Faculty Profiles - OSADA Minoru

Papers - OSADA Minoru

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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

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

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

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

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

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

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

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

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

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

APPLIED PHYSICS LETTERS Vol. 97 ( 18 ) 2010.11

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

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

JOURNAL OF APPLIED PHYSICS Vol. 108 ( 10 ) 2010.11

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

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

APPLIED PHYSICS LETTERS Vol. 97 ( 18 ) 2010.11

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

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 118 ( 1382 ) page： 955 - 958 2010.10

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

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

ACS NANO Vol. 4 ( 9 ) page： 5225 - 5232 2010.9

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

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

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

JOURNAL OF APPLIED PHYSICS Vol. 108 ( 6 ) 2010.9

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

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

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

APPLIED PHYSICS LETTERS Vol. 97 ( 11 ) 2010.9

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

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

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

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 118 ( 1381 ) page： 814 - 818 2010.9

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

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