In Situ TEM Observation of Phase Transformation Nucleation at the Near-Surface of Synthetic Aragonite

Electron beam irradiation is well known to induce damage to materials during transmission electron microscope (TEM) characterization, especially for insulating materials. Phase transformation is an important damage phenomenon caused by beam irradiation. Here, we employed in situ TEM combined with electron-energy loss spectroscopy (EELS) to dynamically track the phase transformation of synthetic aragonite. The evolution process and underlying mechanism of the phase transformation in aragonite are systematically discussed. This work reveals that the near-surface region of aragonite undergoes a phase transformation induced by electron beam irradiation, prior to the bulk of aragonite. It provides more possibilities for searching the multiple near-surface properties of materials. Highlights The TEM and EELS are used to track the near-surface phase transformation in synthetic aragonite. The near-surface is easily changed compared with the bulk part of aragonite under electron beam irradiation. The mechanism of beam damage in the near-surface region is the result of the combined effect of knock-on displacement and radiolysis, whereas the bulk region undergoes phase transformation due to radiolysis. The phenomenon that the bulk is more severely damaged at the periphery of electron beam is attributed to the DIEF mechanism.