Real-time imaging of metallic supraparticle assembly during nanoparticle synthesis

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Conventional self-assembly models require extended times for nanoparticle superlattice formation, relying on diffusion-driven annealing of defects.
• The rapid kinetics of superlattice growth observed in some syntheses conflict with these models, leaving the mechanism for rapid annealing unclear.

Purpose of the Study:

• To directly observe and elucidate the mechanism of rapid nanoparticle superlattice formation during synthesis.
• To reconcile the observed fast kinetics with established theories of self-assembly.

Main Methods:

• Utilized in-situ liquid phase transmission electron microscopy (LPTEM) to image the dynamic self-assembly process.
• Synthesized 2-3 nm platinum nanoparticles via electron-beam induced reduction.
• Varied precursor chemistry to tune interparticle interactions (electrostatic, steric).

Main Results:

• Direct imaging revealed simultaneous nanoparticle formation and self-assembly into 3D supraparticles within tens of seconds.
• Observed crystalline ordered domains within the rapidly formed supraparticles.
• Identified weak van der Waals forces balanced by short-range steric repulsion as key drivers of assembly.
• Demonstrated that nanoparticle surface diffusion rates significantly exceed attachment rates.

Conclusions:

• Nanoparticle surface diffusion is orders of magnitude faster than attachment, allowing rapid annealing of defects.
• This rapid annealing reconciles fast supraparticle formation with conventional self-assembly paradigms.
• The findings provide a new understanding of self-assembly mechanisms under rapid synthesis conditions.