Browsing by Author "Xu, Jun"

Now showing 1 - 2 of 2

In Situ Study of Fe3Pt-Fe2O3 Core-Shell Nanoparticle Formation
(2015-12-02)
Liang, Wen-I
;
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.
In Situ Study of Spinel Ferrite Nanocrystal Growth Using Liquid Cell Transmission Electron Microscopy
(2015-12-08)
Liang, Wen-I
;
Zhang, Xiaowei
;
Bustillo, Karen
;
Chiu, Chung-Hua
;
Wu, Wen-Wei
We report transition metal oxide nanocrystal formation in a liquid cell using. transmission electron microscopy (TEM). The growth of M-Fe-oxide (M = Ni, Mn, Co, or Zn) nanoparticles from a growth solution of metal acetylacetonates dissolved in oleylamine, oleic acid, and benzyl ether was studied. Nickel iron oxide nanocrystals with spinel structure were obtained under electron beam irradiation of the Ni-Fe growth solution, whereas iron oxide nanocrystals were achieved with Mn remaining in the Mn-Fe growth solution. Similarly, we achieved cobalt iron oxide nanocrystals in the Co-Fe precursor solution, while iron oxide nanoparticles were obtained in the Zn-Fe solution. By tracking nanoparticle size evolution as a function of time along the Ni-Fe oxide nanoparticle growth trajectories, we found the growth kinetics follow a Lifshitz-Slyozov-Wagner (LSW) model suggesting surface reaction-limited growth. Ex situ characterization shows elemental distribution and structural and valence state of the different nanoparticles. The trend of nanoparticle growth in a liquid cell shares many similarities with those in "one-pot" flask synthesis by thermal heating. We compare reduction potentials (E-r) of the metal ions and thermal decomposition temperatures (T-d) of the precursors and correlate them with nanoparticle growth in a liquid cell under TEM. We found a tendency to form mixed metal ion oxide nanoparticles instead of single metal ion (iron) oxides when the two precursors have similar values of T-d and metal ion reduction potential. The higher T-d and smaller E-r values of Mn and Zn precursors than those of Fe precursor, as well as Ni and Co precursors, may have resulted in the single metal ion (iron) oxide formation in M-Fe (M = Mn and Zn) precursor systems. This study sheds light on nanoparticle growth mechanisms by liquid cell TEM. In situ study of oxide nanocrystal growth using liquid cell TEM provides the opportunity to explore solution chemistry during nanocrystal growth beyond the nanoparticle growth that occurs in a TEM cell.