Faculty Profiles - OSADA Minoru

Papers - OSADA Minoru

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RbBiNb2O7: A New Lead-Free High-T-c Ferroelectric Reviewed

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

CHEMISTRY OF MATERIALS Vol. 24 ( 16 ) page： 3111 - 3113 2012.8

NANOCRYSTALLIZATION AND OPTICAL PROPERTY OF WILLEMITE-TYPE SEMICONDUCTIVE Zn2GeO4 IN GLASS Reviewed

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

FUNCTIONAL MATERIALS LETTERS Vol. 5 ( 2 ) 2012.6

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Effect of annealing at maximum nucleation temperature on boson peak in lithium-disilicate glass Reviewed

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 120 ( 1402 ) page： 256 - 258 2012.6

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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Photochromogenic Nanosheet Crystallites of Tungstate with a 2D Bronze Structure Reviewed

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

INORGANIC CHEMISTRY Vol. 51 ( 3 ) page： 1540 - 1543 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Soft-phonon mode observation in Li2Ge4O9 phase above room temperature Reviewed

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

APPLIED PHYSICS LETTERS Vol. 100 ( 9 ) 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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Two-Dimensional Dielectric Nanosheets: Novel Nanoelectronics From Nanocrystal Building Blocks Reviewed

Minoru Osada, Takayoshi Sasaki

ADVANCED MATERIALS Vol. 24 ( 2 ) page： 210 - 228 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

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

Minoru Osada, Takayoshi Sasaki

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY Vol. 9 ( 1 ) page： 29 - 36 2012.1

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Two-dimensional dielectric nanosheets: novel nanoelectronics from building blocks Invited Reviewed

M. Osada, T. Sasaki

Adv. Mater. Vol. 24 page： 210-228 2012

Solution-Based Fabrication of Perovskite Multilayers and Superlattices Using Nanosheet Process Reviewed

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 9 ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Controlled Polarizability of One-Nanometer-Thick Oxide Nanosheets for Tailored, High-kappa Nanodielectrics Reviewed

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

ADVANCED FUNCTIONAL MATERIALS Vol. 21 ( 18 ) page： 3482 - 3487 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

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

Yoshihiro Takahashi, Minoru Osada, Rie Ihara, Takumi Fujiwara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 80 ( 9 ) 2011.9

Nanoscale Characterization of Domain Structures in Bi4Ti3O12 Single Crystals Using Near-Field Raman Spectroscopy Reviewed

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 9 ) 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Nano-patterning of a TiO2-organic hybrid material using interference of surface plasmon on aluminum Reviewed

Hiroyo Segawa, Satoru Inoue, Minoru Osada, Yoshihiko Takeda

JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY Vol. 221 ( 2-3 ) page： 232 - 238 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：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

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Low-frequency inelastic light scattering of zincogermanate glass in supercooledliquid regime Reviewed

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

JOURNAL OF APPLIED PHYSICS Vol. 109 ( 12 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

In situ Observation of Supercooled Liquid-Crystal Phase Transition in Glassy Ferroelectric LaBGeO5 Reviewed

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 6 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

Orbital reconstruction and interface ferromagnetism in self-assembled nanosheet superlattices Reviewed

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

ACS Nano Vol. 5 page： 6871-6879 2011

Tantalum oxide nanomesh as self-standing one nanometre thick electrolyte Reviewed

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

Energy. Environ. Sci. Vol. 4 page： 3509-3512 2011

Controlled polarizability of one-nanometer-thick oxide nanosheets for tailored, high-k nanodielectrics Reviewed

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

Adv. Funct. Mater. Vol. 21 page： 3482-3487 2011

Crystallization and Morphology of Glassy Sanbornite Reviewed

Yoshihiro Takahashi, Rie Ihara, Takumi Fujiwara, Minoru Osada

ELECTROCERAMICS IN JAPAN XIV Vol. 485 page： 301 - + 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：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

Web of Science

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

Renzhi Ma, Minoru Osada, Linfeng Hu, Takayoshi Sasaki

CHEMISTRY OF MATERIALS Vol. 22 ( 23 ) page： 6341 - 6346 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

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Papers - OSADA Minoru