Atomic-Scale In Situ Scanning Transmission Electron Microscopy of MoS during Lithiation.

Atomic-scale in situ characterization techniques are necessary to clarify the dynamic local structural changes during intercalation reactions. High-resolution transmission electron microscopy (HRTEM) is at the forefront of this field. However, the image contrast in HRTEM is not always straightforward, necessitating the exploration of alternative imaging techniques. Here, using annular dark-field (ADF) scanning transmission electron microscopy (STEM), which is expected to provide a more directly interpretable image contrast, we report atomic-scale in situ observation of the MoS lithiation process induced by electron irradiation. Using a single-crystalline specimen, dedicated specimen holder, and alternate low- and high-magnification image acquisition technique, a time series of ADF-STEM images was recorded at a frame rate of 1 fps, followed by image filtering. Consequently, successive changes in the domain structure were clarified, starting with an anisotropically expanding structural phase transition, followed by the disappearance and formation of domains with different crystal orientations, which were attributed to changes in the internal stress and interfacial energy.