[M-IS12] Interface- and nano-phenomena on crystal growth and dissolution

[MIS12-02] Dielectrophoresis of submicron-sized particles in liquid-cell transmission electron microscopy

*Tomoya Yamazaki¹, Hiromasa Niinomi², Hiroyasu Katsuno¹, Yuki Kimura¹ (1.Institute of Low Temperature Science Hokkkaido University, 2.Institute of Multidisciplinary Research of Advanced Materials)

Keywords:liquid-cell transmission electron microscopy, dielectrophoresis, electric field, particle assembly, crystallization, solution

Liquid-cell transmission electron microscopy (LC-TEM) is a technique for TEM observation of a liquid sample, which can be achieved by sandwiching the liquid sample with thin films and keeping it isolated from the high vacuum environment. This technique can realize nanoscale observation, although its spatial resolution is most limited by the thickness of the liquid layer. Furthermore, by using a camera with high sensitivity and high temporal resolution, it is possible to make continuous observations in sub-second or less. Therefore, in situ observation of phenomena in a liquid sample and clarification of their dynamic behavior can help us understand them. In particular, it is expected to reveal phenomena related to crystallization that has been difficult to observe so far, such as nucleation. In general, in order to capture the moment of nucleation, a condition of high supersaturation is required, and nucleation must occur in the field of view where we are observing. However, in LC-TEM, it is still difficult to achieve a condition of high supersaturation in the field of view. To solve this issue, we focused on dielectrophoresis, in which particles can be assembled locally by an electric field gradient around electrodes. If this phenomenon can be effectively utilized in LC-TEM, it may be possible to increase the local concentration of particles and promote crystallization. In our previous report, we showed that dielectrophoresis could be observed in LC-TEM using an existing liquid cell equipped with an electrode. However, because the electric field gradient formed around the electrode was weak, the particles could not be assembled efficiently in LC-TEM. Here we have newly designed and developed a device for the liquid cell that can achieve the high electric field gradient. Using this device and sub-micron size particles, we succeeded in capturing the assembly of particles by LC-TEM. Based on the observation results, we will discuss the properties of the assembled particles and the usefulness of dielectrophoresis in LC-TEM.

Acknowledgements
This work was supported partly by the GIMRT Program of the Institute for Materials Research, Tohoku University (Proposal No. 20K0038) and JSPS KAKENHI Grant Numbers 20H02580 and 20H05657.