IMRAM

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University

東北大学
多元物質科学研究所

LAST UPDATE 2021/05/06

  • 研究者氏名
    Researcher Name

    森川大輔　Daisuke MORIKAWA
    助教　Assistant Professor

  • 所属
    Professional Affiliation

    東北大学多元物質科学研究所
    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University

    計測研究部門
    Division of Measurements

  • 研究キーワード
    Research Keywords

    電子顕微鏡法
    収束電子回折法
    結晶構造解析
    Transmission electron microscopy
    Convergent-beam electron diffraction
    Crystal structure analysis
研究テーマ
Research Subject
収束電子回折法を用いた局所構造解析手法の開発と界面やその場観察への応用
Local structure analysis applied for interface and in-situ experiment using convergent-beam electron diffraction

研究の背景 Background

透過型電子顕微鏡(TEM)はナノメータスケールの微小領域の解析が可能な強力な装置です．また電子回折実験では，レンズによる収差の影響がほぼないことから，従来のイメージングによる分解能を越える解析が可能です．特に収束電子回折法は，電子線の多重散乱の効果をフルに活用することで，ほとんどの空間群を一意に決定できる他，価電子分布に敏感な静電ポテンシャル分布を直接決定できることから，わずかな電子雲のズレや結合などの検出が可能であると期待されています．

Transmission electron microscopy (TEM) is a powerful tool for an analysis in nano-scale specimen areas. Electron diffraction using a TEM is not almost affected by aberrations come from lens system. Thus, it is possible to achieve higher resolution than conventional imaging techniques. Especially, convergent-beam electron diffraction (CBED) can determine almost all crystal space group uniquely using dynamical scattering effect. CBED can be also used for a determination of electrostatic potential which is sensitive for slight deviation on electron density and bonding state at valence electrons.

研究の目標 Outcome

電子顕微鏡のマイクロスコピー機能との併用により，ナノメータスケールでの精密構造解析を目指します．特に結晶界面や粒界近傍等の微小領域の解析[1]に有用で，分極ナノドメインの電圧印加その場観察[2]も可能です．現在，第一原理計算との組み合わせによる新しい局所領域構造解析，物性解析手法の開発[3]に取り組んでいます．さらに機械学習を応用した2次元的な結晶情報のマッピングや，ソフトマテリアルへの応用にも挑戦してまいります．

By using a combination with microscopy in TEM, we develop an accurate crystal structure analysis method for nano-scale specimen area. CBED method is a very powerful and useful technique for analysis in interfaces of crystal [1] and grain boundaries and in-situ observation of polar nano domains under electric field [2]. We are also trying a development of new technique with a combination of CBED and first principal calculation [3]. Two-dimensional mapping of crystal information with using machine-learning and applications for soft materials are also future targets.

研究図Research Figure

Fig.1. (a) Reconstructed scanning transmission electron microscopy image formed by summing the intensities at the position indicated by the red circle in (b)(1). The STEM image was reconstructed from 40×3 CBED patterns. (b) CBED patterns obtained for the positions shown in (a)(1)– (9). The letter “m” denotes mirror symmetry. Position 5 corresponds to a twin boundary. (c) CBED pattern obtained at a twin boundary using an exposure time of 10 s and the conventional CBED mode. (d), (e), and (f) are as for (a), (b), and (c), respectively, but for a different part of the specimen. [1]

Fig.2. (a)–(k) Symmetry-breaking index map at different applied electric-fields. The arrows indicate the mesoscopic polarization direction. The bright area shows the areas of a lower index, and it implies higher tetragonal symmetry for mirror operation. (l)–(o) CBED patterns obtained at the red points shown in (a)–(d). The CBED pattern shown in (l) shows tetragonal symmetry breaking as indicated by arrowheads, while the CBED patterns of (m)–(o) under an applied electric-field are seen to have almost tetragonal symmetry. [2]

文献 / Publications

[1] D. Morikawa and K. Tsuda, Appl. Phys. Lett. 118, 092901 (2021).
[2] D. Morikawa and K. Tsuda, Appl. Phys. Lett. 119, 052904 (2021).
[3] Md S. Islam, D. Morikawa, S. Yamada, B. Aryal, K. Tsuda, and M. Terauchi, Phys. Rev. B 105, 174114 (2022).

研究者HP