Institute of Multidisciplinary Research for Advanced Materials, Tohoku University


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

    Institute of Multidisciplinary Research for Advanced Materials, Tohoku University

    Division of Measurements
  • 研究キーワード
    Research Keywords

    Transmission electron microscopy
    Convergent-beam electron diffraction
    Crystal structure analysis
Research Subject
Local structure analysis applied for interface and in-situ experiment using convergent-beam electron diffraction

研究の背景 Background


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


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).