研究者詳細 - 長田　実

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