Atomic mechanisms of hexagonal close-packed Ni nanocrystallization revealed by in situ liquid cell transmission electron microscopy

The fundamental understanding of the mechanism underlying the early stages of crystallization of hexagonal-close-packed (hcp) nanocrystals is crucial for their synthesis with desired properties, but it remains a significant challenge. Here, we report using in situ liquid cell transmission electron microscopy (TEM) to directly capture the dynamic nucleation process and track the real-time growth pathway of hcp Ni nanocrystals at the atomic scale. It is demonstrated that the growth of amorphous-phase-mediated hcp Ni nanocrystals is from the metal-rich liquid phases. In addition, the reshaped preatomic facet development of a single nanocrystal is also imaged. Theoretical calculations further identify the non-classical features of hcp Ni crystallization. These discoveries could enrich the nucleation and growth model theory and provide useful information for the rational design of synthesis pathways of hcp nanocrystals.