研究者詳細 - 長田　実

論文 - 長田　実

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Atomic Layer Engineering of Ferroelectricity in Dion-Jacobson Perovskites 査読有り

Morita, S; Urushihara, D; Nishibashi, K; Kobayashi, M; Yamamoto, E; Asaka, T; Nakajima, H; Mori, S; Osada, M

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 146 巻 ( 36 ) 頁： 25221 - 25231 2024年8月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Chemical Society

Recent advances in “hybrid-improper” ferroelectricity in Dion-Jacobson (DJ)-type layered perovskites have caused renewed interest in the search for new ferroelectrics. Here, we present an approach for the tailored synthesis of a new homologous series of DJ-type layered perovskites Cs(Bi2Srn-3)(Tin-1Nb)O3n+1. Starting from CsBi2Ti2NbO10 (n = 3), higher-order homologous phases with n = 4 and 5 were successfully synthesized by repeated solid-state calcination with SrTiO3. Characterizations by X-ray diffraction, electron diffraction, transmission electron microscopy, Raman scattering, and second harmonic generation showed the detailed structural features in Cs(Bi2Srn-3)(Tin-1Nb)O3n+1, and the polar structures could be stabilized by proper or hybrid-improper ferroelectricity, depending on the odd or even number of the perovskite layers. Our results provide important insights into the competition between the different mechanisms and the consequences of the ferroelectric properties in homologous layered perovskites.

DOI： 10.1021/jacs.4c09214

Atomic Layer Engineering of Pd Nanosheets for an Enhanced Hydrogen Evolution Reaction

Ando, S; Yamamoto, E; Kobayashi, M; Osada, M

NANO LETTERS 24 巻 ( 36 ) 頁： 11239 - 11245 2024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：Nano Letters

Thickness control of two-dimensional (2D) metal nanosheets (metallenes) has scientific significance for energy and catalyst applications, yet is unexplored owing to the lack of an efficient approach for the tailored synthesis of metallenes with controlled atomic layers. Here we report a 2D template-directed synthesis of ultrathin Pd nanosheets with well-controlled thicknesses. Molecularly thin single-crystalline Pd nanosheets with well-defined hexagonal morphologies were synthesized via a one-pot method with 2,4,6-trichlorophenyl formate. Such Pd nanosheets were used as hard templates for the tailored synthesis of the Pd nanosheets with controlled thicknesses (9, 11, 13, and 15 atomic layers). Hard X-ray photoelectron spectroscopy and density functional theory calculations revealed unique electronic states in thickness-controlled Pd nanosheets; these states included reduced surface charges to bulk, increased work functions, and decreased d-band centers. Thus, atomic layer engineering of Pd nanosheets enabled the fine-tuning of the surface electronic states to improve the hydrogen evolution reaction.

DOI： 10.1021/acs.nanolett.4c02741

Solid-state surfactant templating for controlled synthesis of amorphous 2D oxide/oxyhydroxide nanosheets 査読有り

Yamamoto, E; Kurimoto, D; Ito, K; Hayashi, K; Kobayashi, M; Osada, M

NATURE COMMUNICATIONS 15 巻 ( 1 ) 頁： 6612 2024年8月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Nature Communications

As a member of 2D family, amorphous 2D nanosheets have received increasing attention due to their unique properties that are distinct from crystalline 2D nanosheets. However, compared with the vast library of crystalline 2D nanosheets, amorphous 2D nanosheets are still infancy due to the lack of an efficient synthetic approach. Here, we present a strategy that yields a library of 10 distinct amorphous 2D metal oxides/oxyhydroxides using solid-state surfactant crystals. A key feature of this process is a stepwise reaction using solid surfactant; the solid-state surfactant crystals have metal ions arranged in the interlayer space, and hydrolysis of the metal ions leads to the formation of isolated clusters in the surfactant crystals via limited condensation reactions. Immersing the surfactant crystals in formamide promotes nanosheet formation through the self-assembly of clusters by templating the morphologies of the crystals generated from surfactants crystals. Our approach opens a flatland in amorphous 2D world.

DOI： 10.1038/s41467-024-51040-2

Ultrafast 2D Nanosheet Assembly via Spontaneous Spreading Phenomenon 査読有り国際共著

Shi, Y; Li, H; Tsunematsu, H; Ozeki, H; Kano, K; Yamamoto, E; Kobayashi, M; Abe, H; Chen, CW; Osada, M

SMALL 20 巻 ( 36 ) 頁： e2403915 2024年7月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Small

In 2D materials, a key engineering challenge is the mass production of large-area thin films without sacrificing their uniform 2D nature and unique properties. Here, it is demonstrated that a simple fluid phenomenon of water/alcohol solvents can become a sophisticated tool for self-assembly and designing organized structures of 2D nanosheets on a water surface. In situ, surface characterizations show that water/alcohol droplets of 2D nanosheets with cationic surfactants exhibit spontaneous spreading of large uniform monolayers within 10 s. Facile transfer of the monolayers onto solid or flexible substrates results in high-quality mono- and multilayer films with high coverages (>95%) and homogeneous electronic/optical properties. This spontaneous spreading is quite general and can be applied to various 2D nanosheets, including metal oxides, graphene oxide, h-BN, MoS2, and transition metal carbides, enabling on-demand smart manufacture of large-size (>4 inchϕ) 2D nanofilms and free-standing membranes.

DOI： 10.1002/smll.202403915

その他リンク： https://onlinelibrary.wiley.com/doi/pdf/10.1002/smll.202403915

ナノシートでつくる高性能日射遮蔽膜

長田実

クリーンエネルギー 33 巻頁： 47 - 50 2024年

無機ナノシートの精密合成と機能材料への応用

長田実

科学と工業 98 巻頁： 35 - 41 2024年

Facile Synthesis of Pd Nanosheets and Implications for Superior Catalytic Activity 査読有り

Ando, S; Yamamoto, E; Kobayashi, M; Kumatani, A; Osada, M

ACS NANO 18 巻 ( 1 ) 頁： 461 - 469 2023年11月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Nano

As a member of the 2D materials family, 2D metal nanosheets (metallenes) have received increasing attention due to their intriguing properties distinct from those of graphene and other inorganic 2D nanosheets. However, the synthesis of metallenes is still challenging, owing to the lack of an efficient synthetic approach. Here we present a facile one-pot approach to the controlled synthesis of Pd nanosheets. A key feature of this process is a stepwise reaction using 2,4,6-trichlorophenyl formate (TCPF); TCPF emits carbon monoxide gas, which acts as both a reductant and a surface capping agent, promoting the anisotropic 2D growth of the Pd nanosheets. Photoemission spectroscopy revealed some peculiar features of the surface charge and valence band states due to suppressed electron transfer at the 2D surface. This surface state caused improved catalytic activity for the hydrogen evolution reaction compared to that of bulk Pd.

DOI： 10.1021/acsnano.3c07861

Gigantic Thermal Shielding in 2D Oxide Nanosheets 査読有り

Hirofumi Tsunematsu, Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Tomohiro Yoshida, Minoru Osada

ACS Nano 17 巻 ( 12 ) 頁： 11396 - 11405 2023年5月

Ultrahigh Energy Storage in 2D High-κ Perovskites 国際誌

Kim, HJ; Morita, S; Byun, KN; Shi, Y; Taniguchi, T; Yamamoto, E; Kobayashi, M; Ebina, Y; Sasaki, T; Osada, M

NANO LETTERS 23 巻 ( 9 ) 頁： 3788 - 3795 2023年5月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Nano Letters

Dielectric capacitors have greater power densities than batteries, and, unlike batteries, they do not utilize chemical reactions during cycling. Thus, they can become ideal, safe energy storage devices. However, dielectric capacitors yield rather low energy densities compared with other energy storage devices such as batteries and supercapacitors. Here, we present a rational approach for designing ultrahigh energy storage capacitors using two-dimensional (2D) high-κ dielectric perovskites (Ca2Nam-3NbmO3m+1; m = 3-6). Individual Ca2Nam-3NbmO3m+1 nanosheets exhibit an ultrahigh dielectric strength (638-1195 MV m-1) even in the monolayer form, which exceeds those of conventional dielectric materials. Multilayer stacked nanosheet capacitors exhibit ultrahigh energy densities (174-272 J cm-3), high efficiencies (>90%), excellent reliability (>107 cycles), and temperature stability (−50-300 °C); the maximum energy density is much higher than those of conventional dielectric materials and even comparable to those of lithium-ion batteries. Enhancing the energy density may make dielectric capacitors more competitive with batteries.

DOI： 10.1021/acs.nanolett.3c00079

DOI： 10.1021/acs.nanolett.3c00079

Single droplet assembly for two-dimensional nanosheet tiling 査読有り国際誌

Shi Yue, Osada Minoru, Ebina Yasuo, Sasaki Takayoshi

ACS Nano 14 巻 ( 11 ) 頁： 15216 - 15226 2020年11月

Ferroelectricity in CsPb<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> and exfoliated 2D nanosheets 査読有り

Li, Y; Shimada, M; Kobayashi, M; Yamamoto, E; Canton-Vitoria, R; Liu, XY; Osada, M

DALTON TRANSACTIONS 2024年9月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Dalton Transactions

Pb-based perovskites play pivotal roles in ferroelectric research. In the search for new Pb-based ferroelectrics, we investigated the ferroelectric properties of Dion-Jacobson type CsPb2Nb3O10 and exfoliated 2D nanosheets. Ferroelectricity in CsPb2Nb3O10 was demonstrated for the first time. CsPb2Nb3O10 adopted a polar tetragonal structure with a modest TC = 260 °C and polarization PS = 7.93 μC cm−2; the polarization mainly arose from the out-of-plane displacements of Nb5+ ions and nearby oxygens. CsPb2Nb3O10 layered perovskite offers additional advantages for tailoring ferroelectric nanomaterials, as exfoliated 2D nanosheets provide novel platforms for investigating ferroelectric properties down to the 2D limit. Piezoresponse force microscopy confirmed stable ferroelectricity even in exfoliated 2D Pb2Nb3O10 nanosheets.

DOI： 10.1039/d4dt02343a

Synthesis of Gold Nanoparticles Using Au(OH)₃ as a Precursor in Aqueous Media 査読有り

スマートプロセス学会誌 13 巻 ( 4 ) 頁： 200 - 204 2024年7月

Autonomous Light Intensity Adaptation in an Energy-Efficient Retinomorphic Organic Ferroelectric Neuristor 査読有り国際共著

Li, LF; Dai, QY; Li, YT; Pei, MJ; Osada, M; Li, Y

ADVANCED OPTICAL MATERIALS 2024年3月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Optical Materials

In biological visual systems, retina with bidirectional photoresponse can adapt to variable environments and modulate their photosensitivity dependent on illumination conditions in an energy-efficient way. However, to emulate the visual functionality, current systems still require a sustained power supply and manipulate the electrical stimulation manually according to light intensity, thus incurring high energy consumption and the lack of autonomous adaptive function. Herein, an organic ferroelectric neuristor emulating the visual self-adaptation function of retina is introduced. Such autonomous adaptive behavior of device originates from the trap-assisted ferroelectric polarization reversal under light illumination. It allows to realize bidirectional photoresponse in a single device according to light intensity, thus breaking through the limitation of commonly adaptive devices with single photoresponse mechanisms. In particular, only a single gate voltage pulse with an ultralow energy consumption of ≈34 pJ is required to accomplish the adaptation behavior, endowing the visual perception with high autonomy and power efficiency. Finally, the application potential of the neuristor in image pre-processing and recognition under bright and dim light conditions is demonstrated. Therefore, this work opens up a path for the development of retina-like visual systems with highly energy efficient.

DOI： 10.1002/adom.202303172

Multiemission of Ce3+ from a Single Crystallographic Site Induced by Disordering of Ions 査読有り

Yasunaga, T; Kobayashi, M; Oqmhula, K; Qi, H; Ichibha, T; Hongo, K; Yamamoto, S; Maezono, R; Mitsuishi, M; Osada, M; Kato, H; Kakihana, M

INORGANIC CHEMISTRY 63 巻 ( 2 ) 頁： 1288 - 1295 2024年1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：Inorganic Chemistry

White-light emission with a single activator is an attractive function of phosphors. In this work, we investigated the photoluminescence properties of Ca5.7Y1.3Si7O16.7N3.3, which is a compound denoted as Ca4+xY3-xSi7O15+xN5-x discovered by our group, with Ce-activation using optical measurements and density functional theory (DFT) calculation. Samples showed a tunable emission from purple to white under ultraviolet (UV) light. In this compound, Ca and Y as well as anions are distributed disorderly, and Ca/Y ions occupy two crystallographically distinct sites; those sites are possible sites for Ce substitution. DFT calculation and structural refinement revealed that the tunable emission was generated by Ce at the crystallographically equivalent site but with distinct local structures caused by the disordering of cations and anions. As far as we know, this is the first report about a white-light-emitting phosphor with only Ce activation.

DOI： 10.1021/acs.inorgchem.3c03789

Understanding the role of solvents in bottom-up synthesis of multi-element hydroxides 査読有り

Li, F; Yoshida, K; Chuc, NV; Osada, M; Abe, H

RSC ADVANCES 14 巻 ( 1 ) 頁： 75 - 82 2024年1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：RSC Advances

Here we report a comparative study on the bottom-up synthesis of multi-element hydroxides composed of Mg, Al, Fe and Zn cations to understand the role of solvents. Two common solvents, water and ethylene glycol, a typical polyol, are used. The polyol-derived MgAlFeZn-OH are nanosheets with homogeneous elemental distribution, while the hydrothermal-derived MgAlFeZn-OH are mixtures of plate-like hydroxide layers and rod-like spinel oxides. The coordinating properties and the high viscosity of the ethylene glycol provide the possibility to mediate the hydrolysis rates and to control the particle growth. The high specific surface area of the polyol-derived multi-element hydroxide nanosheets (352.4 m2 g−1) guarantees them as excellent adsorbents for adsorbing anionic dyes in aqueous solution.

DOI： 10.1039/d3ra07344k

Hetero-assembly design of 2D oxide nanosheets for tailored thermal shielding materials 査読有り

Tsunematsu, H; Nishibashi, K; Yamamoto, E; Kobayashi, M; Yoshida, T; Osada, M

APPLIED PHYSICS EXPRESS 17 巻 ( 1 ) 頁： 015002-1 - 015002-5 2024年1月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

We present a new approach for designing thermal shielding materials using two-dimensional oxide nanosheets. Our approach uses hetero-assembly design [(Ti0.87O2)m (Cs2.7W11O35−d )20 (m = 0, 5, 10)] by overlaying high refractive index (n) Ti0.87O2 nanosheets with transparent conducting Cs2.7W11O35−d nanosheets. Through proper design of the thickness of high-n Ti0.87O2 layers, we achieved the optimum thermal shielding properties with a high NIR reflectance (>46%), a high visible transparency (>76%) and a neutral color in an ultrathin form (<60 nm). Our nanosheet approach is of technological importance for exploring new thermal shielding materials.

DOI： 10.35848/1882-0786/ad13ce

Tuning the structures and conductivity of nanoporous TiO2-TiO films through anodizing electrolytes as LIB anodes with ultra-high capacity and excellent cycling performance 査読有り

Chen, XW; Kure-Chu, SZ; Liu, JC; Matsubara, T; Sakurai, Y; Hihara, T; Lee, SH; Osada, M; Okido, M

JOURNAL OF ENERGY STORAGE 73 巻頁： 109231 2023年12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 Energy Storage

Titanium dioxide (TiO2) is a typical lithium-ion storage material with various advantages including a stable structure, an abundant source, and facile preparation. To further improve the lithium-ion diffusion, we employed a smart anodization method to prepare nanoporous TiO2–TiO (TT) films with a fast growth rate and excellent charge/discharge performance. The key feature is the use of nitric-based electrolytes with the addition of glycine and ethanol, which rapidly form approximately five times thicker TiO2 nanoporous films compared to previous studies. The addition of glycine and ethanol to nitric-based electrolytes improve both the nanoporous structures and conductivity of titania films, thereby forming highly active TiO and a large surface area, which further accelerates the diffusion of lithium ions. As a lithium-ion battery (LIB) anode, the E-G-TT specimen offers the highest initial discharge capacity (3418 μA h−1 cm−2, 30 μA cm−2), which is approximately eight times higher than that of the titania film obtained without additives (TT). Furthermore, a high discharge capacity of >1100 μA h−1 cm−2 can be maintained after 100 cycles, which can be mainly attributed to the enhancement of conductivity and charge transition of the composite films due to the synergistic effect of ethanol and glycine addition.

DOI： 10.1016/j.est.2023.109231

Understanding the fast formation mechanism of hard nanoporous alumina films on aluminum in acidic solutions containing nitric acid 査読有り

Liu, JC; Kure-Chu, SZ; Sakurai, Y; Chen, XW; Osada, M

MATERIALS CHEMISTRY AND PHYSICS 309 巻頁： 128271 2023年11月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Chemistry and Physics

Nanoporous alumina films formed on aluminum via anodization are widely used for scientific and technical purposes owing to their various advantageous properties, including excellent corrosion and wear resistance, good thermal and electrical insulation, and facile producibility at low cost. Herein, we report a novel approach to fabricate hard porous anodic alumina (PAA) films by adding an appropriate amount of nitric acid to sulfuric-, oxalic-, and phosphoric-acid solutions at critical high current densities. The effects of the nitric additives on the anodizing behavior, film growth mechanism, microstructure, chemical composition, film thickness, microhardness, and appearance of the PAA films formed from various solutions were systematically investigated. The addition of nitric acid enhanced the formation of alumina and resulted in fast growth rates of 196 μm/h and 166 μm/h for sulfuric- and oxalic-based solutions, respectively, while maintaining high hardness of approximately 380 and 430 HV0.1, respectively. The surface hardness of the films decreased to some extent with the increase in nitric acid concentration and/or film thickness owing to the strong corrosive nature of nitric acid during prolonged anodization, although nitrogen inclusion in anodic alumina films was not detected through X-ray photo-electron spectroscopy, which differs from the other acidic anions. In particular, the barrier layer thickness and pore intervals of PAA films increased with the nitric concentration in the aforementioned solutions, leading to a fast growth rate and high hardness inside the films.

DOI： 10.1016/j.matchemphys.2023.128271

Emerging ceramic nanosheets: From tailored synthesis to electronic applications 査読有り

Osada, M

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 131 巻 ( 11 ) 頁： 851 - 862 2023年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

Two-dimensional (2D) nanosheets, which possess atomic or molecular thicknesses and infinite lateral lengths, have received increasing attention due to their intriguing physicochemical properties distinct from those of their bulk counterparts. In particular, the discovery of graphene has opened new possibilities for exploring the fascinating properties of 2D nanosheets of other layered and non-layered compounds. 2D inorganic nanosheets (ceramic nanosheets) are important targets in this regard due to their diversity in chemical composition, structure and functionality beyond graphene. Here, we review recent advances in the synthesis, assembly and properties of 2D oxide nanosheets, highlighting emerging functionalities in electronic applications.

DOI： 10.2109/jcersj2.23126

Engineering Interface Defects and Interdiffusion at the Degenerate Conductive In2O3/Al2O3 Interface for Stable Electrodes in a Saline Solution 査読有り

Z. Zhu, T. Yasui, X. Zhao, Q. Liu, S. Morita, Y. Li, A. Yonezu, K. Nagashima, T. Takahashi, M. Osada, R. Matsuda, T. Yanagida, Y. Baba

ACS Applied Materials & Interfaces 15 巻 ( 30 ) 頁： 36866 - 36876 2023年7月

Thermal and Chemical Phase Engineering of Two-Dimensional Ruthenate 査読有り

Leanddas Nurdiwijayanto, Kensuke Hayashi, Nobuyuki Sakai, Yasuo Ebina, Dai-Ming Tang, Shigenori Ueda, Minoru Osada, Kazuhito Tsukagoshi, Takayoshi Sasaki, Takaaki Taniguchi

ACS Nano 17 巻 ( 13 ) 頁： 12305 - 12315 2023年6月

Free-Standing Molecularly Thin Amorphous Silica Nanosheets 査読有り

Yamamoto, E; Fujihara, K; Takezaki, Y; Ito, K; Shi, Y; Kobayashi, M; Osada, M

SMALL 19 巻 ( 22 ) 頁： e2300022 - 2300022 2023年6月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Small

Recent progress in 2D materials has initiated new fields of molecularly thin amorphous materials with mysterious properties and structures. However, designed synthesis of molecularly thin amorphous silica still remains a challenge; whether free-standing molecularly thin amorphous silica nanosheets can exist is unclear. Here, this issue is addressed by using a new chemical protocol; solid-state surfactant lamellae with ordered alkyl-chain arrangements can serve as superior templates guiding free-standing amorphous silica nanosheets. Simple sonication of the lamellar hybrids allows exfoliation into monolayer amorphous silica nanosheets with 0.9 nm thickness. In addition, the nanosheets show the distinctive feature of high colloidal stability that enables atomic layer engineering of silica nanocoatings and dielectric nanofilms. The approach may shed new light on the properties and applications of old silica.

DOI： 10.1002/smll.202300022

DOI： 10.1002/smll.202300022

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/smll.202300022

Layer-dependent stability of 2D mica nanosheets 査読有り国際共著

Jae-Hun Kim, Vadym V Kulish, Shunnian Wu, Ping Wu, Yue Shi, Minoru Osada, Hyoun Woo Kim, Sang Sub Kim

Scientific Reports 13 巻頁： 7880 2023年5月

2D bismuth oxyfluorides: a new member of cationic nanosheets 査読有り

M. Kobayashi, T. Tasaka, E. Yamamoto, M. Osada

Chem. Lett. 52 巻 ( 6 ) 頁： 449 - 451 2023年4月

Pseudo-topotactic Transformation from Oxide Nanosheets to Amorphous Nanosheets 査読有り

Sugimoto, H; Kobayashi, M; Yamamoto, E; Osada, M

CHEMISTRY LETTERS 52 巻 ( 5 ) 頁： 322 - 324 2023年4月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry Letters

We demonstrated the synthesis of amorphous oxide nanosheets from crystalline nanosheets prepared by the exfoliation of layered compounds. Single-crystalline oxide nanosheets were calcined with C3N4 powder in flowing nitrogen and annealed in air to produce amorphous oxide nanosheets. The cation composition and valence, shape, lateral size, surface roughness, and thickness were not changed by treatment. This approach enables the production of amorphous oxide nanosheets with distinct morphologies and compositions and large lateral sizes.

DOI： 10.1246/cl.230073

Molecularly Thin BaTiO3 Nanosheets with Stable Ferroelectric Response 査読有り国際共著

Kazuki Hagiwara, Ki Nam Byun, Shu Morita, Eisuke Yamamoto, Makoto Kobayashi, Xioyang Liu, Minoru Osada

Advanced Electronic Materials 9 巻 ( 4 ) 頁： 2201239 2023年4月

Composite design of two-dimensional inorganic nanosheets for flexible energy storage capacitors 査読有り

Ki-Nam Byun, Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

Journal of the Ceramic Society of Japan 131 巻 ( 4 ) 頁： 77 - 82 2023年4月

Automated One-Drop Assembly for Facile 2D Film Deposition 査読有り

Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

ACS Applied Materials & Interfaces 15 巻 ( 18 ) 頁： 22737 - 22743 2023年3月

Damage-free LED lithography for atomically thin 2D material devices 査読有り

13 巻頁： 2583 2023年2月

Improved energy storage performance of PVDF nanocapacitors by utilizing 2D inorganic barrier 査読有り

Byun Ki-Nam, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

Chemistry Letters 52 巻 ( 1 ) 頁： 51 - 54 2023年1月

Advances in dielectric performance of atomically engineered Sr1. 8Bi0. 2Nb3O10 perovskite nanosheet thin films 査読有り国際共著

Haena Yim, So Yeon Yoo, Haneul Choi, Hye Jung Chang, Seong-Ju Hwang, Sahn Nahm, Minoru Osada, Ji-Won Choi

Journal of Alloys and Compounds 925 巻頁： 166606 2022年12月

Tailored synthesis of molecularly thin platinum nanosheets using designed 2D surfactant solids 査読有り

Eisuke Yamamoto, Akiko Suzuki, Makoto Kobayashi, Minoru Osada

Nanoscale 14 巻頁： 11561 - 11567 2022年6月

無機２次元ナノシートが拓く原子層技術招待有り査読有り

長田　実

まてりあ 60 巻 ( 10 ) 頁： 628 - 633 2021年10月

Construction of multilayer films and superlattice-and mosaic-like heterostructures of 2D metal oxide nanosheets via a facile spin-coating process 査読有り

Hitomi Yano, Nobuyuki Sakai, Yasuo Ebina, Renzhi Ma, Minoru Osada, Kenjiro Fujimoto, Takayoshi Sasaki

ACS Applied Materials & Interfaces 13 巻 ( 36 ) 頁： 43258 - 43265 2021年8月

Solution-Processed Two-Dimensional Metal Oxide Anticorrosion Nanocoating 査読有り

Leanddas Nurdiwijayanto, Hiroki Nishijima, Yoshiharu Miyake, Nobuyuki Sakai, Minoru Osada, Takayoshi Sasaki, and Takaaki Taniguchi

Nano Lett. 21 巻 ( 16 ) 頁： 7044 - 7049 2021年8月

Facile titania nanocoating using single droplet assembly of 2D nanosheets 査読有り

Yue Shi, Eisuke Yamamoto, Makoto Kobayashi, Minoru Osada

J. Ceram. Soc. Jpn. 129 巻 ( 7 ) 頁： 359 - 364 2021年7月

Reversible hydrogenation and irreversible epoxidation induced by graphene oxide electrolysis

T. Taniguchi, K-C. Wong, L. Nurdiwijayanto, K. Hatakeyama, K. Awaya, S. Ida, K. Koiumuma, S. Ueda, M. Osada, H. Yokoi

Carbon 177 巻頁： 26 - 34 2021年2月

焼かずに機能性セラミックスをつくる

長田実

化学と教育 69 巻 ( 1 ) 頁： 24 - 27 2021年1月

担当区分：筆頭著者,　責任著者記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本化学会

<p>機能性セラミックスは，エレクトロニクスから環境・エネルギー，航空・宇宙，医療に至る様々な分野で幅広く活躍している。セラミックスの研究は，古くは粉体，焼結体を扱うバルクから始まり，現在のナノ薄膜の研究へと大きく進展している。特に，近年のナノテクの発展は目覚ましく，原子・分子レベルの構造を自在に操り，新しい機能性セラミックスを開発しようという取り組みが精力的に行われている。本稿では，筆者らのナノ材料の研究を例に，焼かないで機能性セラミックスをつくる新しい技術について紹介したい。</p>

DOI： 10.20665/kakyoshi.69.1_24

Rational assembly of two-dimensional perovskite nanosheets as building blocks for new ferroelectrics 査読有り国際誌

Muhammad Shuaib Khan, Minoru Osada, Lei Dong, Yoon-Hyun Kim, Yasuo Ebina, Takayoshi Sasaki

ACS Appl. Mater. Interfaces 13 巻 ( 1 ) 頁： 1783 - 1790 2021年1月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Artificial materials in the form of superlattices have been studied actively in quest of new engineering methods or design rules for the development of desired functionalities, in particular high-k ferroelectricity, ferromagnetism, and high mobility electron gas. This work presents a controlled assembly strategy for fabricating atomically precise interfaces of two-dimensional (2D) homologous perovskite nanosheets (Ca2Nam-3Nb
m
O3m+1-; m = 3-6) to construct artificial superlattices. The distinctive thickness of each 2D homologous perovskite nanosheets attributed to the presence of different number of NbO6 octahedra provides an exquisite control to engineer interfacial properties for tailored design of superior high-k properties and emergence of ferroelectricity. The higher dielectric constant (εr = 427) and development of ferroelectricity for (Ca2Nb3O10-/Ca2Na2Nb5O16-)6 superlattice indicate that superlattice films with both odd number of NbO6 octahedra possess extended polarization due to the potential effect of heterointerface and ferroelectric instabilities. Furthermore, the increased discontinuities/offsets in Ca2Nb3O10- and Ca2Na3Nb6O19- nanosheets band alignment results in superior insulating properties (∼1 × 10-11 A cm-2 at 1 V) for (Ca2Nb3O10-/Ca2Na3Nb6O19-)6 superlattice. These findings exhibit new research opportunities for the development of novel artificial high-k dielectric/ferroelectric via precise control of interfaces at the atomic level and can be extended to the large family of 2D perovskite compounds.

DOI： 10.1021/acsami.0c16967

焼かずに機能性セラミックスをつくる招待有り査読有り

長田　実

化学と教育 69 巻 ( 1 ) 頁： 24 - 27 2021年1月

無機ナノシートを利用した室温セラミックスコーティング招待有り査読有り

長田　実

セラミックス 55 巻 ( 10 ) 頁： 741 - 745 2020年10月

Scalable design of two-dimensional oxide nanosheets for construction of ultrathin multilayer nanocapacitors 査読有り国際誌

Muhammad Shuaib Khan, Hyung-Jun Kim, Yoon-Hyun Kim, Yasuo Ebina, Wataru Sugimoto, Takayoshi Sasaki, Minoru Osada

Small 16 巻頁： 2003485 2020年8月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Large size of capacitors is the main hurdle in miniaturization of current electronic devices. Herein, a scalable solution-based layer-by-layer engineering of metallic and high-κ dielectric nanosheets into multilayer nanosheet capacitors (MNCs) with overall thickness of ≈20 nm is presented. The MNCs are built through neat tiling of 2D metallic Ru0.95 O20.2- and high-κ dielectric Ca2 NaNb4 O13- nanosheets via the Langmuir-Blodgett (LB) approach at room temperature which is verified by cross-sectional high-resolution transmission electron microscopy (HRTEM). The resultant MNCs demonstrate a high capacitance of 40-52 µF cm-2 and low leakage currents down to 10-5 -10-6 A cm-2 . Such MNCs also possess complimentary in situ robust dielectric properties under high-temperature measurements up to 250 °C. Based on capacitance normalized by the thickness, the developed MNC outperforms state-of-the-art multilayer ceramic capacitors (MLCC, ≈22 µF cm-2 /5 × 104 nm) present in the market. The strategy is effective due to the advantages of facile, economical, and ambient temperature solution assembly.

DOI： 10.1002/smll.202003485

Synthesis of NaMoO3F and Na5W3O9F5 with morphological controllability in non-aqueous solvents. 査読有り国際誌

Y. Asakura, T. Akahira, M. Kobayashi, M. Osada, S. Yin

Inorganic Chemistry 59 巻 ( 15 ) 頁： 10707 - 10716 2020年8月

掲載種別：研究論文（学術雑誌）

NaMoO3F and Na5W3O9F5 were synthesized by solvothermal reaction of MoO3 and WO3, respectively, with NaF in nonaqueous solvents. These reactions were realized at low temperatures (150-200 °C) without the use of HF. This synthesis method is much more facile and safe procedure compared with general synthesis methods for oxyfluorides which includes hydrothermal reaction under a presence of HF or solid-state reaction at high temperatures in vacuum sealed tube or under high pressure. In the case of the reaction of MoO3 with NaF, the kind of solvent largely affected the obtained morphologies of NaMoO3F. The morphology in the case of acetonitrile as a solvent was rodlike with a micrometer-scale size, while that in the case of ethanol was polyhedral with a size of several hundred nanometers. In addition, the solvothermal reaction of WO3 with NaF led to the formation of Na5W3O9F5. Also, the difference of solvents for the solvothermal reaction affected the obtained particle sizes. The effect of the solvents on the morphologies of the obtained oxyfluorides probably resulted from the difference of the solubility of NaF and the subsequent dissolution ratio of MoO3 or WO3 in the used solvents. Our synthesis method can expand the applicability of oxyfluorides by providing a new phase and/or unique morphology.

DOI： 10.1021/acs.inorgchem.0c01175

Graphitic carbon nitride-based low-dimensional heterostructures for photocatalytic applications 査読有り国際誌

M-S. Khan, F. Zhang, M. Osada, S-S. Mao, S. Shen

Solar RRL 4 巻 ( 8 ) 2020年8月

無機ナノシートの精密集積と電子デバイスへの応用招待有り査読有り

長田　実

機能材料 40 巻 ( 7 ) 頁： 15 - 21 2020年7月

On/off boundary of photocatalytic activity between single- and bilayer MoS2 査読有り国際誌

Takaaki Taniguchi, Leanddas Nurdiwijayanto, Shisheng Li, Hong En Lim, Yasumitsu Miyata, Xueyi Lu, Renzhi Ma, Dang-Ming Tang, Shigenori Ueda, Kazuhito Tsukagoshi, Takayoshi Sasaki, Minoru Osada

ACS Nano 14 巻 ( 6 ) 頁： 6663 - 6672 2020年6月

Hard-template synthesis of hollow mesoporous silica nanoplates using layered double hydroxide 査読有り国際誌

Shi Y.

Chemistry Letters 49 巻 ( 9 ) 頁： 1078 - 1080 2020年6月

2次元ナノシートの形態制御と機能材料への応用招待有り査読有り

長田　実

セラミックス 55 巻 ( 5 ) 頁： 390 - 394 2020年5月

van der Waals force layered multiferroic hybrid perovskite (CH3NH3)2CuCl4 single crystals 査読有り国際誌

Zhao Hu, Hongyang Zhao, Zhenxiang Cheng, Jianxu Ding, Han Gao, Yibo Han, Shengao Wang, Zhiwen Xu, Yucheng Zhou, Tingting Jia, Hideo Kimura, Minoru Osada

Physical chemistry chemical physics : PCCP 22 巻 ( 7 ) 頁： 4235 - 4239 2020年4月

担当区分：最終著者掲載種別：研究論文（学術雑誌）

In inorganic-organic perovskites, the three-dimensional arrangement of the organic group results in more subtle balance of charge, spin and space, thereby providing an attractive route toward new multiferroics. Here we report the existing of multiple ferroic orderings in inorganic-organic layered perovskites with relative strong hydrogen bond ordering of the organic chains intra plane. In addition, the inter plane in perovskite is stacking via van der Waals force. However, such magnetoelectric coupling properties for this compound have not been reported since it is difficult to characterize the properties in single crystals since most of the hybrid perovskites are usually deliquescent and unstable when exposed to air. To deal with these problems, we synthesized a (CH3NH3)2CuCl4 single crystal by using a simple evaporation technique, and demonstrated ferroelectric, magnetic and magneto-electric properties of (CH3NH3)2CuCl4. The internal hydrogen bonding of easily tunable organic unit combined with 3d transition-metal layers in such hybrid perovskites make (CH3NH3)2CuCl4 a multiferroic crystal with magnetoelectrical coupling and offer an new way to engineer multifunctional multiferroic.

DOI： 10.1039/c9cp05976h

Guanine crystals regulated by chitin-based honeycomb frameworks for tunable structural colors of sapphirinid copepod, Sapphirina nigromaculata 査読有り国際誌

Kimura Tsubasa, Takasaki Mihiro, Hatai Ryosuke, Nagai Yukiko, Uematsu Katsuyuki, Oaki Yuya, Osada Minoru, Tsuda Hiroyuki, Ishigure Takaaki, Toyofuku Takashi, Shimode Shinji, Imai Hiroaki

10 巻 ( 1 ) 頁： 2266 - 2266 2020年2月

Nitrogen doped ultrathin calcium/sodium niobate perovskite nanosheets for photocatalytic water oxidation 査読有り国際誌

Khan Muhammad Shuaib, Diao Zhidan, Osada Minoru, Shen Shaohua

SOLAR ENERGY MATERIALS AND SOLAR CELLS 205 巻 2020年2月

UV degradation mechanism of TiO2-based perovskite solar cells studied by pump-probe spectroscopy 査読有り国際誌

Luo Chih-Wei, Thilakan Anusha Puliparambil, Li Jia-Xin, Chen Tzu-Pei, Li Shao-Sian, Chen Chun-Wei, Yabushita Atsushi, Osada Minoru, Tsukagoshi Kazuhito, Sasaki Takayoshi

PHOTONICS FOR SOLAR ENERGY SYSTEMS VIII 11366 巻 2020年

無機ナノシートを利用した室温セラミックスコーティング

長田実

セラミックス 55 巻頁： 741 - 745 2020年

Tunable Chemical Coupling in Two-Dimensional van der Waals Electrostatic Heterostructures.

Taniguchi T, Li S, Nurdiwijayanto L, Kobayashi Y, Saito T, Miyata Y, Obata S, Saiki K, Yokoi H, Watanabe K, Taniguchi T, Tsukagoshi K, Ebina Y, Sasaki T, Osada M

ACS nano 2019年10月

Wafer-scale and deterministic patterned growth of monolayer MoS(2)via vapor-liquid-solid method

Li Shisheng, Lin Yung-Chang, Liu Xu-Ying, Hu Zehua, Wu Jing, Nakajima Hideaki, Liu Song, Okazaki Toshiya, Chen Wei, Minari Takeo, Sakuma Yoshiki, Tsukagoshi Kazuhito, Suenaga Kazu, Taniguchi Takaaki, Osada Minoru

NANOSCALE 11 巻 ( 34 ) 頁： 16122-16129 2019年9月

Dielectric nanosheet modified plasmonic-paper as highly sensitive and stable SERS substrate and its application for pesticides detection.

Mekonnen ML, Chen CH, Osada M, Su WN, Hwang BJ

Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy 225 巻頁： 117484 2019年8月

無機ナノシートの精密集積と高次メタマテリアルへの応用

長田実, 谷口貴章, 佐々木高義

表面技術 70 巻 ( 7 ) 頁： 355 - 358 2019年7月

Origin of Extended UV Stability of 2D Atomic Layer Titania-Based Perovskite Solar Cells Unveiled by Ultrafast Spectroscopy

Thilakan Anusha Puliparambil, Li Jia-Xing, Chen Tzu-Pei, Li Shao-Sian, Chen Chun-Wei, Osada Minoru, Tsukagoshi Kazuhito, Sasaki Takayoshi, Yabushita Atsushi, Wu Kaung-Hsiung, Luo Chih-Wei

ACS APPLIED MATERIALS & INTERFACES 11 巻 ( 24 ) 頁： 21473-21480 2019年6月

Enhanced oxide-ion conductivity of solid-state electrolyte mesocrystals

Tsukiyama Keishi, Takasaki Mihiro, Kitamura Naoto, Idemoto Yasushi, Oaki Yuya, Osada Minoru, Imai Hiroaki

NANOSCALE 11 巻 ( 10 ) 頁： 4523-4530 2019年3月

酸化物ナノシートの液相合成と機能材料への応用

長田実

ファインケミカル 48 巻頁： 28 - 33 2019年

Extra-Large Mechanical Anisotropy of a Hydrogel with Maximized Electrostatic Repulsion between Cofacially Aligned 2D Electrolytes 査読有り

Sano Koki, Arazoe Yuka Onuma, Ishida Yasuhiro, Ebina Yasuo, Osada Minoru, Sasaki Takayoshi, Hikima Takaaki, Aida Takuzo

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 57 巻 ( 38 ) 頁： 12508 - 12513 2018年9月

Extra‐Large Mechanical Anisotropy of a Hydrogel with Maximized Electrostatic Repulsion between Cofacially Aligned 2D Electrolytes

Koki Sano, Yuka Onuma Arazoe, Yasuhiro Ishida, Yasuo Ebina, Minoru Osada, Takayoshi Sasaki, Takaaki Hikima, Takuzo Aida

Angewandte Chemie 130 巻 ( 38 ) 頁： 12688 - 12693 2018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：Wiley

Abstract

In our previous work, we have shown that “electrostatic forces”, when generated anisotropically in aqueous media by 2D electrolytes upon cofacial orientation, enable the formation of a hydrogel with an anisotropic parameter, as defined by the ratio of elastic moduli E<sub>⊥</sub>/E<sub>∥</sub>, of 3.0. Herein, we successfully developed the design strategy for a hydrogel with an anisotropic parameter of no less than 85. This value is not only 28 times greater than that of our previous anisotropic hydrogel but also 6 times larger than the current champion record in synthetic hydrogels (E<sub>⊥</sub>/E<sub>∥</sub>∼15). Firstly, we simply lowered ionic contaminants in the hydrogel and were able to enhance the anisotropic parameter from 3.0 to 18. Then, we chose a supporting polymer network allowing the hydrogel to carry a higher interior permittivity. Consequently, the anisotropic parameter was further enhanced from 18 to 85. Owing to the enhanced mechanical anisotropy, our new hydrogel displayed a superb ability of seismic isolation.

DOI： 10.1002/ange.201807240

High areal capacitance and rate capability using filled Ni foam current collector 査読有り

Zheyin Yu, Zhenxiang Cheng, George Tsekouras, Xiaolin Wang, Xiangyang Kong, Minoru Osada, Shi Xue Dou

Electrochimica Acta 281 巻頁： 761 - 768 2018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：Elsevier Ltd

A novel approach to achieving high areal capacitance and rate capability is demonstrated, whereby an active material is loaded onto a high surface area, filled Ni foam current collector. Micro/nano Ni-filled Ni foam (MNFNF) current collector was fabricated by initially filling commercial Ni foam with Ni slurry and sintering to yield micro Ni-filled Ni foam, followed by electrochemical deposition of nano Ni. This current collector has a greatly enhanced surface area compared to Ni foam, allowing for high mass loading of active material and thereby high areal capacitance and rate capability. Using NiCo2O4 prepared via hydrothermal reaction followed by annealing as the active material, an outstanding areal capacitance of 29.4 F cm-2 at 5 mA cm−2 discharge was achieved, while a high 80% of this capacitance (i.e. 23.5 F cm−2) was retained at 50 mA cm−2 discharge, ascribed to the high surface area and high conductivity of the MNFNF current collector. Regarding stability, only a 2% decrease in areal capacitance after 1000 charge/discharge cycles was observed. The approach employed here might be used to enhance the performance of other active materials besides NiCo2O4.

DOI： 10.1016/j.electacta.2018.06.007

Multifield Control of Domains in a Room-Temperature Multiferroic 0.85BiTi0.1Fe0.8Mg0.1O3-0.15CaTiO3 Thin Film 査読有り

Tingting Jia, Ziran Fan, Junxiang Yao, Cong Liu, Yuhao Li, Junxi Yu, Bi Fu, Hongyang Zhao, Minoru Osada, Ehsan Nasr Esfahani, Yaodong Yang, Yuanxu Wang, Jiang-Yu Li, Hideo Kimura, Zhenxiang Cheng

ACS Applied Materials and Interfaces 10 巻 ( 24 ) 頁： 20712 - 20719 2018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：American Chemical Society

Single-phase materials that combine electric polarization and magnetization are promising for applications in multifunctional sensors, information storage, spintronic devices, etc. Following the idea of a percolating network of magnetic ions (e.g., Fe) with strong superexchange interactions within a structural scaffold with a polar lattice, a solid solution thin film with perovskite structure at a morphotropic phase boundary with a high level of Fe atoms on the B site of perovskite structure is deposited to combine both ferroelectric and ferromagnetic ordering at room temperature with magnetoelectric coupling. In this work, a 0.85BiTi0.1Fe0.8Mg0.1O3-0.15CaTiO3 thin film has been deposited by pulsed laser deposition (PLD). Both the ferroelectricity and the magnetism were characterized at room temperature. Large polarization and a large piezoelectric effective coefficient d33 were obtained. Multifield coupling of the thin film has been characterized by scanning force microscopy. Ferroelectric domains and magnetic domains could be switched by magnetic field (H), electric field (E), mechanical force (F), and, indicating that complex cross-coupling exists among the electric polarization, magnetic ordering and elastic deformation in 0.85BiTi0.1Fe0.8Mg0.1O3-0.15CaTiO3 thin film at room temperature. This work also shows the possibility of writing information with electric field, magnetic field, and mechanical force and then reading data by magnetic field. We expect that this work will benefit information applications.

DOI： 10.1021/acsami.8b05289

Vapour-liquid-solid growth of monolayer MoS<sub>2</sub> nanoribbons 査読有り

Li, SS; Lin, YC; Zhao, W; Wu, J; Wang, Z; Hu, ZH; Shen, YD; Tang, DM; Wang, JY; Zhang, Q; Zhu, H; Chu, LQ; Zhao, WJ; Liu, C; Sun, ZP; Taniguchi, T; Osada, M; Chen, W; Xu, QH; Wee, ATS; Suenaga, K; Ding, F; Eda, G

NATURE MATERIALS 17 巻 ( 6 ) 頁： 535 - + 2018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 Materials

Chemical vapour deposition of two-dimensional materials typically involves the conversion of vapour precursors to solid products in a vapour-solid-solid mode. Here, we report the vapour-liquid-solid growth of monolayer MoS2, yielding highly crystalline ribbons with a width of few tens to thousands of nanometres. This vapour-liquid-solid growth is triggered by the reaction between MoO3 and NaCl, which results in the formation of molten Na-Mo-O droplets. These droplets mediate the growth of MoS2 ribbons in the 'crawling mode' when saturated with sulfur. The locally well-defined orientations of the ribbons reveal the regular horizontal motion of the droplets during growth. Using atomic-resolution scanning transmission electron microscopy and second harmonic generation microscopy, we show that the ribbons are grown homoepitaxially on monolayer MoS2 with predominantly 2H- or 3R-type stacking. Our findings highlight the prospects for the controlled growth of atomically thin nanostructure arrays for nanoelectronic devices and the development of unique mixed-dimensional structures.

DOI： 10.1038/s41563-018-0055-z

Chemical synthesis of porous barium titanate thin film and thermal stabilization of ferroelectric phase by porosity-induced strain 査読有り

Norihiro Suzuki, Minoru Osada, Motasim Billah, Yoshio Bando, Yusuke Yamauchi, Shahriar A. Hossain

Journal of Visualized Experiments 2018 巻 ( 133 ) 2018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：Journal of Visualized Experiments

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 °C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications. In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

DOI： 10.3791/57441

Self-Sensitization and Photo-Polymerization of Diacetylene Molecules Self-Assembled on a Hexagonal-Boron Nitride Nanosheet 査読有り

Verveniotis, E; Okawa, Y; Watanabe, K; Taniguchi, T; Taniguchi, T; Osada, M; Joachim, C; Aono, M

POLYMERS 10 巻 ( 2 ) 2018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：Polymers

Long poly-diacetylene chains are excellent candidates for planar, on-surface synthesized molecular electronic wires. Since hexagonal-Boron Nitride (h-BN) was identified as the best available atomically flat insulator for the deposition of poly-diacetylene precursors, we demonstrate the polymerization patterns and rate on it under UV-light irradiation, with subsequent polymer identification by atomic force microscopy. The results on h-BN indicate self-sensitization which yields blocks comprised of several polymers, unlike on the well-studied graphite/diacetylene system, where the polymers are always isolated. In addition, the photo-polymerization proceeds at least 170 times faster on h-BN, where it also results in longer polymers. Both effects are explained by the h-BN bandgap, which is larger than the diacetylene electronic excitation energy, thus allowing the transfer of excess energy absorbed by polymerized wires to adjacent monomers, triggering their polymerization. This work sets the stage for conductance measurements of single molecular poly-diacetylene wires on h-BN.

DOI： 10.3390/polym10020206

Self-Assembly Atomic Stacking Transport Layer of 2D Layered Titania for Perovskite Solar Cells with Extended UV Stability 査読有り

Tzu-Pei Chen, Chung-Wei Lin, Shao-Sian Li, Yung-Han Tsai, Cheng-Yen Wen, Wendy Jessica Lin, Fei-Man Hsiao, Ya-Ping Chiu, Kazuhito Tsukagoshi, Minoru Osada, Takayoshi Sasaki, Chun-Wei Chen

Advanced Energy Materials 8 巻 ( 2 ) 2018年1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-VCH Verlag

A novel atomic stacking transporting layer (ASTL) based on 2D atomic sheets of titania (Ti1−δO2) is demonstrated in organic–inorganic lead halide perovskite solar cells. The atomically thin ASTL of 2D titania, which is fabricated using a solution-processed self-assembly atomic layer-by-layer deposition technique, exhibits the unique features of high UV transparency and negligible (or very low) oxygen vacancies, making it a promising electron transporting material in the development of stable and high-performance perovskite solar cells. In particular, the solution-processable atomically thin ASTL of 2D titania atomic sheets shows superior inhibition of UV degradation of perovskite solar cell devices, compared to the conventional high-temperature sintered TiO2 counterpart, which usually causes the notorious instability of devices under UV irradiation. The discovery opens up a new dimension to utilize the 2D layered materials with a great variety of homostructrual or heterostructural atomic stacking architectures to be integrated with the fabrication of large-area photovoltaic or optoelectronic devices based on the solution processes.

DOI： 10.1002/aenm.201701722

Nanoarchitectonics in dielectric/ferroelectric layered perovskites: From bulk 3D systems to 2D nanosheets 査読有り

Minoru Osada, Takayoshi Sasaki

Dalton Transactions 47 巻 ( 9 ) 頁： 2841 - 2851 2018年

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Royal Society of Chemistry

We present an overview of recent investigations on the dielectric/ferroelectric properties of Dion-Jacobson-type perovskites, including bulk 3D layered systems and their exfoliated 2D nanosheets. In contrast to the Ruddlesden-Popper and Aurivillius phases, the Dion-Jacobson phases in bulk 3D systems have not been important targets for constructing dielectric/ferroelectric materials. However, recent investigations on Dion-Jacobson phases have provided new impetus to dielectric/ferroelectric materials. Dion-Jacobson perovskites can also facilitate delamination into 2D nanosheets. Layer-by-layer engineering of 2D perovskite nanosheets has a great potential for the rational design of new high-k dielectric/ferroelectric materials and nanodevices.

DOI： 10.1039/c7dt03719h

Elucidation of structure and conduction mechanism in Nd-Mn substituted Y-type strontium hexaferrites 査読有り

Bashir Ahmad, Muhammad Naeem Ashiq, Muhammad Shuaib Khan, Minoru Osada, Muhammad Najam-Ul-Haq, Irshad Ali

JOURNAL OF ALLOYS AND COMPOUNDS 723 巻頁： 9 - 16 2017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：ELSEVIER SCIENCE SA

Technologically important ferrites magnetic materials with nominal composition "Sr2-xNdxCo2MnyFe12-yO22" (x = 0.0 to 0.1 and y = 0.0 to 1.0) were fabricated by the simple sol-gel method. The X-ray diffraction analysis endorsed the formation of well-defined Y-type hexagonal single phase with crys-tallite size in range of 38-45 nm. Owing to reduction of Fe3+ ions at octahedral site, an increase in DC resistivity was observed from 4.083 x 10(8) to 2.376 x 10(9) Omega-cm with the increase in substituents content. The two conduction mechanisms operating in ferri- and paramagnetic regions were shown by Arrhenius plot. It was observed that conduction in ferrimagnetic and paramagnetic regions was governed by the hopping of electrons and polarons, respectively. The decrease in Curie temperature "Tc" (553-423 K) was detected as a factor of Nd-Mn content due to decrease in Fe-Fe interaction at octahedral site. The changes in the values of dielectric constant (epsilon'), dielectric loss factor (epsilon") and tan loss (delta) follow Maxwell-Wagner model. The relatively high resistivity (2.376 x 10(9) Omega-cm) and low dielectric constants (2.97 at 1 MHz) for the sample with x = 0.1 and y = 1.0 make this material as an excellent candidates for high frequency microwave devices. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2017.06.219

Origin of thermally stable ferroelectricity in a porous barium titanate thin film synthesized through block copolymer templating(vol 5, 076111, 2017) 査読有り

Norihiro Suzuki, Minoru Osada, Motasim Billah, Zeid Abdullah Alothman, Yoshio Bando, Yusuke Yamauchi, Md. Shahriar A. Hossain

APL MATERIALS 5 巻 ( 9 ) 2017年9月

Layer-by-layer engineering of two-dimensional perovskite nanosheets for tailored microwave dielectrics 査読有り

Muhammad Shuaib Khan, Hyung-Jun Kim, Takaaki Taniguchi, Yasuo Ebina, Takayoshi Sasaki, Minoru Osada

APPLIED PHYSICS EXPRESS 10 巻 ( 9 ) 2017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：IOP PUBLISHING LTD

We report an approach for constructing ultrathin microwave dielectrics using two-dimensional (2D) perovskite nanosheets (Ca2Nb3O10). The solution-based layer-by-layer assembly of Ca2Nb3O10 nanosheets enables the tailoring of dielectric responses and breakdown voltage in order to realize miniaturized capacitors with improved performances. Multilayer stacked nanosheet films showed a stable dielectric response of up to 10 GHz; the dielectric constant of similar to 200 is the highest among high-k perovskites in the ultrathin region (< 30 nm). Moreover, the nanosheet films realized a high capacitance density (similar to 20 mu F/cm(2)) with a robust thermal stability up to 250 degrees C. These superior dielectric properties of perovskite nanosheets offer a new solution for high-performance microwave devices. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/APEX.10.091501

Photoreduction Dependent p- and n-Type Semiconducting Field-Effect Transistor Properties in Undoped Reduced Graphene Oxide 査読有り

Hiroshi Takehira, Md Saidul Islam, Mohammad Razaul Karim, Yuta Shudo, Ryo Ohtani, Leonard F. Lindoy, Takaaki Taniguchi, Minoru Osada, Shinya Hayami

CHEMISTRYSELECT 2 巻 ( 24 ) 頁： 6941 - 6944 2017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：WILEY-V C H VERLAG GMBH

Both p- and n-type field effect transistors (FET) properties have been observed in undoped reduced graphene oxide (rGO). Short and long time exposure of GO during photo reduction results in the formation of respective p- and n-type rGO semiconductor. Achieving duel behavior of this type in an undoped material is exceedingly unusual. Herein we report the presence of such behavior in the reduced from of graphene oxide (rGO) for the first time.

DOI： 10.1002/slct.201701509

Atomic Layer Engineering of High-kappa Ferroelectricity in 2D Perovskites 査読有り

Bao-Wen Li, Minoru Osada, Yoon-Hyun Kim, Yasuo Ebina, Kosho Akatsuka, Takayoshi Sasaki

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 139 巻 ( 31 ) 頁： 10868 - 10874 2017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 CHEMICAL SOC

Complex perovskite oxides offer tremendous potential for controlling their rich variety of electronic properties, including high-T-C superconductivity, high-kappa ferroelectricity, and quantum magnetism. Atomic-scale control of these intriguing properties in ultrathin perovskites is an important challenge for exploring new physics and device functionality at atomic dimensions. Here, we demonstrate atomic-scale engineering of dielectric responses using two-dimensional (2D) homologous perovskite nanosheets (Ca2Nam-3NbmO3m+1; m = 3-6). In this homologous 2D material, the thickness of the perovskite layers can be incrementally controlled by changing m, and such atomic layer engineering enhances the high-kappa dielectric response and local ferroelectric instability. The end member (m = 6) attains a high dielectric constant of similar to 470, which is the highest among all known dielectrics in the ultrathin region (<10 nm). These results provide a new strategy for achieving high-kappa ferroelectrics for use in ultrascaled high-density capacitors and post-graphene technology.

DOI： 10.1021/jacs.7b05665

Origin of thermally stable ferroelectricity in a porous barium titanate thin film synthesized through block copolymer templating 査読有り

Norihiro Suzuki, Minoru Osada, Motasim Billah, Zeid Abdullah Alothman, Yoshio Bando, Yusuke Yamauchi, Md. Shahriar A. Hossain

APL MATERIALS 5 巻 ( 7 ) 2017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 porous barium titanate (BaTiO3) thin film was chemically synthesized using a surfactant-assisted sol-gel method in which micelles of amphipathic diblock copolymers served as structure-directing agents. In the Raman spectrum of the porous BaTiO3 thin film, a peak corresponding to the ferroelectric tetragonal phase was observed at around 710 cm(-1), and it remained stable at much higher temperature than the Curie temperature of bulk single-crystal BaTiO3 (similar to 130 degrees C). Measurements revealed that the ferroelectricity of the BaTiO3 thin film has high thermal stability. By analyzing high-resolution transmission electron microscope images of the BaTiO3 thin film by the fast Fourier transform mapping method, the spatial distribution of stress in the BaTiO3 framework was clearly visualized. Careful analysis also indicated that the porosity in the BaTiO3 thin film introduced anisotropic compressive stress, which deformed the crystals. The resulting elongated unit cell caused further displacement of the Ti4+ cation from the center of the lattice. This displacement increased the electric dipole moment of the BaTiO3 thin film, effectively enhancing its ferro(piezo) electricity. (C) 2017 Author(s).

DOI： 10.1063/1.4995650

High-temperature dielectric responses in all-nanosheet capacitors 査読有り

Muhammad Shuaib Khan, Minoru Osada, Hyung-Jun Kim, Yasuo Ebina, Wataru Sugimoto, Takayoshi Sasaki

Japanese Journal of Applied Physics 56 巻 ( 6 ) 2017年6月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Japan Society of Applied Physics

We have investigated high-temperature dielectric responses of layer-by-layer assembled nanosheet capacitors. All-nanosheet capacitors are fabricated by stacking metallic Ru0.95O2 as electrodes and dielectric Ca2Nb3O10 nanosheets as insulators. Through in situ characterizations, we find that all-nanosheet capacitors exhibit a size-free high-k dielectric response (&gt
155) and a moderate insulation resistance (&gt
1 ' 10%5A/cm2) at high temperatures up to 200 °C. The concomitant presence of high ϵr, low leakage profile, and thermal stability in high-k nanocapacitors is critically important for application in high-temperature electronics.

DOI： 10.7567/JJAP.56.06GH09

Neat monolayer tiling of molecularly thin two-dimensional materials in 1 min 査読有り

Kazuaki Matsuba, Chengxiang Wang, Kazuko Saruwatari, Yusuke Uesusuki, Kosho Akatsuka, Minoru Osada, Yasuo Ebina, Renzhi Ma, Takayoshi Sasaki

SCIENCE ADVANCES 3 巻 ( 6 ) 2017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 ASSOC ADVANCEMENT SCIENCE

Controlled arrangement of molecularly thin two-dimensional (2D) materials on a substrate, particularly into precisely organized mono-andmultilayer structures, is a key to design a nanodevice using their unique and enhanced physical properties. Several techniques such as mechanical transfer process and Langmuir-Blodgett deposition have been applied for this purpose, but they have severe restrictions for large-scale practical applications, for example, limited processable area and long fabrication time, requiring skilled multistep operations. We report a facile one-pot spin-coating method to realize dense monolayer tiling of various 2D materials, such as graphene and metal oxide nanosheets, within 1 min over a wide area (for example, a 30-mmf substrate). Centrifugal force drives the nanosheets in a thin fluid layer to the substrate edgewhere they are packed edge to edge all the way to the central region, without forming overlaps. We investigated the relationship between precursor concentration, rotation speed, and ultraviolet-visible absorbance and developed an effective method to optimize the parameters for neat monolayer films. The multilayer buildup is feasible by repeating the spin-coating process combined with a heat treatment at moderate temperature. This versatile solution-based technique will provide both fundamental and practical advancements in the rapid large-scale production of artificial lattice-like films and nanodevices based on 2D materials.

DOI： 10.1126/sciadv.1700414

Ferroelectric BaTiO3 dipole induced charge transfer enhancement in dye-sensitized solar cells 査読有り

Keyuan Feng, Xiaoyan Liu, Donghui Si, Xiao Tang, An Xing, Minoru Osada, Peng Xiao

JOURNAL OF POWER SOURCES 350 巻頁： 35 - 40 2017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

BaTiO3/TiO2 nanocomposite films with varied amount of BaTiO3 are fabricated and applied as photo anodes for dye-sensitized solar cells (DSCs) and demonstrated enhanced power conversion efficiency. Ferroelectricity of BaTiO3 in the film after subjected to a annealing process up to 450 degrees C is examined by Switching Spectroscopy Piezoresponse Force Microscopy (SSPFM). The highest performance is achieved in 1.0 wt% BaTiO3 addition as a result of increased photocurrent density (J(sc)) and fill factor (FF), regardless of reduction of dye-loading. Electrochemical impedance spectroscopy (EIS) measurements at different bias voltages (<= Voc) in dark suggest that ferroelectric dipole induced electric field has positive effects on enhancing electron mobility and suppressing charge recombination. Although more detailed experiments are needed in designing of the nanocomposite films for compensating characteristics of dye-loading and electron mobility, introduction of ferroelectric dipole induced electric field into the photoanode would be a good strategy in achieving further improvement of power conversion efficiency of DSCs through improved charge transfer properties. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2017.03.049

Mechanical force involved multiple fields switching of both local ferroelectric and magnetic domain in a Bi5Ti3FeO15 thin film 査読有り

Tingting Jia, Hideo Kimura, Zhenxiang Cheng, Hongyang Zhao, Yoon-Hyun Kim, Minoru Osada, Takao Matsumoto, Naoya Shibata, Yuichi Ikuhara

NPG ASIA MATERIALS 9 巻 2017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

Multiferroics have received intense attention due to their great application potential in multi-state information storage devices and new types of sensors. Coupling among ferroic orders such as ferroelectricity, (anti-) ferromagnetism, ferroelasticity and so on will enable dynamic interaction between these ordering parameters. Direct visualization of such coupling behavior in single-phase multiferroic materials is highly desirable for both applications and fundamental study. Manipulation of both ferroelectric and magnetic domains of Bi5Ti3FeO15 thin film using electric field and external mechanical force is reported, which confirms the magnetoelectric coupling in Bi5Ti3FeO15, indicates the electric and magnetic orders are coupled through ferroelasticity. Due to the anisotropic relaxation of ferroelastic strain, the back-switching of out-of-plane electric domains is not as obvious as in-plane. An inevitable destabilization of the coupling between elastic and magnetic ordering happens because of the elastic strain relaxation, which result in a subsequent decay of magnetic domain switching. Mechanical force applied on the surface of Bi5Ti3FeO15 film generates by an atomic force microscopy tip will effectively drive a transition of the local ferroelastic strain state, reverse both the polarization and magnetization in a way similar to an electric field. Current work provides a framework for exploring cross-coupling among multiple orders and potential for developing novel nanoscale functional devices.

DOI： 10.1038/am.2017.3

Atomic layer engineering of high-k ferroelectricity in 2D perovskites 査読有り

139 巻頁： 10868-10874 2017年

Ferroelectric-assisted gold nanoparticles array for centimeter-scale highly reproducible SERS substrates

X. Liu, M. Osada, K. Kitamura, T. Nagata, D. Si

Scientific Reports 7 巻頁： 3630 2017年

Neat monolayer tiling of molecularly thin two-dimensional materials in one minute 査読有り

3 巻頁： e1700414 2017年

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

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

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

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

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

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

Gigantic plasmon resonance effects on magneto-optical activity of molecularly thin ferromagnets near gold surfaces 査読有り

Minoru Osada, Natália Hajduková-Šmídová, Kosho Akatsuka, Satoshi Yoguchi, Takayoshi Sasaki

Journal of Materials Chemistry C 1 巻 ( 14 ) 頁： 2520 - 2524 2013年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report on a new magneto-plasmonic material consisting of 1 nm thick ferromagnetic nanosheets and Au nanoparticles. The magneto-optical (MO) Kerr spectra of Ti0.8Co0.2O2 nanosheets near Au surfaces showed a gigantic MO response (∼106 deg cm-1) in the visible wavelength region (380-600 nm), not present in Ti 0.8Co0.2O2 nanosheets on a bare glass substrate. The observed peaks correspond to intrinsic d-d* electronic transitions in Ti0.8Co0.2O2 and are consistent with the near-field enhancement of the MO response resulting from the spectral overlap of the surface-plasmon-resonance (SPR) in the Au surface with the electronic transitions in Ti0.8Co0.2O2. Similar SPR effects were also achieved in ferromagnetic nanosheet/Au with different compositions and with different separation distances (&lt
5 nm). This demonstration of SPR-enhanced magneto-optics in the ferromagnetic/plasmonic nanosystem may enable designing of nanoarchitectures for miniaturized high-performance MO devices and for remote sensing and imaging of magnetic fields. © The Royal Society of Chemistry 2013.

DOI： 10.1039/c3tc00952a

Synthesis of Highly Strained Mesostructured SrTiO3/BaTiO3 Composite Films with Robust Ferroelectricity 査読有り

Norihiro Suzuki, Mohamed B. Zakaria, Nagy L. Torad, Kevin C-W Wu, Yoshihiro Nemoto, Masataka Imura, Minoru Osada, Yusuke Yamauchi

CHEMISTRY-A EUROPEAN JOURNAL 19 巻 ( 14 ) 頁： 4446 - 4450 2013年4月

Fabrication of Ruthenium Metal Nanosheets via Topotactic Metallization of Exfoliated Ruthenate Nanosheets 査読有り

Katsutoshi Fukuda, Jun Sato, Takahiro Saida, Wataru Sugimoto, Yasuo Ebina, Tatsuo Shibata, Minoru Osada, Takayoshi Sasaki

INORGANIC CHEMISTRY 52 巻 ( 5 ) 頁： 2280 - 2282 2013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：AMER CHEMICAL SOC

The metallization behavior of molecularly thin RuO2 nanosheets obtained from complete delamination of layered ruthenates was studied. Interestingly, the RuO2 nanosheets in a monolayer state topotactically transformed into a single layer of Ru atoms, i.e., ruthenium metal nanosheets, which can be regarded as a new family of nanosized metals.

DOI： 10.1021/ic302720d

Low-frequency Raman scattering in binary silicate glass: Boson peak frequency and its general expression 査読有り

Kensaku Nakamura, Yoshihiro Takahashi, Minoru Osada, Takumi Fujiwara

Journal of the Ceramic Society of Japan 121 巻 ( 1420 ) 頁： 1012 - 1014 2013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：Ceramic Society of Japan

Low-frequency Raman measurement was performed in alkali and alkaline-earth silicate glasses to elucidate the effect of introduction of network modifiers on boson peak nature. Our study illustrated that introduction of small/medium ions tended to increase in the boson peak frequency (ωBP), whereas the introduction of large ions tended to decrease the frequency. Although ωBP has been suggested to be proportional to the shear modulus, no linear relationship was obtained in these binary systems. Instead, we experimentally demonstrated that mean atomic volume can explain variations in ωBP regardless of the trend of boson peaks. © 2013 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.121.1012

Room temperature multiferroic heterostructure: Nd: BiFeO3/YMnO3 査読有り

Hongyang Zhao, Hideo Kimura, Zhenxiang Cheng, Xiaolin Wang, Qiwen Yao, Minoru Osada, Baowen Li

Journal of Crystal Growth 365 巻頁： 19 - 23 2013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：Elsevier B.V.

In order to search candidate multiferroics, a heterostructure of Nd:BiFeO3/YMnO3 (BFO/YMO) was designed. It was fabricated using a pulsed laser deposition (PLD) method on (111) Nb: SrTiO3 substrate through layer-by-layer growth. The particularly interesting phases for Nd:BiFeO3 (P4mm) and YMnO3 (hexagonal and orthorhombic) were observed. This film has a high ferromagnetic Curie temperature at 420 K. The ferroelectric domain switching was observed and it exhibited large electromechanical coupling with maximum d33∼73 pm/V at 10 V. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2012.12.023

Structural relaxation and quasi-elastic light scattering in glass: Approach by ferroelectric and ion-conducting phases 査読有り

Yoshihiro Takahashi, Kensaku Nakamura, Minoru Osada, Takumi Fujiwara

SCIENTIFIC REPORTS 2 巻 2012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

Inelastic light scattering has been utilized for examining the structure of glass and its relaxation. However, the quasi-elastic-light-scattering (QLS) phenomenon has not been addressed in much detail. In this study, we observed pronounced QLS-intensity variations in two temperature domains-supercooled liquid (SCL) state (alpha-relaxation regime) and below the glass-transition temperature (beta-relaxation regime)-in niobium-oxide (Nb2O5)-rich glass. These variations may be interpreted on the basis of the concept of ferroelectric and ion-conducting phases. It was suggested that the observed QLS originates as a result of the polarization fluctuation of NbO6 units, which is due to the dynamics of the nanometric phase separation in the SCL phase (alpha-regime), and the fluctuation due to the migration/hopping of conductible ions that are localized in the vicinity of the NbO6 units (beta-regime).

DOI： 10.1038/srep00714

The formation of graphene-titania hybrid films and their resistance change under ultraviolet irradiation 査読有り

Pengzhan Sun, Renzhi Ma, Minoru Osada, Takayoshi Sasaki, Jinquan Wei, Kunlin Wang, Dehai Wu, Yao Cheng, Hongwei Zhu

CARBON 50 巻 ( 12 ) 頁： 4518 - 4523 2012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：PERGAMON-ELSEVIER SCIENCE LTD

We report the fabrication of hybrid films of graphene and monolayer titania using a simple electrostatic self-assembly method. Ultraviolet (UV) responses of the hybrid films based on the graphene-titania structure were investigated. We observed that the resistance of the graphene-titania hybrid increased exponentially with UV irradiation time and decreased exponentially when UV was turned off. Time constants of the order of hundreds of seconds were identified and found to be sensitive to the gas environment of graphene. The UV response as well as the time constant is tunable by varying the number of titania layers. Our results confirmed that UV irradiation played a significant role in the resistance modulation of graphene as well as graphene-titania hybrid films. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2012.05.035

Interfacial phenomena in solid-state lithium battery with sulfide solid electrolyte 査読有り

Kazunori Takada, Narumi Ohta, Lianqi Zhang, Xiaoxiong Xu, Bui Thi Hang, Tsuyoshi Ohnishi, Minoru Osada, Takayoshi Sasaki

SOLID STATE IONICS 225 巻頁： 594 - 597 2012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：ELSEVIER SCIENCE BV

The effects of surface coating on electrode properties of LiMn2O4 in a sulfide solid electrolyte were investigated. The surface coating with LiNbO3 reduced the electrode resistance by two orders of magnitude. Changes in the electrode properties were very similar to those observed for the corresponding LiCoO2 electrodes, which strongly suggest that the space-charge layer formed at the high-voltage cathode/sulfide electrolyte interface is rate-determining and must be controlled to improve the rate capability. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2012.01.009

Nano-Materials Design for High-TC Ferromagnets of Ti1-xCoxO2 Nanosheets 査読有り

Minoru Osada, Takayoshi Sasaki, Kanta Ono

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY 9 巻 ( 5 ) 頁： 936 - 941 2012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-BLACKWELL

We present materials design of high-TC ferromagnetic nanomaterials based on first-principles calculations. Two-dimensional (2D) titania nanosheet, a recently discovered room-temperature (RT) ferromagnetic nanomaterial, is an important target for 2D ferromagnets. In Ti1-xCoxO2 nanosheets with Co2+ oxidation state, the ferromagnetic states are highly stabilized up to x=0.5 with a modest doping dependence of magnetic moment (1 mu B/Co). Moreover, we find that tailoring properties could be achieved by tuning Co oxidation states, and the optimally doped Ti1-xCoxO2 nanosheets (Co3+; x=0.125, 0.25) are found to be an excellent RT half-metallic ferromagnet with a large magnetic moment (similar to 4 mu B/Co). 2D nanosheet is therefore expected to provide a very useful platform for nanoscale spinelectronics devices.

DOI： 10.1111/j.1744-7402.2012.02783.x

Percolative BaTiO3/Carbon-Nanotube Composite Films Employing Aerosol Deposition 査読有り

Yoon-Hyun Kim, Minoru Osada, Hong-Ki Kim, Song-Min Nam

JAPANESE JOURNAL OF APPLIED PHYSICS 51 巻 ( 9 ) 2012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：IOP PUBLISHING LTD

Percolative BaTiO3/multiwalled carbon nanotube (MWNT) composite thick films were developed using an aerosol deposition (AD) process at room temperature. Well-dispersed mixed powders with various volume ratios were utilized as the starting powders for AD, and dense BaTiO3/MWNT composite thick films were successfully fabricated with the starting mixed powders with 0.01 vol% MWNTs. The existence of MWNTs in the composite films was confirmed using Raman spectroscopy. The composite films show a high relative dielectric constant (657 at 1 kHz), which is approximately 7 times larger than that (91 at 1 kHz) of the BaTiO3 films. In addition, the strong frequency dispersion of the dielectric constant in the low-frequency range was confirmed for the composite films. The dielectric properties of the composite films were investigated using the dielectric mechanism used in percolative composites. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.09LC07

SE(R)RS excitation profile of free-base 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin on immobilized gold nanoparticles 査読有り

Natalia Hajdukova-Smidova, Marek Prochazka, Minoru Osada

VIBRATIONAL SPECTROSCOPY 62 巻頁： 115 - 120 2012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

Surface-enhanced (resonance) Raman scattering - SE(R)RS - excitation profile (dependence of SE(R)RS intensity on excitation wavelength) is a key point for optimizing of electromagnetic enhancement of particular SE(R)RS system. In this paper, we measured SE(R)RS excitation profile of free-base 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (TMPyP) on immobilized Au nanoparticles using confocal Raman microspectrometer with six excitation wavelengths (457.9, 488.0, 514.5, 530.9, 568.2 and 647.1 nm). Au colloidal nanoparticles were immobilized to a glass slide via a self-assembled monolayer of 3-aminopropyltrimethoxysilane. SE(R)RS excitation profile is correlated with the corresponding surface plasmon extinction (SPE) spectrum of immobilized Au nanoparticles although the maximum of SE(R)RS intensity is slightly shifted from maximum of SPE. In our case of resonant molecule, SE(R)RS enhancement is coupled with molecular resonance enhancement and SE(R)RS excitation profile for particular vibrational mode depends on its TMPyP molecular resonance contribution. SE(R)RS excitation profile shows that maximal SE(R)RS intensity is obtained for 568.2 nm excitation that provides limit of detection (LOD) of TMPyP 2 x 10(-8) M in soaking solution. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.vibspec.2012.04.007

RbBiNb2O7: A New Lead-Free High-T-c Ferroelectric 査読有り

Bao-Wen Li, Minoru Osada, Tadashi C. Ozawa, Takayoshi Sasaki

CHEMISTRY OF MATERIALS 24 巻 ( 16 ) 頁： 3111 - 3113 2012年8月

酸化物ナノシートを用いた機能性セラミックスコーティング

長田実, 佐々木高義, 佐々木高義, 佐々木高義

スマートプロセス学会誌 = Journal of smart processing 1 巻 ( 4 ) 頁： 150 - 154 2012年7月

NANOCRYSTALLIZATION AND OPTICAL PROPERTY OF WILLEMITE-TYPE SEMICONDUCTIVE Zn2GeO4 IN GLASS 査読有り

Yoshihiro Takahashi, Masataka Ando, Rie Ihara, Takumi Fujiwara, Minoru Osada

FUNCTIONAL MATERIALS LETTERS 5 巻 ( 2 ) 2012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：WORLD SCIENTIFIC PUBL CO PTE LTD

A wide band-gap semiconductive oxide Zn2GeO4 has recently attracted considerable interest because it is a multifunctional material; excellent photoluminescent (PL) and photocatalytic property, high-capacity anode for lithium batteries, and so on. Recently, present authors' group have fabricated transparent Zn2GeO4-nanocrystallized glass from a lithium zincogermanate glass. This article briefly describes a series of our studies on the nanocrystallized glass. Particularly, the phase-formation dynamics in supercooled-liquid phase and PL property of nanocrystallized glasses are presented.

DOI： 10.1142/S1793604712600089

Effect of annealing at maximum nucleation temperature on boson peak in lithium-disilicate glass 査読有り

Kensaku Nakamura, Yoshihiro Takahashi, Minoru Osada, Rie Ihara, Takumi Fujiwara

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 120 巻 ( 1402 ) 頁： 256 - 258 2012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：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

Low-frequency Raman scattering and TEM observations were conducted in 1Li(2)O-2SiO(2) glass subjected to annealing at maximum homogeneous nucleation temperature (similar to 460 degrees C) to elucidate the annealing effect on Boson-peak behavior and its relation to the structural evolution in nanoscale. It is suggested that the 1Li(2)O-2SiO(2) glass possesses a successive medium-range ordering through phase separation, and the Boson-peak frequency was largely affected by the ordering/phase-separation. (C) 2012 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.120.256

Photochromogenic Nanosheet Crystallites of Tungstate with a 2D Bronze Structure 査読有り

Katsutoshi Fukuda, Kosho Akatsuka, Yasuo Ebina, Minoru Osada, Wataru Sugimoto, Mutsumi Kimura, Takayoshi Sasaki

INORGANIC CHEMISTRY 51 巻 ( 3 ) 頁： 1540 - 1543 2012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：AMER CHEMICAL SOC

Layered rubidium tungstate, Rb4W11O35, with a two-dimensional (2D) bronze-type tunnel structure was successfully delaminated into colloidal nanosheets via a soft-chemical process involving acid exchange and subsequent intercalation of tetrabutylammonium ions. Characterizations by transmission electron microscopy and atomic force microscopy confirmed the formation of unilamellar 2D nanosheet crystallites with a unique thickness of similar to 3 nm and an average lateral size of 400 nm. The obtained nanosheets exhibited reversible color change upon UV-light excitation via an optical band gap of 3.5 eV. The ultimate 2D aspect ratio favorable for an adsorption of charge-compensating cations to trapped electrons working as a color center is presumably responsible for highly efficient photochromic behavior. Its coloration mainly consists of a broad band at a wavelength of 1800 nm and longer, which is much different from that of the common tungstate nanomaterials. Thus, the chromogenic nanosheet obtained in this study features the intense UV absorption and optically switchable visible-to-IR absorption, which may be useful for window applications such as cutoff filters and heat-absorbing films.

DOI： 10.1021/ic201834y

Soft-phonon mode observation in Li2Ge4O9 phase above room temperature 査読有り

Yoshihiro Takahashi, Jun Kunitomo, Kensaku Nakamura, Minoru Osada, Takumi Fujiwara

APPLIED PHYSICS LETTERS 100 巻 ( 9 ) 2012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：AMER INST PHYSICS

Li2Ge4O9 is known to be a ferroelectric phase with Curie temperature at T-c similar to -93 degrees C. In this study, we found both the lowest-frequency phonon and heat-capacity anomalies around 100 degrees C in the Li2Ge4O9 phase, demonstrating their presence in the structural phase-transition. The phase transition is probably triggered by regularization of distorted GeO6 octahedra in the paraelectric phase, resulting in another phase consisting of the regular octahedral GeO6 unit, which was supported by in situ measurement of emission of E-2 -> (4)A(2) transition in the Mn4+-doped phase. It is deduced that the phase transition is more dynamic than ferroelectric phase-transition originating in ordering of the Li ions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3688603]

DOI： 10.1063/1.3688603

Two-Dimensional Dielectric Nanosheets: Novel Nanoelectronics From Nanocrystal Building Blocks 査読有り

Minoru Osada, Takayoshi Sasaki

ADVANCED MATERIALS 24 巻 ( 2 ) 頁： 210 - 228 2012年1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

Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics.

DOI： 10.1002/adma.201103241

A- and B-Site Modified Perovskite Nanosheets and Their Integrations into High-k Dielectric Thin Films 査読有り

Minoru Osada, Takayoshi Sasaki

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY 9 巻 ( 1 ) 頁： 29 - 36 2012年1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-BLACKWELL

We investigated dielectric properties of perovskite nanosheets with different compositions (Ca2-xSrxNb3-yTayO10) to study the influence of A- and B-site modifications on dielectric properties. LangmuirBlodgett deposition was employed to fabricate multilayer nanofilms of perovskite nanosheets. In these nanosheets, the A-site modification by Sr2+ ions causes the increase in epsilon(r) value, whereas the B-site modification with Ta5+ ions improves leakage current characteristics and reduces permittivity value. The optimized property (epsilon(r) = 240) is obtained for Sr2Nb3O10 nanosheet. We also discuss high-kappa properties of Ca2-xSrxNb3-yTayO10 nanosheets by detailed investigations on first-principles calculations and interfacial structures.

DOI： 10.1111/j.1744-7402.2011.02713.x

Two-dimensional dielectric nanosheets: novel nanoelectronics from building blocks 招待有り査読有り

M. Osada, T. Sasaki

Adv. Mater. 24 巻頁： 210-228 2012年

Solution-Based Fabrication of Perovskite Multilayers and Superlattices Using Nanosheet Process 査読有り

Bao-Wen Li, Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Tadashi C. Ozawa, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS 50 巻 ( 9 ) 2011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：IOP PUBLISHING LTD

We report a solution-based fabrication of perovskite multilayers and superlattices using perovskite nanosheets. Perovskite nanosheets (LaNb2O7, Ca2Nb3O10, and Sr2Nb3O10) were prepared by delaminating layered perovskites. A layer-by-layer approach using Langmuir-Blodgett deposition was effective for fabricating high-quality nanofilms of perovskite nanosheets on various substrates, such as quartz glass, Si, and SrRuO3. Structural characterizations by X-ray diffraction, transmission electron microscopy, and hard X-ray photoelectron spectroscopy revealed that these perovskite nanofilms are composed of a well-ordered lamellar structure with an atomically sharp interface. The multilayer films exhibited a stable dielectric response inherent to the perovskite nanosheet. We also found that the superlattices of (LaNb2O7/Ca2Nb3O10)(5) and (Sr2Nb3O10/Ca2Nb3O10)(5) possess strong interface coupling, which gives rise to enhanced dielectric constant. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.09NA10

Controlled Polarizability of One-Nanometer-Thick Oxide Nanosheets for Tailored, High-kappa Nanodielectrics 査読有り

Minoru Osada, Genki Takanashi, Bao-Wen Li, Kosho Akatsuka, Yasuo Ebina, Kanta Ono, Hiroshi Funakubo, Kazunori Takada, Takayoshi Sasaki

ADVANCED FUNCTIONAL MATERIALS 21 巻 ( 18 ) 頁： 3482 - 3487 2011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-BLACKWELL

An important challenge in current microelectronics research is the development of techniques for making smaller, higher-performance electronic components. In this context, the fabrication and integration of ultrathin high-kappa dielectrics with good insulating properties is an important issue. Here, we report on a rational approach to produce high-performance nanodielectrics using one-nanometer-thick oxide nanosheets as a building block. In titano niobate nanosheets (TiNbO(5), Ti(2)NbO(7), Ti(5)NbO(14)), the octahedral distortion inherent to site-engineering by Nb incorporation results in a giant molecular polarizability, and their multilayer nanofilms exhibit a high dielectric constant (160-320), the largest value seen so far in high-kappa nanofilms with thickness down to 10 nm. Furthermore, these superior high-kappa properties are fairly temperature-independent with low leakage-current density (< 10(-7) A cm(-2)). This work may provide a new recipe for designing nanodielectrics desirable for practical high-kappa devices.

DOI： 10.1002/adfm.201100580

Nanoscale Characterization of Domain Structures in Bi4Ti3O12 Single Crystals Using Near-Field Raman Spectroscopy 査読有り

Claudia Carmignano, Minoru Osada, Yuji Noguchi, Yuuki Kitanaka, Masaru Miyayama

JAPANESE JOURNAL OF APPLIED PHYSICS 50 巻 ( 9 ) 2011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：JAPAN SOC APPLIED PHYSICS

We have investigated domain structures in Bi4Ti3O12 (BiT) single crystals by Raman scattering using scanning near-field optical microscopy (SNOM). In SNOM-Raman spectra, the polarization dependence reflects domain structures, and the spectra at the domain-wall region exhibit the splitting of the TiO6 mode at similar to 840 cm(-1) with the appearance of additional peaks, the behavior of which is different from that observed in the single-domain region. From the resonant Raman spectra of highly deficient BiT single crystals, we find that the resonance is localized at oxygen vacancies in TiO6 octahedra, and planer defects, owing to oxygen vacancies, accumulate near the domain walls, causing a strong domain pinning. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.09NE10

High-Energy Shift of Boson Peak and Its Broadening in Crystallization Regime: A Qualitative Aspect 査読有り

Yoshihiro Takahashi, Minoru Osada, Rie Ihara, Takumi Fujiwara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 巻 ( 9 ) 2011年9月

Nano-patterning of a TiO2-organic hybrid material using interference of surface plasmon on aluminum 査読有り

Hiroyo Segawa, Satoru Inoue, Minoru Osada, Yoshihiko Takeda

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 221 巻 ( 2-3 ) 頁： 232 - 238 2011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：ELSEVIER SCIENCE SA

Nano patterns of a TiO2-organic hybrid material have been fabricated by interference of surface plasmon on aluminum. The TiO2-organic hybrid materials were prepared by the sol-gel method, and were irradiated through an aluminum mask by a UV light. After the unreacted parts were removed, patterns were obtained on the films. The patterns of lines approximately 300 nm in width and with a sub-100-nm height were obtained by controlling the UV irradiation time. It was confirmed that the patterns changed to anatase patterns by sintering at temperatures above 450 degrees C. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2011.02.019

Low-frequency inelastic light scattering of zincogermanate glass in supercooledliquid regime 査読有り

Yoshihiro Takahashi, Minoru Osada, Masataka Ando, Rie Ihara, Takumi Fujiwara

JOURNAL OF APPLIED PHYSICS 109 巻 ( 12 ) 2011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 INST PHYSICS

We performed in situ observation of low-frequency inelastic light scattering in a zincogermanate glass showing nanocrystallization of semiconductive Zn(2)GeO(4) to elucidate the crystallization and phase transformation dynamics. In supercooledliquid state, an anomalous damping behavior of Boson peak was observed as the elastic softening happened. Combination of Boson and TEM studies revealed that the Boson damping is due to the liquid-liquid phase separation, which occurs prior to nanocrystallization, suggesting possibility of in situ spectroscopic observation of phase separation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3602085]

DOI： 10.1063/1.3602085

In situ Observation of Supercooled Liquid-Crystal Phase Transition in Glassy Ferroelectric LaBGeO5 査読有り

Yoshihiro Takahashi, Tomomichi Yasuoka, Minoru Osada, Rie Ihara, Takumi Fujiwara

JAPANESE JOURNAL OF APPLIED PHYSICS 50 巻 ( 6 ) 2011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：JAPAN SOC APPLIED PHYSICS

Inelastic light scattering was observed in situ from glassy ferroelectric LaBGeO5, which crystallizes the stillwellite-type stoichiometric phase, in the glass-supercooled liquid (SCL) and subsequent SCL-crystal phase transition regimes. The dynamics of the planar BO3 unit in the crystal growth period of the crystallization process was clarified through in situ observation. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.068002

Orbital reconstruction and interface ferromagnetism in self-assembled nanosheet superlattices 査読有り

M. Osada, T. Sasaki, K. Ono, Y. Kotani, S. Ueda, K. Kobayashi

ACS Nano 5 巻頁： 6871-6879 2011年

Tantalum oxide nanomesh as self-standing one nanometre thick electrolyte 査読有り

X. Xu, K. Takada, Katsutoshi Fukuda, T. Ohnishi, K. Aakatsuka, M. Osada, B. Hang, K. Kamagai, T. Sekiguchi, T. Sasaki

Energy. Environ. Sci. 4 巻頁： 3509-3512 2011年

Controlled polarizability of one-nanometer-thick oxide nanosheets for tailored, high-k nanodielectrics 査読有り

M. Osada, G. Takanashi, B. W. Li, K. Akatsuka, Y. Ebina, K. Ono, H. Funakubo, K. Takada, T. Sasaki

Adv. Funct. Mater. 21 巻頁： 3482-3487 2011年

Crystallization and Morphology of Glassy Sanbornite 査読有り

Yoshihiro Takahashi, Rie Ihara, Takumi Fujiwara, Minoru Osada

ELECTROCERAMICS IN JAPAN XIV 485 巻頁： 301 - + 2011年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：TRANS TECH PUBLICATIONS LTD

We investigated the crystallization and resulting morphology of a stoichiometric barium-silicate glass 1BaO-2SiO(2) (glassy sanbornite) by using transmission electron microscope and Raman spectroscopy. A crystalline aggregate structure consisting of a Ba5Si8O21 phase (trunk) and a beta-BaSi2O5 phase (branch) was observed in the heat-treated glassy sanbornite. The Ba-richer phase of Ba5Si8O21 precipitated prior to the formation of the stoichiometric beta-BaSi2O5 phase, suggesting the presence of the region in which the Ba ions are enriched or cohesively distributed. A considerable structural similarity between the glassy sanbornite and the Ba5Si8O21 phase was also suggested in this study.

DOI： 10.4028/www.scientific.net/KEM.485.301

Self-Assembled Nanofilm of Monodisperse Cobalt Hydroxide Hexagonal Platelets: Topotactic Conversion into Oxide and Resistive Switching 査読有り

Renzhi Ma, Minoru Osada, Linfeng Hu, Takayoshi Sasaki

CHEMISTRY OF MATERIALS 22 巻 ( 23 ) 頁： 6341 - 6346 2010年12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

The current work develops a solution-based self-assembling route to construct close-packed nanofilms (thickness approximate to 30 nm) using monodisperse hexagonal platelets of Co(OH)(2) as two-dimensional building blocks. The hydroxide film was postannealed and could be transformed into [111]-oriented cobalt monoxide (CoO) in a topotactic fashion retaining the original hexagonal platelet shape. Electrical resistive switching property of as-transformed CoO film was investigated, revealing a gigantic change in electrical resistance (ON/OFF current ratio: 10(3)) and fast switching speed (ns level). This solution-based self-assembly procedure, in combination with a topotactic conversion from lamellar hydroxides to corresponding oxides, offers a new alternative to high-performance thin film devices based on transition metal oxide.

DOI： 10.1021/cm1021678

Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr, Ti)O-3 thick epitaxial films (vol 97, 11901, 2010) 査読有り

Mitsumasa Nakajima, Takashi Fujisawa, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Minoru Osada

APPLIED PHYSICS LETTERS 97 巻 ( 18 ) 2010年11月

Crystallization of tungstenbronze-type Ba2NaNb5O15 in high-Nb2O5-content glass: An inelastic light scattering study 査読有り

Yoshihiro Takahashi, Nobuhiro Fujie, Minoru Osada, Hirokazu Masai, Rie Ihara, Takumi Fujiwara

JOURNAL OF APPLIED PHYSICS 108 巻 ( 10 ) 2010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 INST PHYSICS

In situ observations of phonon Raman and Boson scattering were performed in high-Nb2O5-content barium-sodium aluminophosphate glass, which crystallizes tungstenbronze-type Ba2NaNb5O15 (BNN), during heating and subsequent cooling processes in order to examine the BNN crystallization dynamics and phase transitions. It is suggested that NbO6 clusters/cohesive regions are present and are subjected to stress by the surrounding aluminophosphate network prior to crystallization of the BNN phase. Furthermore, in the cooling period, a successive phase transition (4/mmm -> 4mm -> mm2) of the BNN phase was observed in the glass-ceramics, implying the possibility of producing functional glass-ceramics with ferroelastic properties. (C) 2010 American Institute of Physics. [doi:10.1063/1.3512909]

DOI： 10.1063/1.3512909

In situ Raman spectroscopy for characterization of the domain contributions to electrical and piezoelectric responses in Pb(Zr, Ti)O-3 films 査読有り

Mitsumasa Nakajima, Hiroshi Nakaki, Yoshitaka Ehara, Tomoaki Yamada, Ken Nishida, Takashi Yamamoto, Minoru Osada, Hiroshi Funakubo

APPLIED PHYSICS LETTERS 97 巻 ( 18 ) 2010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 INST PHYSICS

We employed in situ Raman spectroscopy under electric field for (100)/(001)-oriented tetragonal Pb(Ti0.61Zr0.39)O-3 films with (001)-volume fraction (V-C) of 35%. The increase in V-C was revealed above 200 kV/cm, which resulted in the larger remanent polarization. In addition, the application of high enough field also brings a feature, i.e., large reversible change in V-C with/without electric field that can quantitatively explain the enhanced piezoelectric response. These demonstrate the usefulness of in situ Raman observation to probe the domain contributions to the electrical and piezoelectric responses. (C) 2010 American Institute of Physics. [doi:10.1063/1.3502591]

DOI： 10.1063/1.3502591

Formation of spherulite and metastable phase in stoichiometric Ba2Si3O8 glass 査読有り

Yoshihiro Takahashi, Hirokazu Masai, Minoru Osada, Rie Ihara, Takumi Fujiwara

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 巻 ( 1382 ) 頁： 955 - 958 2010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：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

We investigated the crystallization and resulting morphology of a stoichiometric barium-silicate glass Ba2Si3O8 (B2S3) using TEM observation and Raman spectroscopy. Spherical crystal growth (i.e., spherulite) of stoichiometric B2S3 phase was observed in the heat-treated glass samples, and the size of the spherulites drastically increased as the temperature increased during the heat-treatment process. It was also found that an initial precipitating phase in the precursive stage of crystallization is neither the B2S3 phase nor other crystalline phases in the BaO-SiO2 system. It was deduced that a metastable phase precipitates prior to the formation of spherulite and acts as nucleation site for the spherulite. (C) 2010 The Ceramic Society of Japan. All rights reserved

DOI： 10.2109/jcersj2.118.955

Robust High-kappa Response in Molecularly Thin Perovskite Nanosheets 査読有り

Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Hiroshi Funakubo, Kanta Ono, Kazunori Takada, Takayoshi Sasaki

ACS NANO 4 巻 ( 9 ) 頁： 5225 - 5232 2010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 CHEMICAL SOC

Size-induced suppression of permittivity in perovskite thin films is a fundamental problem that has remained unresolved for decades. This size-effect issue becomes increasingly important due to the integration of perovskite nanofilms into high-kappa capacitors, as well as concerns that intrinsic size effects may limit their device performance. Here, we report a new approach to produce robust high-kappa nanodielectrics using perovskite nanosheet (Ca(2)Nb(3)O(10)), a new class of nanomaterials that is derived from layered compounds by exfoliation. By a solution-based bottom-up approach using perovskite nanosheets, we have successfully fabricated multilayer nanofilms directly on SrRuO(3) or Pt substrates without any interfacial dead layers. These nanofilms exhibit high dielectric constant (>200), the largest value seen so far in perovskite films with a thickness down to 10 nm. Furthermore, the superior high-kappa properties are a size-effect-free characteristic with low leakage current density (<10(-7) A cm(-2)). Our work provides a key for understanding the size effect and also represents a step toward a bottom-up paradigm for future high-kappa devices.

DOI： 10.1021/nn101453v

Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr,Ti)O-3 thick epitaxial films 査読有り

Mitsumasa Nakajima, Takashi Fujisawa, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, Minoru Osada

APPLIED PHYSICS LETTERS 97 巻 ( 11 ) 2010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

We investigated the polarized Raman spectra of a strain-free, unipolar-axis oriented tetragonal Pb(Zr,Ti)O-3 thick epitaxial film. We evaluated the single crystal-like selection rules of the A(1)- and E-symmetry components, and found an anomalous behavior in the angular dependence of the A(1)(1TO)-mode intensity similar to that observed in high-T-c superconductor single crystals. Raman tensor analyses of the A(1)(1TO) mode revealed complex phases may exist between two independent Raman-tensor components even in the single 180 degrees domain state. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488015]

DOI： 10.1063/1.3488015

Transmission electron microscopy and in situ Raman studies of glassy sanbornite: An insight into nucleation trend and its relation to structural variation 査読有り

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

JOURNAL OF APPLIED PHYSICS 108 巻 ( 6 ) 2010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

In situ observation of Raman scattering in glassy sanbornite (BaSi(2)O(5)) showing homogeneous nucleation was performed during heating to investigate the structural variation in the glassy/supercooled-liquid phase in the pre- and postnucleation regimes. It was observed that the formation of Q(2) units accelerates around 400 degrees C, which is well below T(g), just after structural relaxation in the Ba-enriched/-cohesive region. The relation between the structural variation and the nucleation trend in glassy sanbornite was also discussed on the basis of transmission electron microscopy and in situ Raman results and previous Boson observation [Takahashi et al. Appl. Phys. Lett. 94, 211907 (2009). (C) 2010 American Institute of Physics. [doi:10.1063/1.3487473]

DOI： 10.1063/1.3487473

Inelastic light scattering from nanocrystallizing niobiotellurite glass: an insight into the metastable phase and phase-transformation dynamics 査読有り

Yoshihiro Takahashi, Naoki Iwafuchi, Minoru Osada, Hirokazu Masai, Rie Ihara, Takumi Fujiwara

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 巻 ( 1381 ) 頁： 814 - 818 2010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

In situ observations of inelastic light scattering of Raman and Boson regions were performed in nanocrystallized 15K(2)O-15Nb(2)O(5)-70TeO(2) glass to investigate nanocrystallization dynamics during the heating process. These in situ observations revealed a drastic structural rearrangement during the evolution of metastable K[Nb1/3Te2/3](2)O-4.8 nanocrystals. It is suggested that the distortion of the octahedral NbO6 unit being released in the glassy phase is the key to nanocrystallization. (C) 2010 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.118.814

Lithium silicon sulfide as an anode material in all-solid-state lithium batteries 査読有り

Bui Thi Hang, Tsuyoshi Ohnishi, Minoru Osada, Xiaoxiong Xu, Kazunori Takada, Takayoshi Sasaki

JOURNAL OF POWER SOURCES 195 巻 ( 10 ) 頁： 3323 - 3327 2010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

The electrochemical properties of Li(2)SiS(3) were investigated in a solid electrolyte. Li(2)SiS(3) was converted to elemental Si, and the resultant Si was formed into Si-Li alloy in the reduction process; however, the reverse reaction was not completed due to the loss of electronic conduction upon reoxidation. Fes was dispersed as a conductive additive in Li(2)SiS(3) films by pulsed laser deposition (PLD). The addition allowed successive reactions to proceed at a large capacity with small capacity-fading during the cycling process in spite of the small FeS fraction. This result indicates that Li(2)SiS(3) + Fes thin film is a promising anode for solid-state lithium batteries. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2009.11.136

Impact of perovskite layer stacking on dielectric responses in KCa2Nan-3NbnO3n+1 (n=3-6) Dion-Jacobson homologous series 査読有り

Bao-Wen Li, Minoru Osada, Yasuo Ebina, Tadashi C. Ozawa, Renzhi Ma, Takayoshi Sasaki

APPLIED PHYSICS LETTERS 96 巻 ( 18 ) 2010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：AMER INST PHYSICS

The dielectric properties of KCa(2)Na(n-3)NbnO(3n+1) (n=3-6) Dion-Jacobson homologous series have been investigated. The dielectric constants (epsilon) increase with the number of octahedral units (n), and the n=6 compound (KCa2Na3Nb6O19) exhibits a stable dielectric response with epsilon = similar to 500 between 1 kHz and 1 MHz. This n-dependent behavior is similar to those observed in other layered perovskites such as Ruddlesden-Popper and Aurivillius phases. Raman scattering studies reveal that increase in n in KCa2Nan-3NbnO3n+1 leads to higher polarizability of the lattice and softening of the lowest-frequency phonon mode, which is responsible for the observed enhancement in epsilon with n. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3402761]

DOI： 10.1063/1.3402761

酸化物ナノシートの誘電材料および磁気材料への応用

長田実, 佐々木高義

表面技術 = The journal of the Surface Finishing Society of Japan 61 巻 ( 1 ) 頁： 18 - 22 2010年1月

Engineered interfaces of artificial perovskite oxide superlattices via nanosheet deposition process 査読有り

B. W. Li, M. Osada, T. C. Ozawa, Y. Ebina, K. Akatsuka, R. Ma, H. Funakubo, T. Sasaki

ACS Nano 4 巻頁： 6673-6680 2010年

Robust high-k response in molecularly thin perovskite nanosheets 査読有り

M. Osada, Y. Ebina, H. Funakubo, K. Ono, K. Takada, T. Sasaki

ACS Nano 4 巻頁： 5225-5232 2010年

A-Site-Modified Perovskite Nanosheets and Their Integration into High-kappa Dielectric Thin Films with a Clean Interface 査読有り

Bao-Wen Li, Minoru Osada, Tadashi C. Ozawa, Kosho Akatsuka, Yasuo Ebina, Renzi Ma, Kanta Ono, Hiroshi Funakubo, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS 49 巻 ( 9 ) 2010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：JAPAN SOC APPLIED PHYSICS

We investigated dielectric properties of La1-xEuxNb2O7 perovskite nanosheets in order to study the effect of A-site modification on dielectric properties. Langmuir-Blodgett deposition was employed to fabricate multilayer nanofilms of perovskite nanosheets. In these nanosheets, A-site modification with Eu3+ ions improves the leakage current characteristics and, at the same time, reduces permittivity. The slight modification with Eu3+ ions in La0.95Nb2O7 nanosheets causes a 50% reduction in epsilon(r) value. We also discuss the high-kappa properties of La0.95Nb2O7 nanosheets by performing detailed investigations based on first-principles calculations and interfacial structures. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.09MA01

Well-Controlled Crystal Growth of Zinc Oxide Films on Plastics at Room Temperature Using 2D Nanosheet Seed Layer 査読有り

Tatsuo Shibata, Tsuyoshi Ohnishi, Isao Sakaguchi, Minoru Osada, Kazunori Takada, Toshihiro Kogure, Takayoshi Sasaki

JOURNAL OF PHYSICAL CHEMISTRY C 113 巻 ( 44 ) 頁： 19096 - 19101 2009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

ZnO crystal films having a nearly perfect (001) orientation were successfully grown at room temperature on plastic and glass substrates by modifying their surface with Cs(4)W(11)O(36) nanosheets through a solution-based process. To clarify the effect of the monolayer film of Cs(4)W(11)O(36) nanosheets, the films were characterized by X-ray diffraction (XRD), 2D X-ray diffraction (2D-XRD), and high-resolution transmission electron microscopy (HRTEM). The results showed that the introduction of a typical 2D crystal surface with 2D-hexagonal structure (a = 0.727 nm) of Cs(4)W(11)O(36) nanosheet promotes high-quality crystal growth of (001) oriented ZnO film (a = 0 325 nm). Highly crystalline texture directly formed on top of the substrates has been, to the best of our knowledge, realized for the first time, and it dramatically improves the film property, especially at the small film thickness region of <50 nm. The resistivity of the ZnO films significantly decreased when the films were fabricated on glass or plastic substrates with the nanosheet seed layer

DOI： 10.1021/jp9074288

Orientation controlled deposition of Pb(Zr,Ti)O-3 films using a micron-size patterned SrRuO3 buffer layer 査読有り

Ken Nishida, Takashi Yamamoto, Minoru Osada, Osami Sakata, Shigeru Kimura, Keisuke Saito, Masamichi Nishide, Takashi Katoda, Shintaro Yokoyama, Hiroshi Funakubo

JOURNAL OF MATERIALS SCIENCE 44 巻 ( 19 ) 頁： 5339 - 5344 2009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：SPRINGER

Orientation controlled, micron-sized dot-patterned PZT films were grown by metal organic chemical vapor phase deposition (MOCVD), and their crystal structure was evaluated. A micron-size dot-patterned SrRuO3 (SRO) buffer layer was initially prepared by MOCVD through a metal mask on the (111) Pt/Ti/SiO2/Si substrate. Then, a PZT film was deposited over the entire substrate. Micron-beam X-ray diffraction and Raman spectroscopy indicated that (111)-orientated PZT was prepared on the SRO covered area, while the (100)/(001)-orientated one was directly grown on Pt-covered substrates. The PZT film grown on SRO was thinner than that on the Pt-covered substrate. The estimated ferroelectric property on the center of the dot pattern was larger than that at the circumference by Raman spectroscopy because the strain is accelerated at the center of the dot.

DOI： 10.1007/s10853-009-3683-5

Synthesis of Mn-Substituted Titania Nanosheets and Ferromagnetic Thin Films with Controlled Doping 査読有り

Xiaoping Dong, Minoru Osada, Hidekazu Ueda, Yasuo Ebina, Yoshinori Kotani, Kanta Ono, Shigenori Ueda, Keisuke Kobayashi, Kazunori Takada, Takayoshi Sasaki

CHEMISTRY OF MATERIALS 21 巻 ( 19 ) 頁： 4366 - 4373 2009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：AMER CHEMICAL SOC

We report the synthesis of Mn-substituted titania nanosheets and the preparation of room-temperature ferromagnetic thin films via layer-by-layer assembly of these nanosheets. Ti(5.2-2x)/6Mnx/2O2 (x = 0.0-0.4) nanosheets were synthesized by delaminating layered titanates [K0.8Ti(5.2-2x)/3Li(0.8-x)/3-MnxO(4)], in which the Mn content was systematically controlled by Li+ doping. We found that Mn content in the host layers was preserved upon exfoliation, and controlled Mn doping was achieved in exfoliated Ti(5.2-2x)/6Mnx/2O2 (x = 0.0-0.4) nanosheets, where Li+ tons were completely extracted by acid-exchange reaction in the exfoliation process. The multilayer films of Ti(5.2-2x)/6Mnx/2O2 (x = 0.0-0.4) nanosheets exhibit a clear magnetic hysteresis loop at room-temperature in similar to what observed in ferromagnetic Ti1-xCoxO2 nanosheets. Electronic absorption, magnetic circular dichroism, and hard X-ray photoelectron spectroscopy were used to identify Mn-derived states, and analyze the properties of these states related to ferromagnetism. The first-principles calculation of Ti(5.2-2x)/6Mnx/2O2 was also employed to characterize the doping effect on electronic structures.

DOI： 10.1021/cm900210m

Solution-Based Fabrication of Perovskite Nanosheet Films and Their Dielectric Properties 査読有り

Bao-Wen Li, Minoru Osada, Tadashi C. Ozawa, Renzhi Ma, Kosho Akatsuka, Yasuo Ebina, Hiroshi Funakubo, Shigenori Ueda, Keisuke Kobayashi, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS 48 巻 ( 9 ) 2009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：JAPAN SOCIETY APPLIED PHYSICS

We report a solution-based approach for fabricating perovskite nanofilms using a La(0.95)Nb(2)O(7) perovskite nanosheet, a two-dimensional nanomaterial prepared by delaminating layered perovskite KLa(0.95)Nb(2)O(7) into single-molecule-thick sheets. A layer-by-layer approach using Langmuir-Blodgett deposition was effective for fabricating uniform and highly dense nanofilms of perovskite nanosheets on an atomically flat SrRuO(3) substrate. Structural analysis using X-ray diffraction, transmission electron microscopy, and hard X-ray photoelectron spectroscopy revealed that these films are composed of a well-ordered lamellar structure without an interfacial dead layer. The nanofilms showed stable dielectric response with epsilon(r) similar or equal to 45 for thickness even down to 6 nm. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.09KA15

Raman Spectroscopy Evaluation of Oxygen Vacancy Migration by Electrical Field in Multilayer Ceramic Capacitors 査読有り

Ken Nishida, Hiroshi Kishi, Minoru Osada, Hiroshi Funakubo, Masamichi Nishide, Hironari Takeuchi, Takashi Katoda, Takashi Yamamoto

JAPANESE JOURNAL OF APPLIED PHYSICS 48 巻 ( 9 ) 2009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：JAPAN SOCIETY APPLIED PHYSICS

Raman spectroscopy is used to evaluate migration behavior of oxygen vacancies in BaTiO(3)-based multilayer ceramic capacitors with Ni internal electrodes (Ni-MLCCs) before and after a highly accelerated life test (HALT). The B(1) phonon mode of BaTiO(3) that is associated with oxygen vibration was hardened and broadened near the Ni electrodes before HALT. However, the hardening and broadening of the B, mode were observed near the cathodes after HALT. It is considered that the oxygen vacancies were localized near the Ni electrodes before HALT and they electromigrated toward the cathode because they have the positive charges. These results show that oxygen vacancies migrated and accumulated near the cathode under a dc bias and caused insulation resistance degradation in MLCCs. In addition, Raman spectroscopy is a powerful tool for investigation of structural defect distribution including oxygen vacancies with a relatively high spatial resolution. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.09KF11

Precursive stage of nanocrystallization in niobium oxide-containing glass 査読有り

Yoshihiro Takahashi, Hirokazu Masai, Minoru Osada, Takumi Fujiwara

APPLIED PHYSICS LETTERS 95 巻 ( 7 ) 2009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

In situ observation of inelastic light scattering in Raman and Boson regions was performed in a niobiogermanate glass with a high nucleation ability during heating in order to examine its nanocrystallization dynamics. The relation of structural heterogeneity to the precursive stage of crystallization is also discussed. It is suggested that evolution of nuclei occurs in a nanometric niobate-rich region due to density fluctuation in the supercooled liquid phase prior to nanocrystallization.

DOI： 10.1063/1.3211989

Softer region at boundary of supercooled liquid-crystal in glassy fresnoite 査読有り

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

APPLIED PHYSICS LETTERS 94 巻 ( 24 ) 2009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 INST PHYSICS

The transition between the supercooled liquid (SCL) and crystal phases was investigated by in situ observation of boson peak in a glassy fresnoite (Ba(2)TiSi(2)O(8)) with an extremely high nucleation ability. The glassy fresnoite revealed anomalous boson behavior, in that the boson peak's full width at half maximum diverged at T/T(g)similar to 1.2. This behavior suggests that an elastically softer region exists at the interface of the fresnoite nucleus/crystallite in the SCL state.

DOI： 10.1063/1.3156025

Crystallization and nanometric heterogeneity in glass: In situ observation of the boson peak during crystallization 査読有り

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

PHYSICAL REVIEW B 79 巻 ( 21 ) 2009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 PHYSICAL SOC

In situ measurement of boson peak in several glasses was performed during the crystallization process to elucidate crystallization dynamics. In this study, it was experimentally illustrated that a drastic decrease in elasticity and damping of the boson peak occurred during the crystallization process when T/T(g)similar to 1.1-1.2. A possible mechanism for the crystallization precursive stage is also discussed, which integrates our boson peak observation results, Hikima's description [J. Mol. Struct. 479, 245 (1999)], Cabral's thermodynamic data [J. Non-Cryst. Solids 343, 85 (2004)], and other works.

DOI： 10.1103/PhysRevB.79.214204

Structural heterogeneity and homogeneous nucleation of 1BaO-2SiO(2) glass 査読有り

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

APPLIED PHYSICS LETTERS 94 巻 ( 21 ) 2009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：AMER INST PHYSICS

Structural relaxation was examined by in situ Boson peak observation in 1BaO-2SiO(2) glass with homogeneous nucleation tendency, in order to clarify the structural heterogeneity. The relation between the glass structure in the medium-range scale and nucleation feature is also discussed. From the results, it is predicted that a sheet-like structure with a network modifier in the resulting crystal is an essential condition for homogeneous nucleation.

DOI： 10.1063/1.3142394

Construction of Highly Ordered Lamellar Nanostructures through Langmuir-Blodgett Deposition of Molecularly Thin Titania Nanosheets Tens of Micrometers Wide and Their Excellent Dielectric Properties 査読有り

Kosho Akatsuka, Masa-aki Haga, Yasuo Ebina, Minoru Osada, Katsutoshi Fukuda, Takayoshi Sasaki

ACS NANO 3 巻 ( 5 ) 頁： 1097 - 1106 2009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：AMER CHEMICAL SOC

Exfoliated unilamellar titania nanosheets of Ti0.87O2 with a lateral size of 10-30 mu m were deposited layer-by-layer onto various substrates by Langmuir-Blodgett procedure to produce a highly ordered lamellar nanofilms. The nanosheets dispersed in an aqueous suspension containing quaternary ammonium ions as a supporting electrolyte floated spontaneously at the air/liquid interface, and they were successfully transferred onto the substrate after surface compression. Neat tiling of the nanosheets could be realized at an optimized surface pressure. The film thus obtained was exposed to UV light to turn the substrate surface hydrophilic, which was helpful for stable repetition of monolayer deposition. Layer-by-layer growth was confirmed by UV-visible absorption spectra, which showed progressive enhancement of an absorption band due to the nanosheet. Cross-sectional transmission electron microscopy images visualized the ultrathin film homogeneously deposited on the substrate surface and a lamellar fringe of the layer-by-layer assembled nanosheets was clearly resolved at a higher magnification. X-ray diffraction data on the films showed sharp basal reflections up to the seventh order, and Williamson-Hall analysis of the pattern indicated that the film was coherent across the total thickness with respect to X-ray and that the lattice strain was extremely small. In addition, the first basal reflection was accompanied by small satellite peaks, which are accounted for by the Laue interference function. All these features clearly indicate the formation of a highly ordered lamellar nanostructure of the titania nanosheets comparable to artificial lattice films produced via modern vapor-phase deposition processes. The obtained films showed superior dielectric and insulating properties as a reflection of the highly organized film nanoarchitecture.

DOI： 10.1021/nn900104u

Fabrication of novel composites of ZnO-nanoparticles and magadiite 査読有り

Kiyoshi Ozawa, Yasuhiro Nakao, Zhenxiang Cheng, Defa Wang, Minoru Osada, Reika Okada, Kazuhiko Saeki, Hiroyasu Itoh, Fumio Iso

MATERIALS LETTERS 63 巻 ( 3-4 ) 頁： 366 - 369 2009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

Novel composites of ZnO-nanoparticles and magadiite were Successfully prepared by a simple ion-exchange technique in an aqueous suspension of magadiite (Na(2)Si(14)O(29)center dot nH(2)O) and Zn(NO(3))(2). The TEM and STEM measurements showed that the composites have a structure in which ZnO-nanoparticles with relatively uniform particle sizes are well dispersed within the interlaminar spaces of the magadiite matrix. The particle sizes of the ZnO-nanoparticles were found to depend oil the heat-treatment temperature: the average particle sizes are similar to 2.6, similar to 2.8, similar to 4.4 and similar to 4.6 nm, respectively, for the temperatures of 40, 180, 300 and 600 degrees C. It Was also found that the ZnO nanoparticles crystallize and form a single-crystalline particle when the temperature exceeds similar to 300 degrees C. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2008.10.038

Exfoliated oxide nanosheets: new solution to nanoelectronics 招待有り査読有り

M. Osada, T. Sasaki

J. Mater. Chem. 19 巻頁： 2503-2511 2009年

Anomalous Boson Behavior and Nanometric Heterogeneity in Glassy Fresnoite 査読有り

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

APPLIED PHYSICS EXPRESS 1 巻 ( 12 ) 2008年12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：JAPAN SOCIETY APPLIED PHYSICS

In-situ observation of the boson peak, omega(BP), Of as-quenched and annealed glassy Ba(2)TiGe(2)O(8) (BTG) and Ba(2)TiSi(2)O(8) (BTS) was performed during a heating process. Although annealed glassy BTG and BTS indicated a monotonous decrease in omega(BP) with temperature, the asquenched varieties, which included internal stress, revealed anomalous boson behavior at similar to 600 degrees C, lower than each one's glass-transition temperature. It was suggested that the omega(BP) anomaly was caused by beta-relaxation. This experimental result also supports the inhomogeneous structure (or cluster) model of glass. (C) 2008 The Japan Society of Applied Physics

DOI： 10.1143/APEX.1.121901

Raman spectroscopy study of oxygen vacancies in PbTiO3 thin films generated heat-treated in hydrogen atmosphere 査読有り

Ken Nishida, Minoru Osada, Hironari Takeuchi, Ishimoto Yosiaki, Joe Sakai, Nobuaki Ito, Rikyu Ikariyama, Takafumi Kamo, Takashi Fujisawa, Hiroshi Funakubo, Takashi Katoda, Takashi Yamamoto

JAPANESE JOURNAL OF APPLIED PHYSICS 47 巻 ( 9 ) 頁： 7510 - 7513 2008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：JAPAN SOC APPLIED PHYSICS

Raman spectroscopy is utilized to study the evaluation of vacancies in PbTiO3 thin films subjected to hydrogen atmosphere heat treatment. The B-1 mode consisted of only oxygen ion vibration was shifted to lower frequency with increasing heat treatment temperature. It was considered that the oxygen ions were lacking from PbTiO3, and that oxygen vacancies were generated. It was found that the frequency of the B-1 mode is proportional to oxygen ion content. Pb ions were also lacking in the PbTiO3 thin films with oxygen ions number of oxygen vacancies was larger than that of Pb ions. We suggest that the Raman spectroscopy is a suitable tool for the evaluation of oxygen vacancies in PbTiO3 thin films.

DOI： 10.1143/JJAP.47.7510

Interfacial modification for high-power solid-state lithium batteries 査読有り

Kazunon Takada, Narumi Ohta, Lianqi Zhang, Katsutoshi Fukuda, Isao Sakaguchi, Renzhi Ma, Minoru Osada, Takayoshi Sasaki

SOLID STATE IONICS 179 巻 ( 27-32 ) 頁： 1333 - 1337 2008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

Interfaces between LiCoO2 and sulfide solid electrolytes were modified in order to enhance the high-rate capability of solid-state lithium batteries. Thin films of oxide solid electrolytes, Li4Ti5O12, LiNbO3, and LiTaO3, were interposed at the interfaces as buffer layers. Changes in the high-rate performance upon heat treatment revealed that the buffer layer should be formed at low temperature to avoid thermal diffusion of the elements. Buffer layers of LiNbO3 and LiTaO3 can be formed at low temperature for the interfacial modification, because they show high ionic conduction in their amorphous states, and so are more effective than Li4Ti5O12 for high-power densities. (c) 2008 Elsevier BY All rights reserved.

DOI： 10.1016/j.ssi.2008.02.017

X-ray nanospectroscopic characterization of a molecularly thin ferromagnetic Ti(1-x)Co(x)O(2) nanosheet 査読有り

Yoshinori Kotani, Toshiyuki Taniuchi, Minoru Osada, Takayoshi Sasaki, Masato Kotsugi, F. Z. Guo, Yoshio Watanabe, Masato Kubota, Kanta Ono

APPLIED PHYSICS LETTERS 93 巻 ( 9 ) 2008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

We investigated the local electronic structures of a molecularly thin ferromagnetic Ti(0.8)Co(0.2)O(2) nanosheet by means of x-ray nanospectroscopy with spectroscopic photoemission and low energy electron microscopy. By analyzing the Co 2p x-ray absorption and photoemission spectra, the chemical state of doped Co ions in individual Ti(0.8)Co(0.2)O(2) nanosheet was found to be Co(2+) low-spin state, which is consistent with previous magnetization data and first-principles calculation [M. Osada , Phys. Rev. B 73, 153301 (2006)]. Furthermore, we employed photoelectron emission microscopy to image the variation in chemical states in Ti(0.8)Co(0.2)O(2) nanosheets with different stacking structures and clarified the identical Co(2+) low-spin state in monolayer and overlapped cases. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2976550

Langmuir-Blodgett fabrication of nanosheet-based dielectric films without an interfacial dead layer 査読有り

Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Yoshinori Kotani, Kanta Ono, Hiroshi Funakubo, Shigenori Ueda, Keisuke Kobayashi, Kazunori Takada, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS 47 巻 ( 9 ) 頁： 7556 - 7560 2008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：JAPAN SOC APPLIED PHYSICS

Langmuir-Blodgett (LB) deposition was employed to fabricate high-kappa dielectric nanofilms of titania nanosheets. The LB-based layer-by-layer approach using an atomically flat SrRuO(3) substrate is effective for the fabrication of atomically uniform and highly dense nanofilms. These films exhibited both high dielectric constant (kappa similar to 123) and low leakage current density (J < 10(-7) A cm(-2)) for thicknesses down to 5 nm, while eliminating the size-effect problems encountered in current high-kappa From analyses of interfacial structures by transmission electron microscopy and hard X-ray photoelectron spectroscopy. we have clarified that the films are composed of a well-ordered lamellar structure without an interfacial dead layer. According to first-principles calculations, a highly polarizable nature of titania nanosheets can bring improved dielectric properties. yielding high-kappa values even in an ultrathin geometry.

DOI： 10.1143/JJAP.47.7556

Gigantic magneto-optical effects induced by (Fe/Co)-cosubstitution in titania nanosheets 査読有り

Minoru Osada, Masayuki Itose, Yasuo Ebina, Kanta Ono, Shigenori Ueda, Keisuke Kobayashi, Takayoshi Sasaki

APPLIED PHYSICS LETTERS 92 巻 ( 25 ) 2008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 INST PHYSICS

Magneto-optical Faraday effect has been investigated for 3d-transition-metal-substituted titania nanosheets Ti(1-x)M(x)O(2) (M=Fe,Co). In Ti(0.8)Co(0.2)O(2) and Ti(0.6)Fe(0.4)O(2) nanosheets, a strong magneto-optical response (similar to 10(4) deg/cm) appeared near the absorption edge at 260 nm. We find that tailoring magneto-optical properties could be achieved by (Fe/Co) cosubstitution and an optimally doped Ti(0.75)Fe(0.1)Co(0.15)O(2) nanosheet exhibits a gigantic magneto-optical response (similar to 10(5) deg/cm) over the wide wavelength region (400-750 nm). By analyzing electronic structures from first-principle calculations, we have clarified that the d-d transitions are responsible for the gigantic signal in (Fe/Co)-cosubstituted nanosheets. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2937094

Synthesis and electrochemistry of new layered (1-x) LiVO2 center dot xLi(2)TiO(3) (0 <= x <= 0.6) electrode materials 査読有り

Lianqi Zhang, Kazunori Takada, Narumi Ohta, Minoru Osada, Takayoshi Sasaki

JOURNAL OF POWER SOURCES 174 巻 ( 2 ) 頁： 1007 - 1011 2007年12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

Novel electrode materials with nominal compositions of (1 - x)LiVO2 center dot xLi(2)TiO(3) (0 <= x <= 0.6) were synthesized by carbothermal reduction reaction. All the materials were identified to have a layered structure and can be considered as a solid solution related to LiVO2-Li2TiO3 system, in which Li layers was alternately stacked with the layers made of mixture of Li, V, and Ti in a ccp array of oxygen. The redox reaction associated with vanadium ions was not reversible in LiVO2; however, introduction of the redox couple into Li2TiO3 made it much more reversible. A reversible capacity of about 120 mAh g(-1) remained after 90 cycles for the samples with x = 0.5 and 0.6, when they were cycled in the voltage range of 1.0-4.8 V. (c) 2007 Elsevier B.V All rights reserved.

DOI： 10.1016/j.jpowsour.2007.06.082

Hydration of sodium cobalt oxide 査読有り

Hiroya Sakurai, Minoru Osada, Eiji Takayama-Muromachi

CHEMISTRY OF MATERIALS 19 巻 ( 25 ) 頁： 6073 - 6076 2007年12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

It was found that Na+ ions in NaxCoO2 can be partially substituted by H3O+ ions while maintaining a constant Co valence simply by immersion in water. The Magnetic Susceptibility of Na-x(H3O)(z)CoO2 (X + z = 0.70) changed drastically from Curie-Weiss type to Pauli paramagnetic type, indicating that the electronic band structure was modified by the isovalent ion substitution of Na+/H3O+. Two possible origins of the change in the electronic structure are discussed.

DOI： 10.1021/cm0714786

Solution-based fabrication of high-kappa dielectric nanofilms using titania nanosheets as a building block 査読有り

Minoru Osada, Kosho Akatsuka, Yasuo Ebina, Hiroshi Funakubo, Takanori Kiguchi, Kazunori Takada, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 巻 ( 10B ) 頁： 6979 - 6983 2007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：INST PURE APPLIED PHYSICS

We have demonstrated a novel procedure for fabricating high-kappa dielectric nanofilms by using a titania nanosheet as a building block. The layer-by-layer assembly of titania nanosheets using an atomically flat SrRuO3 substrate is advantageous as a means of fabricating atomically uniform multilayer high-kappa nanofilms. High-resolution transmission electron microscopy revealed that these multilayer nanofilms are composed of a well-ordered lamellar structure without an interfacial dead layer. These nanofilms exhibited both high dielectric constant (epsilon(r)similar to 125) and low leakage current density (J < 10(-7) A/cm(2)) even for thicknesses as low as 10nm. These results indicate that the titania nanosheet is a very promising candidate as a high-kappa nanoblock, and its bottom-up fabrication provides new opportunities for the development of high-kappa devices.

DOI： 10.1143/JJAP.46.6979

LiNbO3-coated LiCoO2 as cathode material for all solid-state lithium secondary batteries 査読有り

Narumi Ohta, Kazunori Takada, Isao Sakaguchi, Lianqi Zhang, Renzhi Ma, Katsutoshi Fukuda, Minoru Osada, Takayoshi Sasaki

ELECTROCHEMISTRY COMMUNICATIONS 9 巻 ( 7 ) 頁： 1486 - 1490 2007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：ELSEVIER SCIENCE INC

The further enhancement of high-rate capabilities for all solid-state lithium secondary batteries is reported. A LiNbO3 layer of nanometer thickness was interposed between LiCoO2 and sulfide solid electrolyte as buffer layer. This greatly reduced the interfacial resistance in the cathode and enhanced the high-rate capabilities of solid-state lithium batteries, providing good prospects for practical application of lithium secondary batteries free from safety issues. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elecom.2007.02.008

AgI/Ag heterojunction nanowires: Facile electrochemical synthesis, photoluminescence, and enhanced ionic conductivity 査読有り

Changhao Liang, Kazuya Terabe, Tohru Tsuruoka, Minoru Osada, Tsuyoshi Hasegawa, Masakazu Aono

ADVANCED FUNCTIONAL MATERIALS 17 巻 ( 9 ) 頁： 1466 - 1472 2007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：WILEY-V C H VERLAG GMBH

The construction of an electronic-conductor/ionic-conductor heterojunction in a well-defined nanostructure is the basis of studying interfacial and bulk transport and the reactions of ions and electrons at the nanoscale level. An ionic-conductor/metal (AgI/Ag) beterostructured nanowire array is easily fabricated by a template-confined, step-electrochemical technique. The structural and morphological evolution of the AgI/Ag heterostructure before and after its release from the anodic aluminum oxide (AAO) membrane is characterized by scanning electron microscopy, X-ray diffraction, and optical spectroscopy. The structural disordering of released AgI is suggested by the appearance of a broad photoluminescence emission band at longer wavelengths and a short-range-order-like Raman peak. The ionic conductivity of the AgI nanowire embedded inside the insulating AAO membrane is measured as being on the order of 10(-3) S cm(-1), which is an enhancement by two to three orders of magnitude compared with that of bulk polycrystalline AgI at room temperature. This electrochemical method could be useful in fabricating other pure and mixed ionic conductors in heterojunction nanostructures.

DOI： 10.1002/adfm.200600590

Probing Intrinsic Polarization Properties in Bismuth-Layered Ferroelectric Films 査読有り

Takayuki WATANABE, Hiroshi FUNAKUBO, Minoru OSADA, Hiroshi UCHIDA, Isao OKADA, Brian J. RODRIGUEZ, Alexei GRUVERMAN

Applied Physics Letters 90 巻 ( 11 ) 頁： 112914 - 112914-3 2007年3月

New misfit-layered cobalt oxide (CaOH)(1.14)CoO2 査読有り

Mitsuyuki Shizuya, Masaaki Isobe, Yuji Baba, Takuro Nagai, Minoru Osada, Kosuke Kosuda, Satoshi Takenouchi, Yoshio Matsui, Eiji Takayama-Muromachi

JOURNAL OF SOLID STATE CHEMISTRY 180 巻 ( 1 ) 頁： 249 - 259 2007年1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：ACADEMIC PRESS INC ELSEVIER SCIENCE

We synthesized a new cobalt oxide (CaOH)(1.14)CoO2 by utilizing a high-pressure technique. X-ray and electron diffraction studies revealed that the compound has a layered structure that consists of Cdl(2)-type CoO2 layers and rock-salt-type double CaOH atomic layers. The two subcells have incommensurate periodicity along the a-axis, resulting in a misfit-layered structure. From resistivity and Seebeck coefficient measurements, we have shown that the two-dimensional (2-D) variable-range hopping (VRH) regime with hole conduction is dominant at low temperature for this compound. As temperature increases, the conduction mechanism undergoes crossover from the 2-D VRH regime to a thermal activation-energy-type regime. (c) 2006 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2006.10.014

Impacts of intrinsic defects on luminescence properties of CuAlS2 査読有り

Yuichiro Kuroki, Tomoichiro Okamoto, Masasuke Takata, Minoru Osada

APPLIED PHYSICS LETTERS 89 巻 ( 22 ) 2006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 INST PHYSICS

The authors report on Raman scattering of CuAlS2 in order to study the influences of intrinsic defects on luminescence properties. The A(1) mode is dominated in stoichiometric samples, whereas sulfur-poor conditions prepared at high temperatures (>= 800 degrees C) cause defect-specific shift and broadening. They also find that additional mode (at 330 cm(-1)) caused by antisite defects is resonated at 2.16 eV excitation, in accordance with visible luminescence attributed to donor-acceptor pair (DAP) emission in photoluminescence. These results suggest that the DAP emissions may be caused by the defect complexes such as Al-Cu-V-Cu and V-S-V-Cu, which reduces ultraviolet excitonic emission in this system. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2400101

Resonant two-phonon Raman scattering as a probe of hole crystal formation in Sr14-xCaxCu24O41 査読有り

Joakim Holmlund, Jakob Andreasson, Christopher S. Knee, Joakim Backstrom, Mikael Kall, Minoru Osada, Takashi Noji, Yoji Koike, Masato Kakihana, Lars Borjesson

PHYSICAL REVIEW B 74 巻 ( 13 ) 2006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：AMERICAN PHYSICAL SOC

The charge dynamics of the spin ladder compound Sr14-xCaxCu24O41 with x=0,6,13.6 has been investigated using wavelength- and temperature-dependent phonon Raman scattering on single crystals. In the unsubstituted, x=0, compound, a set of sharp two-phonon lines shows a strong increase in intensity below T similar to 200 K for light polarized along the ladder layer and with excitation energy close to the charge transfer gap similar to 1.9 eV. The temperature dependence of the strongly enhanced two-phonon bands below 200 K closely follows the recently reported formation of a standing charge density wave in the ladders [P. Abbamonte , Nature 431, 1078 (2004)]. Upon calcium substitution the polarized resonant Raman response rapidly decreases, signaling an increase of hole mobility in the ladder units. Temperature-dependent measurements of the x=13.6 sample indicate mobility of holes down to < 8 K.

DOI： 10.1103/PhysRevB.74.134502

Synthesis and electrochemical propeities of Li2S-B2S3-Li4SiO4 査読有り

Yoshikatsu Seino, Kazunori Takada, Bong-Chull Kim, Lianqi Zhang, Narumi Ohta, Hiroaki Wada, Minoru Osada, Takayoshi Sasaki

SOLID STATE IONICS 177 巻 ( 26-32 ) 頁： 2601 - 2603 2006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：ELSEVIER SCIENCE BV

New Li+ ion-conductive glasses Li2S-B2S3-Li4SiO4 were synthesized by rapid quenching, and they were transformed into glass ceramics by heat treatment. The heat treatment increased the ionic conductivities of the Li4SO4-doped glasses, and the highest ionic conductivity observed in the system was 1.0 x 10(-3) S cm(-1) at room temperature. The glass ceramics were highly stable against electrochemical oxidation with a wide electrochemical window of 10 V. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2006.01.005

Site occupancy analysis on the enhancement in Dy-substituted Pb(Zr,Ti)O-3 film 査読有り

Ken Nishida, Minoru Osada, Hiroshi Uchida, Hiroshi Nakaki, Seiichiro Koda, Hiroshi Funaku, Takashi Katoda

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 巻 ( 9B ) 頁： 7548 - 7551 2006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：INST PURE APPLIED PHYSICS

The effect of site selectivity on the ferroelectric polarization property was investigated in Dy-substituted Pb(Zr0.4Ti0.6)O-3 films prepared on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution method. Dy ions were introduced, assuming Pb or Zr and Ti site substitutions in Pb(Zr0.40Ti0.60)O-3 with x ranging from 0 to 0.06. Site occupation was determined by Raman spectroscopy. Dy ions selectively replaced the assumed sites at a low x value; however, these ions interdiffused to opposite sites at a high x value. Remnant polarization was enhanced when Dy ions selectivity substituted the Zr and Ti sites at a low x value, while it was contrarily degraded by Ph site substitution. These results provide useful guidelines for ferroelectric property improvement by ion substitution in Pb(Zr0.4Ti0.6)O-3.

DOI： 10.1143/JJAP.45.7548

Enhancement of the high-rate capability of solid-state lithium batteries by nanoscale interfacial modification 査読有り

Narumi Ohta, Kazunori Takada, Lianqi Zhang, Renzhi Ma, Minoru Osada, Takayoshi Sasaki

ADVANCED MATERIALS 18 巻 ( 17 ) 頁： 2226 - + 2006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-BLACKWELL

The high-rate capability of solid-state, rechargeable lithium batteries with sulfide electrolytes is significantly improved when the LiCoO(2) particles are spray-coated with a Li(4)Ti(5)O(12) film with a thickness of several nanometers (see figure). The power densities of the solid-state battery with the coated LiCoO(2) are comparable to those of commercialized lithium-ion cells.

DOI： 10.1002/adma.200502604

酸化物ナノシート−ナノシートの積層制御と機能化−

佐々木高義, 海老名保男, 長田実

セラミックス 41 巻 ( 4 ) 頁： 290 - 295 2006年4月

Investigation of domain distribution in patterned PZT thin films using Raman spectroscopy 査読有り

Ken Nishida, Minoru Osada, Shintaro Yokoyama, Kenji Takahashi, Hiroshi Funakubo, Takashi Katoda

Transactions of the Materials Research Society of Japan, Vol 31, No 1 31 巻 ( 1 ) 頁： 27 - 30 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：ELSEVIER SCIENCE BV

Domain distribution, crystallinity and ferroelectric properties of micro-patterned PZT thin films were characterized with polarized Raman spectroscopy. The patterned PZT film grown on the Pt bottom electrode had good crystallinity independent of the pattern size. On the other hand, the PZT film grown outside the Pt bottom electrode had poor crystallinity or almost amorphous. The c-domain volume was estimated to be 55% from the polarized Raman spectra on the Pt bottom electrode. These results demonstrate that Raman spectroscopy is a very useful means to characterize micro-patterned PZT films.

Characterization of superconducting sodium cobalt oxide bilayer-hydrate 査読有り

K Takada, K Fukuda, M Osada, Nakai, I, F Izumi, RA Dilanian, K Kato, M Takata, H Sakurai, E Takayama-Muromachi, T Sasaki

CHINESE JOURNAL OF PHYSICS 43 巻 ( 3 ) 頁： 556 - 565 2005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：PHYSICAL SOC REPUBLIC CHINA

new superconductor of sodium cobalt oxide bilayer-hydrate, Na(X)COo(2)center dot yH(2)O (X approximate to 0.35), was characterized by chemical and structure analyses. The chemical analyses showed that the formal valence of Co was +3.4, which was much lower than +3.65 that had been estimated from the Na content, x. The deviation from the charge neutralization was considered to be compensated by oxonium (H3O+) ions, which were evidenced by Raman spectroscopy. Structural studies based on Raman spectroscopy and synchrotron X-ray powder diffraction suggested that the H3O+ ions occupy the same crystallographic sites as the Na+ ions.

Synthesis and electrochemistry of layered (1-x)LiNi0.5Mn0.5O2 • xLi[Li1/3Mn2/3]O2 • yLiCoO2 (0≦x=y≦0.3 and x+y=0.5) cathode materials 査読有り

Zhang, L, Takada, K, Ohta, N, Osada, M, Fukuda, K, Wang, L, Sasaki, T, Watanabe, M

Journal of Power Sources ( 146 ) 頁： 598 - 601 2005年

Synthesis and Electrical Properties of Sr- and Nb-Cosubstituted Bi4-xSrxTi3-xNbxO12 Polycrystalline Thin Films 査読有り

Hirofumi MATSUDA, Takashi IIJIMA, Hiroshi UCHIDA, Isao OKADA, Takayuki WATANABE, Hiroshi FUNAKUBO, Minoru OSADA, Masato KAKIHANA

Jpn. J. Apply. Phys. 42 巻 ( 8 ) 頁： 949 - 952 2003年8月

ラマン分光法による機能性セラミックスの評価査読有り

長田実, 垣花眞人

機能材料 23 巻 ( 11 ) 頁： 38 - 48 2003年4月

Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8: Indications of pseudogap effects in nonsuperconducting PrBa2Cu4O8 査読有り

J Backstrom, M Rubhausen, M Kall, L Borjesson, AP Litvinchuk, M Kakihana, M Osada, B Dabrowski

PHYSICAL REVIEW B 61 巻 ( 10 ) 頁： 7049 - 7054 2000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：AMER PHYSICAL SOC

By analysis of the Raman spectra of superconducting YBa2Cu4O8 (Y-124), we observe a suppression of low-energy electronic density of states that we link to changes in the Linewidth of the Ba-phonon mode. These effects occur at a temperature below 150 K, where also anomalies in resistivity and other physical properties take place. We argue that these changes in the Raman spectra of Y-124 are connected to the opening of a pseudogap. Analogous anomalies in resistivity and the Ba-phonon width in the nonsuperconducting homologue PrBa2Cu4O8 (Pr-124) below 150 K suggest that similar pseudogap effects can occur without a following transition to a superconducting state at st lower temperature.

CuO-chain Raman scattering and photoinduced metastability in YBa2Cu3Ox 査読有り

M Kall, M Osada, M Kakihana, L Borjesson, T Frello, J Madsen, NH Andersen, R Liang, P Dosanjh, WN Hardy

PHYSICAL REVIEW B 57 巻 ( 22 ) 頁： 14072 - 14075 1998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 PHYSICAL SOC

Raman measurements in YBa2Cu3Ox (x=6.72-6.82) high-T-c superconductors reveal intense phonon scattering due to an electronic resonance localized near oxygen vacancies on the CuO chains. Below room temperature the resonance can be photobleached in a manner similar to reported persistent photoinduced superconductivity effects, indicating photon-assisted oxygen ordering or electron vacancy capture. By comparing Raman and x-ray diffraction data we establish a correlation between the stability of the photoinduced state and the oxygen-ordering kinetics in the CuO chains.

Raman-active phonons in Bi2Sr2-xLaxCuO6+d: Phonon assignment and charge-redistribution effects 査読有り

M Osada, M Kakihana, M Kall, L Borjesson, A Inoue, M Yashima

PHYSICAL REVIEW B 56 巻 ( 5 ) 頁： 2847 - 2851 1997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：AMERICAN PHYSICAL SOC

Phonon Raman spectra of Bi2Sr2-xLaxCuO6+d single crystals with x values close to 0, 0.4, and 0.8 have been investigated. Room-temperature measurements were performed in the five main polarization geometries, including the c-axis polarized configuration. We identify the 4A(1g) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell, as well as several disorder activated phonon bands from the BiO and/or SrO layers. For an increasing degree of La doping, the O(2)(Sr) A(1g) mode at 624 cm(-1) softens by 12 cm(-1) between x = 0 and x = 0.8. We attribute this softening to a weakening of the Cu-O(2)(Sr)-Bi bond due to a reduction in Cu and Bi valences when going from the overdoped (x = 0) to the underdoped (x = 0.8) regime.

Raman-active phonons in Bi2Sr2Ca1-xYxCu2O8+d (x=0-1): Effects of hole filling and internal pressure induced by Y doping for Ca, and implications for phonon assignments 査読有り

M Kakihana, M Osada, M Kall, L Borjesson, H Mazaki, H Yasuoka, M Yashima, M Yoshimura

PHYSICAL REVIEW B 53 巻 ( 17 ) 頁： 11796 - 11806 1996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：AMERICAN PHYSICAL SOC

The phonon Raman spectra of Bi2Sr2Ca1-xYxCu2O8+d (x=0-1) have been investigated in a number of well-defined single-crystal and polycrystalline samples. From the polarization and Y-doping dependence, and from a comparison with previous reports on Bi-based cuprates, we identify the (6A(1g)+1B(1g)) symmetry modes that are Raman allowed within the ideal body-centered-tetragonal unit cell. A large number of extra ''disorder-induced'' phonon bands are observed in the ab-plane polarized spectra. In contrast to most previous reports, we argue that the c-axis polarized phonon band around 629 cm(-1) is due to the O(2)(Sr)A(1g) vibration, while the exclusively ab-plane polarized band around 463 cm(-1) is induced by the O(3)(Bi)A(1g) vibration. With increasing Y doping we find that the vibrational modes involving atoms in the CuO2 planes rapidly increase in intensity as a result of the reduced metallic screening in the hole-depleted Y-doped samples. We also find that Y substitution gives rise to a substantial hardening of the O(1)(Cu)A(1g) and B-1g phonons by similar to 40 cm(-1), whereas the O(2)(Sr)A(1g) phonon is found to soften by similar to 20 cm(-1), when x increases from 0 to 1. The phonon frequency changes can be explained by the ''internal pressure'' induced by the decrease in the average Ca/Y ion size and an additional ''charge-transfer'' induced by the change in the Cu and Bi valences with Y doping.

Phonon Raman scattering in Y1-xPrxBa2Cu4O8 (x=0-1) and (Y1-xPrx)(2)Ba4Cu7O15-delta (x=0-0.6) 査読有り

M Kall, AP Litvinchuk, P Berastegui, LG Johansson, L Borjesson, M Kakihana, M Osada

PHYSICAL REVIEW B 53 巻 ( 6 ) 頁： 3590 - 3597 1996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：AMERICAN PHYSICAL SOC

We report on a Raman-scattering investigation of phonons in ceramic Y1-xPrxBa2Cu4O8 (Y(1-x)Pr(x)124) with x=0-1, and (Y1-xPrx)(2)Ba4Cu7O15-delta (Y(1-x)Pr(x)247) with x=0-0.6. It is found that the A(g) symmetry phonons of the BaO layers and the CuO double-chain layers increase in frequency with Pr content x, while B-2g and B-3g symmetry phonons decrease in frequency. In the Y(1-x)Pr(x)247 samples we are able to identify two symmetry allowed apical oxygen A(g) modes. The B-1g-like plane oxygen phonon softens by similar to 12% from x=0 to x=1, and exhibits a two-mode behavior at intermediate x in both Y(1-x)Pr(x)124 and Y(1-x)Pr(x)247. Polarized micro-Raman spectra of Pr124 crystallites show that several phonons are asymmetric, exhibiting Fano line shapes similar to what has been found in superconducting Y124. The variation in phonon frequencies with Pr content is similar to what has been reported for the single-chain cuprate Y1-xPrxBa2Cu3O7-delta (Y(1-x)Pr(x)123), and the changes can be understood from the variation in structural parameters. We do not observe any peculiarities that can explain the disappearance of superconductivity, or the different rates of T-c suppression in the three different Y-Ba-Cu-O systems, upon Pr substitution.

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