Liquid Cell Transmission Electron Microscopy Study of Platinum Iron Nanocrystal Growth and Shape Evolution

We
study solution growth of platinum iron nanocrystals in situ
in a liquid cell by using transmission electron microscopy. By varying
the oleylamine concentration, we observed that platinum iron nanoparticle
growth follows different trajectories with diverse shape evolution.
With 20% oleylamine, three stages of growth were observed: (i) nucleation
and growth of platinum iron nanoparticles in the precursor solution;
(ii) nanowire formation by shape-directed nanoparticle attachment;
and (iii) breakdown or shrinkage of the nanowires into individual
nanoparticles with large size distribution. With 30% oleylamine, formation
of platinum iron nanowires similar to that with 20% oleylamine was
observed. However, those nanowires do not break down or shrink, which
suggests that nanowires are stabilized by oleylamine as surfactant
binding on the surface. With 50% oleylamine, after the individual
nanoparticles are formed, they do not merge into nanowires. The shape
of the nanoparticle is strongly influenced by the neighboring nanoparticles
due to stereo-hindrance effects. Real-time observation of the dynamic
growth process sheds light on the controllable synthesis of nanomaterials.