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.