Faculty Profiles - OSADA Minoru

Papers - OSADA Minoru

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Layer-by-layer engineering of two-dimensional perovskite nanosheets for tailored microwave dielectrics Reviewed

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

APPLIED PHYSICS EXPRESS Vol. 10 ( 9 ) 2017.9

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

Web of Science

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

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

CHEMISTRYSELECT Vol. 2 ( 24 ) page： 6941 - 6944 2017.8

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

Web of Science

Atomic Layer Engineering of High-kappa Ferroelectricity in 2D Perovskites Reviewed

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

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Vol. 139 ( 31 ) page： 10868 - 10874 2017.8

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

Web of Science

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

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

APL MATERIALS Vol. 5 ( 7 ) 2017.7

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

Web of Science

High-temperature dielectric responses in all-nanosheet capacitors Reviewed

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

Japanese Journal of Applied Physics Vol. 56 ( 6 ) 2017.6

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

Web of Science

Scopus

Neat monolayer tiling of molecularly thin two-dimensional materials in 1 min Reviewed

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

SCIENCE ADVANCES Vol. 3 ( 6 ) 2017.6

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

Web of Science

Ferroelectric BaTiO3 dipole induced charge transfer enhancement in dye-sensitized solar cells Reviewed

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

JOURNAL OF POWER SOURCES Vol. 350 page： 35 - 40 2017.5

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

Web of Science

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

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

NPG ASIA MATERIALS Vol. 9 2017.2

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

Web of Science

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

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

Scientific Reports Vol. 7 page： 3630 2017

Neat monolayer tiling of molecularly thin two-dimensional materials in one minute Reviewed

Vol. 3 page： e1700414 2017

Atomic layer engineering of high-k ferroelectricity in 2D perovskites Reviewed

Vol. 139 page： 10868-10874 2017

Advanced capacitor technology based on two-dimensional nanosheets Reviewed

Hyung-Jun Kim, Minoru Osada, Takayoshi Sasaki

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 55 ( 11 ) 2016.11

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

Web of Science

Highly (0001)-oriented Al-doped ZnO polycrystalline films on amorphous glass substrates Reviewed

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

JOURNAL OF APPLIED PHYSICS Vol. 120 ( 12 ) 2016.9

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

Web of Science

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

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

JOURNAL OF LUMINESCENCE Vol. 173 page： 130 - 134 2016.5

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

Web of Science

Thermally stable dielectric responses in uniaxially (001)-oriented CaBi4Ti4O15 nanofilms grown on a Ca2Nb3O10- nanosheet seed layer Reviewed

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 Vol. 6 2016.2

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

Web of Science

Influences of high deposition rate on LiCoO2 epitaxial films prepared by pulsed laser deposition Reviewed

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

SOLID STATE IONICS Vol. 285 page： 91 - 95 2016.2

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

Web of Science

Coexistence of magnetic order and ferroelectricity at 2D nanosheet interfaces Reviewed

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

J. Am. Chem. Soc. Vol. 138 page： 7621-7625 2016

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 Vol. 10 page： 1655-1661 2016

Hunting for monolayer oxide nanosheets and their architectures

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

Scientific Reports Vol. 6 page： 19402-1 2016

Thermoresponsive actuation enabled by permittivity switching in an electrostatically anisotropic hydrogel Reviewed

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

NATURE MATERIALS Vol. 14 ( 10 ) page： 1002 - 1007 2015.10

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

Web of Science

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Papers - OSADA Minoru