研究者詳細 - 長田　実

論文 - 長田　実

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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

Controlled doping of semiconducting titania nanosheets for tailored spinelectronic materials 査読有り

Minoru Osada, Satoshi Yoguchi, Masayuki Itose, Bao-Wen Li, Yasuo Ebina, Katsutoshi Fukuda, Yoshinori Kotani, Kanta Ono, Shigenori Ueda, Takayoshi Sasaki

NANOSCALE 6 巻 ( 23 ) 頁： 14227 - 14236 2014年

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

Ti1-x-yFexCoyO2 nanosheets are synthesized in which the (Fe/Co) content is systematically controlled in the range of 0 <= x <= 0.4 and 0 <= y <= 0.2. A key feature of this new preparation is the use of (Li/Fe)-, (Fe/Co)- and (Li/Co)-co-substituted layered titanates as starting materials. In exfoliated nanosheets, the composition can be intentionally modified by controlled Fe/Co substitution into Ti sites during the solid-state synthesis of the starting layered compounds. The composition of the host layers is maintained in the subsequent exfoliation process, which is very helpful in the rational design of nanosheets through the use of controlled doping. Through this controlled doping, we achieve exquisite control of the electronic properties of Ti-1-dO(2) nanosheets, including the position of impurity bands, the Fermi energy and ferromagnetic properties. From photoelectron spectroscopy and first-principles studies, we have observed that the use of Fe/Co co-doping with higher Fe and Co oxidation states is necessary to bring the highest occupied Fe/Co impurity states to the Fermi level. This band engineering transforms the Ti1-x-yFexCoyO2 nanosheet into a room-temperature half-metallic ferromagnet, thus accomplishing the main requirements of future spinelectronics.

DOI： 10.1039/c4nr04465g

BaTiO3 nanocube and assembly to ferroelectric supracrystals 査読有り

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

Journal of Materials Research 28 巻 ( 21 ) 頁： 2932 - 2945 2013年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Nanocrystals, especially with an anisotropic shape such as cubic, are candidates for 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 BaTiO3 and SrTiO3 nanocubes and the ordered assemblies as ferroelectric supracrystals. BaTiO3 and SrTiO3 nanocubes with narrow size distributions were obtained in an aqueous process. 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 °C. Piezoresponse force microscopy was carried out on the supracrsytal films to obtain plots of the d 33 piezoelectric coefficient against the poling field, and ferroelectric hysteresis curves were shown. © 2013, Materials Research Society. All rights reserved.

DOI： 10.1557/jmr.2013.299

Tunable and highly reproducible surface-enhanced Raman scattering substrates made from large-scale nanoparticle arrays based on periodically poled LiNbO3 templates 査読有り

Xiaoyan Liu, Kenji Kitamura, Qiuming Yu, Jiajie Xu, Minoru Osada, Nagata Takahiro, Jiangyu Li, Guozhong Cao

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 14 巻 ( 5 ) 2013年10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：NATL INST MATERIALS SCIENCE

This work describes novel surface-enhanced Raman scattering (SERS) substrates based on ferroelectric periodically poled LiNbO3 templates. The templates comprise silver nanoparticles (AgNPs), the size and position of which are tailored by ferroelectric lithography. The substrate has uniform and large sampling areas that show SERS effective with excellent signal reproducibility, for which the fabrication protocol is advantageous in its simplicity. We demonstrate ferroelectric-based SERS substrates with particle sizes ranging from 30 to 70 nm and present tunable SERS effect from Raman active 4-mercaptopyridine molecules attached to AgNPs when excited by a laser source at 514 nm.

DOI： 10.1088/1468-6996/14/5/055011

Investigation of PbTiO3 thin films with reduced and re-oxidized treatment using Raman spectroscopy 査読有り

Ken Nishida, Minoru Osada, Hiroki Moriwake, Joe Sakai, Nobuaki Ito, Masamichi Nishide, Hirotaka Oka, Masashi Matsuoka, Rikyu Ikariyama, Hiroshi Funakubo, Takashi Katoda, Takashi Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 巻 ( 1417 ) 頁： 859 - 862 2013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

Investigations of the lattice dynamics of defects, such as oxygen vacancies, are important to understand the properties of PbTiO3 and related materials. Herein polarized Raman spectra of epitaxial PbTiO3 thin films with reduced and re-oxidized treatment were investigated. The oxygen-reduced spectrum displayed an additional mode related to oxygen vacancies, whereas the re-oxidized spectrum was the same as the initial one. The oxygen vacancy content increases as the intensity of additional mode increases, while the intensity of the B-1 mode related to oxygen ions decreases. First-principles calculations of the phonon mode related to oxygen vacancies support the assignment of the additional mode. (C)2013 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.121.859

Enhanced dielectric response induced by controlled morphology in rutile TiO2 nanocrystals 査読有り

Minoru Osada, Makoto Kobayashi, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 巻 ( 1416 ) 頁： 593 - 597 2013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：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

High-quality rutile TiO2 nanocrystals have been synthesized by a simple hydrothermal treatment of a watersoluble titanium-glycolate complex at 200 degrees C. The obtained samples were composed of rod- or whisker-like nanocrystals. The aspect ratios of these nanocrystals could be controlled by adding glycolic acid. Combined characterizations with X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy revealed the formation of highly phase-pure and well-crystallized rutile nanorods/nanowhiskers with the c-axis orientation. Room-temperature dielectric measurements indicated that the permittivity for the rutile nanowhiskers is similar to 150 at 100 kHz, which is higher than that for the bulk rutile powder. These observations pave a way for morphological controlled rutile nanocrytals to find a broad class of technological uses. (C) 2013 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.121.593

Oxygen vacancies in PbTiO3 thin films probed by resonant Raman spectroscopy 査読有り

Ken Nishida, Minoru Osada, Joe Sakai, Nobuaki Ito, Takashi Katoda, Rikyu Ikariyama, Hiroshi Funakubo, Hiroki Moriwake, Takashi Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 121 巻 ( 1416 ) 頁： 598 - 601 2013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：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

Resonant Raman spectroscopy was applied to evaluate oxygen vacancies in PbTiO3-x thin films that were heat treated in a hydrogen atmosphere at various temperatures. Additional mode related to oxygen vacancies occurred in the resonant Raman measurement condition, and its intensity was in proportion to the oxygen vacancy concentration. This correlation offers a simple and useful probe for oxygen vacancies in oxide-based devices. (C) 2013 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.121.598

Realization of graphene field-effect transistor with high-kappa HCa2Nb3O10 nanoflake as top-gate dielectric 査読有り

Wenwu Li, Song-Lin Li, Katsuyoshi Komatsu, Alex Aparecido-Ferreira, Yen-Fu Lin, Yong Xu, Minoru Osada, Takayoshi Sasaki, Kazuhito Tsukagoshi

APPLIED PHYSICS LETTERS 103 巻 ( 2 ) 2013年7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

A high-quality HCa2Nb3O10 (HCNO) nanoflake (epsilon(r) = 9.1) consisting of high-kappa perovskite nanosheets is adopted as a gate dielectric for graphene-based electronics. A dual-gated device was physically constructed by directly dry-transferring a 22-nm-thick HCNO nanoflake as a top gate dielectric onto graphene. The fabricated graphene field-effect transistor could be operated at biases <1.5V with a gate leakage below 1 pA. The top-gate capacitance and mobility of the dual-gated graphene device at room temperature were estimated to be 367 nF/cm(2) and 2500 cm(2)/V.s, respectively. These results show that HCNO can be employed as an alternative dielectric for graphene-based devices. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4813537

Successive phase transformation in stoichiometric glassy Li2Ge4O9: Isothermal and nonisothermal study 査読有り

Yoshihiro Takahashi, Jun Kunitomo, Takamichi Miyazaki, Minoru Osada, Takumi Fujiwara

JOURNAL OF APPLIED PHYSICS 114 巻 ( 3 ) 2013年7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

Stoichiometric glassy germanate is an important material in geophysics and materials science. Despite the binary Li2O-GeO2 system being primitive, its crystallization mechanism remains undetermined. In this study, we investigated crystallization and structural ordering in glassy ferroelectric Li2Ge4O9. Using isothermally and nonisothermally prepared samples, we demonstrated that the glassy Li2Ge4O9 shows no direct structural change to the stoichiometric phase; it rather forms alpha-GeO2 nanocrystals, i.e., it undergoes successive phase transformation. The results suggest that the metastable immiscibility is related to the ordering that occurs prior to crystallization of the stoichiometric phase. (C) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4813783

Oriented Film Growth of Ba1-xSrxTiO3 Dielectrics on Glass Substrates Using 2D Nanosheet Seed Layer 査読有り

Chulho Jung, Tsuyoshi Ohnishi, Minoru Osada, Kazunori Takada, Takayoshi Sasaki

ACS APPLIED MATERIALS & INTERFACES 5 巻 ( 11 ) 頁： 4592 - 4596 2013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

An approach to fabricate Ba0.5Sr0.5TiO3 (BST) films with a preferred orientation on a glass substrate by pulsed laser deposition was developed. To ensure a preferred crystallographic orientation, we utilized a molecularly thin Ca2Nb3O10 perovskite nanosheet as a seed layer and successfully fabricated BST films with a nearly perfect (100)axis orientation. The 100 nm films after annealing at 450 degrees C in air showed a good dielectric performance (epsilon(r) > 400), which was comparable to the epsilon(r) value of epitaxially grown films with the same thickness. These results indicate that the nanosheet seed layer plays a crucial role in controlled film growth, realizing a nearly intrinsic performance of BST.

DOI： 10.1021/am400849z

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