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.

Visualizing the crystallization of sodium chloride under supersaturated condition

Crystallization in supersaturated solution plays a fundamental role in a variety of natural and industrial processes.However,a thorough understanding of crystallization phenomena in supersaturated solution is still difficult because the real-time visualization of crystallization processes under supersaturated condition is a great challenge.Herein,an electron beam-induced crystallization method was carried out in in situ liquid cell transmission electron microscopy(TEM)to visualize the crystallization of NaCl under supersaturated condition in real time.Crucial steps and behaviors in the crystallization of NaCl were captured and clarified,including the growth of NaCl nanocrystals with different morphologies,the formation of initial crystalline seeds from amorphous ion clusters,and the non-equilibrium growth behaviors caused by uneven distribution of precursor ions.This study provides the real-time visualization of detailed nucleation and growth behaviors in NaCl crystallization and brings an ideal strategy for investigating crystallization phenomena under supersaturated condition.

Real time imaging of two-dimensional iron oxide spherulite nanostructure formation

The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view.Spherulite structures with radial fibrillar branches have been found in various solids;however,their growth mechanisms remain poorly understood.Here,we report real time imaging of the formation of two-dimensional(2D)iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy(TEM).By tracking the growth trajectories,we show the characteristics of the reaction front and growth kinetics.Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes(5.5–8.5 nm).The radius of a spherulite nanostructure increases linearly with time at the early stage,transitioning to nonlinear growth at the later stage.Furthermore,a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches.The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth.A growth model is further established,which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth.