Windowless Observation of Evaporation-Induced Coarsening of Au-Pt Nanoparticles in Polymer Nanoreactors

TL;DR

This study introduces a windowless, polymer nanoreactor system to observe Au-Pt nanoparticle coarsening during solvent evaporation, revealing the influence of polymer edges and solvent dynamics on nanoparticle behavior.

Contribution

It demonstrates a novel windowless approach to study nanoparticle coarsening, providing new insights into solvent effects and particle formation mechanisms during nanostructure synthesis.

Findings

Polymer edge evaporation accelerates nanoparticle coalescence.

Capillary forces from polymer edges influence nanoparticle dynamics.

Traditional coarsening models are inadequate for thin film solvent systems.

Abstract

The interactions between nanoparticles and solvents play a critical role in the formation of complex, metastable nanostructures. However, direct observation of such interactions with high spatial and temporal resolution is challenging with conventional liquid-cell transmission electron microscopy (TEM) experiments. Here, a windowless system consisting of polymer nanoreactors deposited via scanning probe block copolymer lithography (SPBCL) on an amorphous carbon film is used to investigate the coarsening of ultrafine (1-3 nm) Au-Pt bimetallic nanoparticles as a function of solvent evaporation. In such reactors, homogeneous Au-Pt nanoparticles are synthesized from metal ion precursors in situ under electron irradiation. The non-uniform evaporation of the thin polymer film not only concentrates the nanoparticles, but also accelerates the coalescence kinetics at the receding polymer edges. Qualitative analysis of the particle forces influencing coalescence suggests that capillary dragging by the polymer edges plays a significant role in accelerating this process. Taken together, this work: 1) provides fundamental insight into the role of solvents in the chemistry and coarsening behavior of nanoparticles during the synthesis of polyelemental nanostructures, 2) provides insight into how particles form via the SPBCL process, and 3) shows how SPBCL-generated domes, instead of liquid cells, can be used to study nanoparticle formation. More generally, it shows why conventional models of particle coarsening, which do not take into account solvent evaporation, cannot be used to describe what is occurring in thin film, liquid-based syntheses of nanostructures.