研究者詳細 - 長田　実

論文 - 長田　実

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Advanced capacitor technology based on two-dimensional nanosheets 査読有り Open Access

Hyung-Jun Kim, Minoru Osada, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS 55 巻 ( 11 ) 2016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：IOP PUBLISHING LTD

As electronics continue to decrease in size, new classes of materials are necessary to continue this downsizing trend. Of particular importance is the development of high-performance capacitors based on dielectric films. Ultrathin high-k dielectrics are expected to be key to future applications. Recently, we have developed new high-k nanodielectrics based on molecularly thin oxide nanosheets [Ti0.87O2, Ti2NbO7, (Ca, Sr)(2)Nb3O10]. Newly developed nanosheets exhibited the highest permittivity (epsilon(r) > 100) ever realized in all known dielectrics in the ultrathin region (<10 nm). In this review, we present recent progress in dielectric nanosheets, highlighting emerging functionalities in capacitor applications. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.1102A3

Highly (0001)-oriented Al-doped ZnO polycrystalline films on amorphous glass substrates 査読有り

Junichi Nomoto, Katsuhiko Inaba, Minoru Osada, Shintaro Kobayashi, Hisao Makino, Tetsuya Yamamoto

JOURNAL OF APPLIED PHYSICS 120 巻 ( 12 ) 2016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：AMER INST PHYSICS

Very thin aluminum-doped zinc oxide (AZO) films with a well-defined (0001) orientation and a surface roughness of 0.357 nm were deposited on amorphous glass substrates at a temperature of 200 degrees C by radio frequency magnetron sputtering, which are promising, particularly in terms of orientation evolution, surface roughness, and carrier transport, as buffer layers for the subsequent deposition of highly (0001)-oriented AZO polycrystalline films of 490 nm thickness by direct current (DC) magnetron sputtering. Sintered AZO targets with an Al2O3 content of 2.0 wt. % were used. DC magnetron sputtered AZO films on bare glass substrates showed a mixed (0001) and the others crystallographic orientation, and exhibited a high contribution of grain boundary scattering to carrier transport, resulting in reduced Hall mobility. Optimizing the thickness of the AZO buffer layers to 10 nm led to highly (0001)-oriented bulk AZO films with a marked reduction in the above contribution, resulting in AZO films with improved Hall mobility together with enhanced carrier concentration. The surface morphology and point defect density were also improved by applying the buffer layers, as shown by atomic force microscopy and Raman spectroscopy, respectively. Published by AIP Publishing.

DOI： 10.1063/1.4962943

Synthesis of green emission upconversion phosphor nanosheets (LaNb2O7) doped with Er3+ and Yb3+ 査読有り

Soichi Takasugi, Riku Iida, Koji Tomita, Michio Iwaoka, Kiyofumi Katagiri, Minoru Osada, Masato Kakihana

JOURNAL OF LUMINESCENCE 173 巻頁： 130 - 134 2016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：ELSEVIER SCIENCE BV

LaNb2O7:Er3+,Yb3+ upconversion (UPC) phosphor nanosheets were prepared by exfoliating a KLaNb2O7: Er3+,Yb3+ layered compound. Highly crystalline nanosheets with a thickness and lateral size of 3.91 nm and approximately 300 nm, respectively, were obtained. The UPC emission intensity of the nanosheets was 7.6 times greater than that of mechanically milled particles (100-500 nm) of bulk KLaNb2O7:Er3+, Yb3+. The UPC emission intensities of the nanosheets dispersed in different solvents (H2O, D2O, CH3OH, CH2Cl2, and CCI4) were measured, and the intensities were observed to decrease in the order CCl4 > CH2Cl2 > D2O > CH3OH > H2O. Because of the large surface area of the nanosheets, their emission intensity was decreased depending on the solvent's vibrational energy. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2015.12.028

Thermally stable dielectric responses in uniaxially (001)-oriented CaBi4Ti4O15 nanofilms grown on a Ca2Nb3O10- nanosheet seed layer 査読有り Open Access

Junichi Kimura, Itaru Takuwa, Masaaki Matsushima, Takao Shimizu, Hiroshi Uchida, Takanori Kiguchi, Takahisa Shiraishi, Toyohiko J. Konno, Tatsuo Shibata, Minoru Osada, Takayoshi Sasaki, Hiroshi Funakubo

SCIENTIFIC REPORTS 6 巻 2016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

To realize a high-temperature capacitor, uniaxially (001)-oriented CaBi4Ti4O15 films with various film thicknesses were prepared on (100)(c)SrRuO3/Ca2Nb3O10- nanosheet/glass substrates. As the film thickness decreases to 50 nm, the out-of-plane lattice parameters decrease while the in-plane lattice ones increase due to the in-plane tensile strain. However, the relative dielectric constant (epsilon(r)) at room temperature exhibits a negligible degradation as the film thickness decreases to 50 nm, suggesting that epsilon(r) of (001)-oriented CaBi4Ti4O15 is less sensitive to the residual strain. The capacitance density increases monotonously with decreasing film thickness, reaching a value of 4.5 mu F/cm(2) for a 50-nm-thick nanofilm, and is stable against temperature changes from room temperature to 400 degrees C irrespective of film thickness. This behaviour differs from that of the widely investigated perovskite-structured dielectrics. These results show that (001)-oriented CaBi4Ti4O15 films derived using Ca2Nb3O10- nanosheets as seed layers can be made candidates for high-temperature capacitor applications by a small change in the dielectric properties against film thickness and temperature variations.

DOI： 10.1038/srep20713

Influences of high deposition rate on LiCoO2 epitaxial films prepared by pulsed laser deposition 査読有り

Kazunori Nishio, Tsuyoshi Ohnishi, Minoru Osada, Narumi Ohta, Ken Watanabe, Kazunori Takada

SOLID STATE IONICS 285 巻頁： 91 - 95 2016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：ELSEVIER SCIENCE BV

This study exhibits influence of deposition rate on LiCoO2 epitaxial films prepared by pulsed laser deposition. High deposition rates tend to destabilize trivalent Co, resulting in formation of an oxygen-deficient phase with a rock-salt structure as an impurity in the deposited films. Because the oxygen-deficient phase originates from incomplete oxidation, post-annealing in air eliminates the impurity phase. Moreover, since it also improves the crystallinity of the film, the post-annealing enhances the electrode performance of the LiCoO2 films. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2015.06.006

Coexistence of magnetic order and ferroelectricity at 2D nanosheet interfaces 査読有り

B. W. Li, M. Osada, Y. Ebina, S. Ueda, T. Sasaki

J. Am. Chem. Soc. 138 巻頁： 7621-7625 2016年

In situ tuning of magnetization and magnetoresistance in Fe3O4 thin film achieved with all-solid-state redox device

T. Tsuchiya, K. Terabe, M. Ochi, T. Higuchi, M. Osada, Y. Yamashita, S. Ueda, M. Aono

ACS Nano 10 巻頁： 1655-1661 2016年

Hunting for monolayer oxide nanosheets and their architectures Open Access

H. J. Kim, M. Osada, Y. Ebina, W. Sugimoto, K. Tsukagoshi, T. Sasaki

Scientific Reports 6 巻頁： 19402-1 2016年

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

Youn Soo Kim, Mingjie Liu, Yasuhiro Ishida, Yasuo Ebina, Minoru Osada, Takayoshi Sasaki, Takaaki Hikima, Masaki Takata, Takuzo Aida

NATURE MATERIALS 14 巻 ( 10 ) 頁： 1002 - 1007 2015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：NATURE PUBLISHING GROUP

Electrostatic repulsion, long used for attenuating surface friction(1,2), is not typically employed for the design of bulk structural materials. We recently developed a hydrogel(3) with a layered structure consisting of cofacially oriented electrolyte nanosheets(4). Because this unusual geometry imparts a large anisotropic electrostatic repulsion(5) to the hydrogel interior, the hydrogel resisted compression orthogonal to the sheets but readily deformed along parallel shear. Building on this concept, here we show a hydrogel actuator(6-11) that operates by modulating its anisotropic electrostatics(12) in response to changes of electrostatic permittivity associated with a lower critical solution temperature transition(3,14). In the absence of substantial water uptake and release, the distance between the nanosheets rapidly expands and contracts on heating and cooling, respectively, so that the hydrogel lengthens and shortens significantly, even in air. An L-shaped hydrogel with an oblique nanosheet configuration can thus act as a unidirectionally proceeding actuator that operates without the need for external physical biases(15-18).

DOI： 10.1038/NMAT4363

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

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 Open Access

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 Open Access

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 Open Access

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

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