Faculty Profiles - OSADA Minoru

Papers - OSADA Minoru

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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

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

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

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

Lithium silicon sulfide as an anode material in all-solid-state lithium batteries Reviewed

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

JOURNAL OF POWER SOURCES Vol. 195 ( 10 ) page： 3323 - 3327 2010.5

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

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

APPLIED PHYSICS LETTERS Vol. 96 ( 18 ) 2010.5

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

Engineered interfaces of artificial perovskite oxide superlattices via nanosheet deposition process Reviewed

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

ACS Nano Vol. 4 page： 6673-6680 2010

Robust high-k response in molecularly thin perovskite nanosheets Reviewed

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

ACS Nano Vol. 4 page： 5225-5232 2010

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

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 Vol. 49 ( 9 ) 2010

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

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

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 113 ( 44 ) page： 19096 - 19101 2009.11

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

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

JOURNAL OF MATERIALS SCIENCE Vol. 44 ( 19 ) page： 5339 - 5344 2009.10

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

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

CHEMISTRY OF MATERIALS Vol. 21 ( 19 ) page： 4366 - 4373 2009.10

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

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 Vol. 48 ( 9 ) 2009.9

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

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

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 48 ( 9 ) 2009.9

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

Yoshihiro Takahashi, Hirokazu Masai, Minoru Osada, Takumi Fujiwara

APPLIED PHYSICS LETTERS Vol. 95 ( 7 ) 2009.8

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

Yoshihiro Takahashi, Minoru Osada, Hirokazu Masai, Takumi Fujiwara

APPLIED PHYSICS LETTERS Vol. 94 ( 24 ) 2009.6

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

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