SEM as a Facile Tool for Real-Time Monitoring of Microcrystal Growth during Electrodeposition: The Merit of Ionic Liquids.

Due to the extremely low vapor pressure of ionic liquids (ILs), electrochemical deposition/dissolution of hexagonal hollow CuSn alloy tubes in IL can be real-time observed with a scanning electron microscope (SEM). Two specially made electrochemical cells are used for the top-view and side-view observations. A series of clear SEM images reveals the hexagonal cones are formed prior to further developing hexagonal tubes. At the beginning, many small nuclei are formed on the electrode surface. Due to the electrodeposition rate being slow enough for the nuclei to crystallize into hexagonal structures, the electrodeposition rate is faster on the periphery than the inside of the structures. As the electrodeposition progresses, the tube wall will grow thicker, and a secondary tube emerges inside the primary tube. Finally, shell-by-shell hexagonal tubes are formed. Furthermore, the in situ SEM observation also reveals that the dissolution of tube starts from its inner wall followed by a sudden collapse of its wall. In this paper, we establish a simple and convenient method, which can be broadly applied to the study of metal, alloy, and semiconductor growth in real time.