Segawa Yuhiro, Yamazaki Kenji, Yamasaki Jun, Gohara Kazutoshi
Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan.
Nanoscale. 2021 Mar 21;13(11):5847-5856. doi: 10.1039/d1nr00237f. Epub 2021 Mar 15.
Free-standing graphene has a three-dimensional (3D) structure, called a ripple, rather than a perfect two-dimensional (2D) crystal. Since theoretical calculations suggest that a ripple strongly influences various fundamental physicochemical properties of graphene, it is important to clarify the ripple structure quantitatively in experiments. This paper proposes a new method of measuring the 3D atomic structure of a ripple by using aberration-corrected transmission electron microscopy (TEM). The method utilizes the fact that the 2D contrast of a TEM image is sensitive to the height of a six-membered ring. The proposed method is experimentally applied to a monolayer graphene, and the 3D atomic arrangements of consecutively acquired TEM images are reconstructed. In that experiment, the specimen is found to be moving upward. Furthermore, the atomic arrangement can be approximated as a composite of two structures consisting of a 3D ripple and a 2D plane. The ripple is represented as a superposition of sinusoidal waves, with their wave vectors coinciding with the specific direction of the six-membered ring. The time dependences of the height and lateral size of the ripple are also measured.
独立的石墨烯具有一种三维（3D）结构，称为波纹，而不是完美的二维（2D）晶体。由于理论计算表明，波纹会强烈影响石墨烯的各种基本物理化学性质，因此在实验中定量阐明波纹结构非常重要。本文提出了一种使用像差校正透射电子显微镜（TEM）测量波纹三维原子结构的新方法。该方法利用了TEM图像的二维对比度对六元环高度敏感这一事实。所提出的方法在实验中应用于单层石墨烯，并重建了连续获取的TEM图像的三维原子排列。在该实验中，发现样品在向上移动。此外，原子排列可以近似为由三维波纹和二维平面组成的两种结构的组合。波纹表示为正弦波的叠加，其波矢与六元环的特定方向一致。还测量了波纹高度和横向尺寸的时间依赖性。
