Browsing by Author "Pan, Ming"

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Dynamics of Nanoscale Dendrite Formation in Solution Growth Revealed Through in Situ Liquid Cell Electron Microscopy
(2018-10-01)
Hauwiller, Matthew R.
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Zhang, Xiaowei
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Liang, Wen-I
;
Chiu, Chung-Hua
;
Zhang, Qian
Formation mechanisms of dendrite structures have been extensively explored theoretically, and many theoretical predictions have been validated for micro- or macroscale dendrites. However, it is challenging to determine whether classical dendrite growth theories are applicable at the nanoscale due to the lack of detailed information on the nanodendrite growth dynamics. Here, we study iron oxide nanodendrite formation using liquid cell transmission electron microscopy (TEM). We observe "seaweed"-like iron oxide nanodendrites growing predominantly in two dimensions on the membrane of a liquid cell. By tracking the trajectories of their morphology development with high spatial and temporal resolution, it is possible to explore the relationship between the tip curvature and growth rate, tip splitting mechanisms, and the effects of precursor diffusion and depletion on the morphology evolution. We show that the growth of iron oxide nanodendrites is remarkably consistent with the existing theoretical predictions on dendritic morphology evolution during growth, despite occurring at the nanoscale.
In Situ Study of Fe3Pt-Fe2O3 Core-Shell Nanoparticle Formation
(2015-12-02)
Liang, Wen-I
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Zhang, Xiaowei
;
Zan, Yunlong
;
Pan, Ming
;
Czarnik, Cory
We report an in situ study of Fe3Pt-Fe2O3 coreshell nanoparticle growth using liquid cell transmission electron microscopy. By controlling the Fe-to-Pt ratio in the precursor solution, we achieved the growth of nanoparticles with the formation of an ironplatinum alloy core followed by an iron oxide shell in the electron beam-induced reactions. There was no substantial change in the growth kinetics of the iron oxide shell after the FePt alloy core stopped growing. The core growth was arrested by depletion of the Pt precursor. Heteroepitaxy of Fe3Pt [101] (core)||alpha-Fe2O3 [111] (shell) was observed in most of the nanoparticles, while a polycrystalline iron oxide shell is developed eventually for strain relaxation. Our studies suggest that Pt atoms catalyze the reduction of Fe ions to form the Fe3Pt alloy core, and when Pt is depleted, a direct precipitation of iron oxide results in the core-shell nanostructure formation.