRY OF MATERIALS 27 巻 ( 12 ) 頁： 4222 - 4228 2015年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

Bandgap engineering of atomically thin 2D crystals is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here, we report a simple but rather unexpected approach for bandgap engineering of muscovite-type mica nanosheets (KAl3Si3O10(OH)(2)) via controlled molecular thickness. Through density functional calculations, we analyze electronic structures in 2D mica nanosheets and develop a general picture for tunable bandgap narrowing induced by controlled molecular thickness. From conducting atomic force microscopy, we observe an abnormal bandgap narrowing in 2D mica nanosheets, contrary to well-known quantum size effects. In mica nanosheets, decreasing the number of layers results in reduced bandgap energy from 7 to 2.5 eV, and the bilayer case exhibits a semiconducting nature with similar to 2.5 eV. Structural modeling by transmission electron microscopy and density functional calculations reveal that this bandgap narrowing can be defined as a consequence of lattice relaxations as well as surface doping effects. These bandgap engineered 2D mica nanosheets open up an exciting opportunity for new physical properties in 2D materials and may find diverse applications in 2D electronic/optoelectronic devices.

DOI： 10.1021/cm504802j

Artificial design for new ferroelectrics using nanosheet-architectonics concept 査読有り

Yoon-Hyun Kim, Lei Dong, Minoru Osada, Bao-Wen Li, Yasuo Ebina, Takayoshi Sasaki

NANOTECHNOLOGY 26 巻 ( 24 ) 2015年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

Control over the emergence of ferroelectric order remains a fundamental challenge for the rational design of artificial materials with novel properties. Here we report a new strategy for artificial design of layered perovskite ferroelectrics by using oxide nanosheets (high-k dielectric Ca2Nb3O10 and insulating Ti0.87O2) as a building block. We approached the preparation of superlattice films by a layer-by-layer assembly involving Langmuir-Blodgett deposition. The artificially fabricated (Ti0.87O2/Ca2Nb3O10)(2)(Ti0.87O2) superlattices are structurally unique, which is not feasible to create in the bulk form. By such an artificial structuring, we found that (Ti0.87O2/Ca2Nb3O10)(2)(Ti0.87O2) superlattices possess a new form of interface coupling, which gives rise to ferroelectricity with a good fatigue-free characteristic. Considering the flexibility of self-assembled nanosheet interfaces, this technique provides a route to synthesize a new kind of layered ferroelectric oxides.

DOI： 10.1088/0957-4484/26/24/244001

Structural changes and microstructures of Ba<sub>1-<i>x</i></sub> Sr <i><sub>x</sub></i> Al<sub>2</sub>O<sub>4</sub> for 0 < <i>x</i> < 0.4

Tanaka, E; Ishii, Y; Tsukasaki, H; Mori, S; Osada, M; Taniguchi, H; Sato, Y; Kubota, Y

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 66 巻 ( 9 ) 頁： 1355 - 1358 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Korean Physical Society

We have investigated the structural changes and the microstructures of Ba1-xSrxAl2O4 for 0 < x < 0.4 by using transmission electron microscope (TEM) and synchrotron radiation powder X-ray diffraction experiments. The TEM experiments revealed the existence of a structural phase boundary at approximately x = 0.1, at which the superlattice reflection spots at the 1/2 0 0 -type positions change into diffuse streaks along three equivalent <110> directions in the hexagonal structure. In addition, real-space images of Ba1-xSrxAl2O4 for 0 < x < 0.4 reveal that BaAl2O4 should be characterized as a modulated structure with triple-q modulation vectors along the <110> directions and on the other hand, Ba1-xSrxAl2O4 for 0.1 < x < 0.4 be characterized as an intermediate (precursor) state with a rigid unit mode due to structural instability. These experimental results implied that the partial substitution of Sr2+ for Ba2+ should suppress a structural instability due to the AlO4 tetrahedral network and decrease the structural phase transition temperature.

DOI： 10.3938/jkps.66.1355

High-temperature dielectric responses of molecularly-thin titania nanosheet 査読有り

Yoon-Hyun Kim, Minoru Osada, Lei Dong, Hyung-Jun Kim, Takayoshi Sasaki

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 123 巻 ( 1437 ) 頁： 335 - 339 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

We have investigated high-temperature dielectric properties of titania nanosheet (Ti0.87O2), a new class of high-kappa nanomaterials derived from the exfoliation of layered compounds. In-situ characterizations using atomic force microscopy indicate a robust insulating property in a monolayer form of Ti0.87O2 nanosheets even at 200 degrees C. Furthermore, layer-by-layer assembled nanocapacitors exhibit both size-free high-epsilon(r) characteristic (similar to 120) and high insulation resistance (similar to 10(-7) A/cm(2)) at high temperatures up to 250 degrees C. The simultaneous improvement of epsilon(r) and thermal stability in high-kappa nanodielectrics is of critical importance for applications of high-temperature capacitors. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.335

Nanosheet architectonics: a hierarchically structured assembly for tailored fusion materials 査読有り

Minoru Osada, Takayoshi Sasaki

POLYMER JOURNAL 47 巻 ( 2 ) 頁： 89 - 98 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Hierarchical self-assembly is a ubiquitous process in nature that underlies the formation of complex biological structures. In recent decades, scientists have aspired to exploit biomimetic approaches to create new artificial materials with hierarchical structures and tailored properties. However, de novo design of such hierarchically structured materials is still a major challenge. In this Focus Review, we provide an overview of new design principles for hierarchical nanoarchitectures using a layer-by-layer (LbL) assembly of two-dimensional (2D) oxide nanosheets. 2D oxide nanosheets have remarkable potential as building blocks for tailoring fusion materials combined with a range of foreign materials such as organic molecules, gels, polymers, and inorganic and metal nanoparticles. The ability to create functionalized, 2D hierarchical systems will lead to various applications in optoelectronics, spinelectronics, energy and environment technologies.

DOI： 10.1038/pj.2014.111

Dendritic silica nanoparticles synthesized by a block copolymer-directed seed-regrowth approach 査読有り

Wang J., Sugawara-Narutaki A., Shimojima A., Osada M., Ma R., Okubo T.

Langmuir 31 巻 ( 5 ) 頁： 1610 - 1614 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Langmuir

A facile seed regrowth method is presented for the preparation of a new type of colloidal dendritic silica nanoparticles (DSNPs) with unique Konpeito-like morphology and high surface area (â4400 m2 g-1). Growth of silica nanoprotrusions on the surfaces of colloidal silica nanoparticles proceeds by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in the presence of a PEO-PPO-PEO-type block copolymer (Pluronic F127) under controlled pH conditions. The polymers adsorbed on the seed surface play a crucial role in the formation of DSNPs. DSNPs with controllable size (28-85 nm) and narrow size distributions can be obtained by using monodisperse silica nanoparticles with various sizes as seeds. The surface morphology of DSNPs is tunable by changing the concentration of TEOS. Additionally, novel dendritic silica nanochains are prepared using one-dimensionally assembled silica nanoparticles as the seeds.

DOI： 10.1021/la504955b

Design of crystal structures, morphologies and functionalities of titanium oxide using water-soluble complexes and molecular control agents 査読有り

Makoto Kobayashi, Minoru Osada, Hideki Kato, Masato Kakihana

POLYMER JOURNAL 47 巻 ( 2 ) 頁： 78 - 83 2015年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Nature produces materials with excellent physical and chemical properties using water as a medium under ambient temperature and pressure. The current need for more highly functional and compact materials makes the mimicking of natural processes to produce these materials a very interesting approach, not only to obtain highly functionalized materials but also to reduce the environmental impact. Our research group is engaged in the development of new stable water-soluble compounds that follow natural processes for the synthesis of materials using water as a medium. This paper summarizes a hydrothermal synthesis of rutile-type titanium oxide using water-soluble titanium complexes, controlling the crystal morphology by utilizing organic molecules as shape-control agents as well as their speculative formation mechanism and superior dielectric properties of unusually shaped titanium oxide crystals. By recapitulating our results, we indicate that control of the nano-and macro-structures and functional improvement are accomplished through the development of new precursor compounds.

DOI： 10.1038/pj.2014.89

Nano-sized cube-shaped single crystalline oxides and their potentials; composition, assembly and functions (vol 25, pg 1401, 2014) 査読有り

Kazumi Kato, Feng Dang, Ken-ichi Mimura, Yoshiaki Kinemuchi, Hiroaki Imai, Satoshi Wada, Minoru Osada, Hajime Haneda, Makoto Kuwabara

ADVANCED POWDER TECHNOLOGY 26 巻 ( 1 ) 頁： 335 - 335 2015年1月

Thermoresponsive actuation enabled by permittivity switching in an electrostatically anisotropic hydrogel 査読有り

Y. S. Kim, M. Liu, Y. Ishida, Y. Ebina, M. Osada, T. Sasaki, T. Hikima, M. Takata, T. Aida

Nature Mater. 14 巻頁： 1002-1007 2015年

2D Perovskite Nanosheets with Thermally-Stable High-kappa Response: A New Platform for High-Temperature Capacitors 査読有り

Yoon-Hyun Kim, Hyung-Jun Kim, Minoru Osada, Bao-Wen Li, Yasuo Ebina, Takayoshi Sasaki

ACS APPLIED MATERIALS & INTERFACES 6 巻 ( 22 ) 頁： 19510 - 19514 2014年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

We investigated high-temperature dielectric responses of high-kappa perovskite nanosheet (Ca2Nb3O10), an important material platform for postgraphene technology and ultrascale electronic devices. Through in situ characterizations using conducting atomic force microscopy, we found a robust high-temperature property of Ca2Nb3O10 nanosheet even in a monolayer form (similar to 2 nm). Furthermore, layer-by-layer assembled nanocapacitors retained both size-free higher characteristic (similar to 200) and high insulation resistance (similar to 1 x 10(-7) A/cm(2)) at high temperatures up to 250 degrees C. The simultaneous improvement of er and thermal stability in high-kappa nanodielectrics is of critical technological importance, and perovskite nanosheet has great potential for a rational design and construction of high-temperature capacitors.

DOI： 10.1021/am506629g

Chemical Preparation of Ferroelectric Mesoporous Barium Titanate Thin Films: Drastic Enhancement of Curie Temperature Induced by Mesopore-Derived Strain 査読有り

Norihiro Suzuki, Xiangfen Jiang, Rahul R. Salunkhe, Minoru Osada, Yusuke Yamauchi

CHEMISTRY-A EUROPEAN JOURNAL 20 巻 ( 36 ) 頁： 11283 - 11286 2014年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：WILEY-V C H VERLAG GMBH

Mesoporous barium titanate (BT) thin films are synthesized by a surfactant-assisted sol-gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (T-c) of the mesoporous BT reaches approximately 470 degrees C.

DOI： 10.1002/chem.201403308

Nano-sized cube-shaped single crystalline oxides and their potentials; composition, assembly and functions 査読有り

Kazumi Kato, Feng Dang, Ken-ichi Mimura, Yoshiaki Kinemuchi, Hiroaki Imai, Satoshi Wada, Minoru Osada, Hajime Haneda, Makoto Kuwabara

ADVANCED POWDER TECHNOLOGY 25 巻 ( 5 ) 頁： 1401 - 1414 2014年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Nanocrystals, especially with an anisotropic shape such as cubic, are candidates as building blocks for new bottom-up approaches to materials assembly, yielding a functional architecture. Such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here, we report synthesis and characteristics of CeO2, BaTiO3 and SrTiO3 nanocubes and the ordered assemblies. The importance of shape as well as size distribution is clarified for the bottom-up development of 3D fine structures. CeO2 nanocube assemblies with enhanced surface of specified crystal planes such as (100) and (111) would open new surface-dominant devices. BaTiO3 and SrTiO3 nanocubes with narrow size distributions and robust diversity in compositions were obtained. BaTiO3 films made up of ordered nanocube assemblies were fabricated on various substrates by evaporation-induced self-assembly method. Regardless of the substrate, the nanocubes exhibited {100} orientations and a high degree of face-to-face ordering, which remained even after heat treatment at 850 degrees C. The supracrystal films exhibited distinct ferroelectric behaviors. (C) 2014 The Authors. Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. This is an open access article under the CC BY-NC-SA license (http://creativecommons.org/licenses/by-nc-sa/3.0/).

DOI： 10.1016/j.apt.2014.02.006

Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film 査読有り

Hongyang Zhao, Hideo Kimura, Zhenxiang Cheng, Minoru Osada, Jianli Wang, Xiaolin Wang, Shixue Dou, Yan Liu, Jianding Yu, Takao Matsumoto, Tetsuya Tohei, Naoya Shibata, Yuichi Ikuhara

SCIENTIFIC REPORTS 4 巻 2014年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：NATURE PUBLISHING GROUP

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of similar to 1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mossbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at similar to 620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of similar to 400 mV/Oe.cm even at room temperature.

DOI： 10.1038/srep05255

Fabrication and Properties of Microcapacitors with a One-nanometer-thick Single Ti0.87O2 Nanosheet 査読有り

Daisuke Ogawa, Kosho Akatsuka, Tomoteru Fukumura, Minoru Osada, Takayoshi Sasaki, Tetsuya Hasegawa

CHEMISTRY LETTERS 43 巻 ( 3 ) 頁： 307 - 309 2014年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：CHEMICAL SOC JAPAN

The dielectric and insulating properties of a single Ti0.87O2 nanosheet were investigated by fabricating an Au/single Ti0.87O2 nanosheet/Au planar microcapacitor structure. Capacitance and electric measurements of the nanosheet microcapacitor showed reproducibly good performance as a gate insulator: almost frequency-independent capacitance up to 1 MHz and extremely high electric field endurance of >= 20 MV cm(-1).

DOI： 10.1246/cl.130925

High performance silicon-based anodes in solid-state lithium batteries 査読有り

Rinlee B. Cervera, Naoki Suzuki, Tsuyoshi Ohnishi, Minoru Osada, Kazutaka Mitsuishi, Takayoshi Kambara, Kazunori Takada

ENERGY & ENVIRONMENTAL SCIENCE 7 巻 ( 2 ) 頁： 662 - 666 2014年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

Silicon-lithium alloys are one of the most attractive anode materials for next-generation lithium-ion batteries; however, they have demonstrated high performance, only when they are fabricated into nano-sized materials. Here we show that even bulky alloys exhibit high potential that has never been shown in conventional liquid electrolytes, when they are in solid electrolytes.

DOI： 10.1039/c3ee43306d

High thermal robustness of molecularly thin perovskite nanosheets and implications for superior dielectric properties 査読有り

B. W. Li, M. Osada, Y. Ebina, K. Akatsuka, K. Fukuda, T. Sasaki

ACS Nano 8 巻頁： 5449-5461 2014年

All-nanosheet ultrathin capacitors assembled layer-by-layer via solution-based processes 査読有り

C. Wang, M. Osada, Y. Ebina, B. W. Li, K. Akatsuka, K. Fukuda, W. Sugimoto, R. Ma, T. Sasaki

ACS Nano 8 巻頁： 2658-2666 2014年

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