Atomic Investigation on the Facet‐Dependent Melting of Ceramic Nanostructures via In Situ Electron Irradiation

Abstract Thermodynamic behavior investigations on nanomaterials are of great scientific interest and possess technological implications for advancing nanoscience and nanotechnology. However, nanoscale thermodynamic studies on ceramic semiconductors are faced with great challenges due to their thermostability, and there lacks a percipient understanding of their atomistic thermal behaviors. Here, the atomic‐scale mechanism of the melting and coalescence processes of binary semiconductors, including rutile TiO₂(R) and SnSe nanostructures, via real‐time electron beam (e‐beam) irradiation is reported. Under the e‐beam, the inelastic electron‐matter interactions and the low thermal conductivity of the samples cause a local temperature increase. The in situ melting process is recorded via high‐resolution TEM imaging, which exclusively shows a specific planar melting order of the (001), (011), and (100) for TiO₂(R). This measurement provides direct evidence that matches the surface energy differences predicted by existing theoretical calculations and experiments. A similar phenomenon is induced and observed on SnSe, which derives a particular melting order of (210), (211), and (002). Furthermore, the in situ melting and coalescence analysis of ultrafine TiO₂(R) nanoparticles suggests surface atom transfer and recrystallization as observed. The demonstration of e‐beam directed shape formation and tailoring reveals the possibility for nano/microscale processing of ceramic nanostructures, which are otherwise considered chemically stable and mechanically robust.