Abstract
The understanding of crystal growth mechanisms has broadened substantially. One significant advancement is based in the conception that the interaction between particles plays an important role in the growth of nanomaterials. This is in contrast to the classical model, which neglects this process. Direct imaging of such processes at atomic-level in liquid-phase is essential for establishing new theoretical models that encompass the full complexity of realistic scenarios and eventually allow for tailoring nanoparticle growth. Here, we investigate at atomic-scale the exact growth mechanisms of platinum nanocrystals from single atom to final crystals by in-situ liquid phase scanning transmission electron microscopy. We show that, after nucleation, the nanocrystals grow via two main stages: atomic attachment in the first stage, where the particles initially grow by attachment of the atoms until depletion of the surrounding zone. Thereafter, follows the second stage of growth, which is based on particle attachment by different atomic pathways to finally form mature nanoparticles. The atomic mechanisms underlying these growth pathways are distinctly different and have different driving forces and kinetics as evidenced by our experimental observations.
Highlights
The understanding of crystal growth mechanisms has broadened substantially
We demonstrate that using graphene liquid cells (GLCs) combined with aberration-corrected scanning transmission electron microscopy (TEM) (STEM) with a fast acquisition strategy substantially improves the spatial and temporal resolutions for reactions in liquid phase and allows us to study the exact growth mechanisms of Pt nanoparticles at the atomic-level from metastable states to final crystals
In comparison to the previous studies of growth mechanisms using in situ TEM, our study focuses at atomic scale on the intermediate steps in both first and second stage of the multi-step growth mechanisms
Summary
We use 5 mM aqueous solution of Na2PtCl4·2H2O to study nucleation and growth of Pt nanoparticles. This second particle will be important to document the second stage in the growth process. After attachment of the smaller particles, the larger particle starts a relaxation process to remove the defective areas, until a perfect monocrystalline nanoparticle is established (Fig. 4a at t = 300 s) as confirmed by the inset FT showing consistent sharp spots It appears that, under the present experimental conditions, structural rearrangements of the nanocrystal after imperfect attachment occurred via surface rearrangements and via reorganization of the complete nanocrystal interior. Our study provides an in-depth insight into nanomaterial synthesis for the particular system investigated
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