In Situ Electron Microscopy Study on Surface Etching/Growth Kinetics of Bi ₂ Se ₃ Nanosheets

A thorough understanding of Bi₂Se₃ surface etching is crucial for elucidating mechanisms, precise surface function adjustment, and advancing optoelectronic/catalytic applications, as this typical topological insulator has unique surface-dependent properties. However, the dynamic etching mechanisms essential for functionality tuning remain poorly understood due to conventional technique limitations. Here, in situ transmission electron microscopy (TEM) and liquid cell electron microscopy techniques (LC-TEM/LC-SEM) were employed to track Bi₂Se₃ etching kinetics in vacuum and liquid environments. It was suggested that electron-beam irradiation effectively promotes the evolution of the inherent void defect within the Bi₂Se₃ material. In the liquid phase, a high electron dose rate (25 e/(Ų·s)) not only triggers the etching of Bi₂Se₃ nanosheets but also promotes the precipitation of bismuth(III) compounds. Both the chemical blocking effect of the potential surface oxide layer and the structural defect characteristics of the screw dislocations significantly influence etching site selection (>80% etching ratio at edges vs <20% at corners). High temporal resolution (0.25 s per frame) in situ LC-SEM studies of bubble boundary and particle motion revealed that liquid layer dynamics significantly impact the imaging performance. Notably, these mechanistic findings provide a rational pathway for precisely regulating the surface structure of Bi₂Se₃ and analogous layered topological insulators, which is pivotal for optimizing the performance of next-generation optoelectronic devices and heterogeneous catalysts. This work further helps to elucidate the universal mechanisms of oxidative etching of layered nanomaterial surfaces.