Growth of Colloidal Nanocrystals by Liquid-Like Coalescence*

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth

Metal nanocrystals (NCs) produced by colloidal synthesis have a variety of structural features, such as different planes, edges, and defects. Even from the best colloidal syntheses, these characteristics are distributed differently in each NC. This inherent heterogeneity can play a significant role in the properties displayed by NCs. This manuscript reports the use of electrochemistry to synthesize Au NCs in a system evaluated to track individual NC growth trajectories as a first step toward rapid identification of NCs with different structural features. Au nanocubes were prepared colloidally and deposited onto a glassy carbon electrode using either electrospray or an airbrush, resulting in well-spaced Au nanocubes. The Au nanocubes then served as seeds as gold salt was reduced to deposit metal at constant potential. Deposition at constant potential facilitates overgrowth on the Au nanocubes to achieve new NC shapes. The effects of applied potential, deposition time, precursor concentration, and capping agents on NC shape evolution were studied. The outcomes are correlated to results from traditional colloidal syntheses, providing a bridge between the two synthetic strategies. Moreover, scanning electron microscopy was used to image the same NCs before and after deposition, linking individual seed features to differences in deposition. This ability is anticipated to enable tracking of individual growth trajectories of NCs to elucidate sources of heterogeneity in NC syntheses.

Identification of plasmon-driven nanoparticle-coalescence-dominated growth of gold nanoplates through nanopore sensing

The fascinating phenomenon that plasmon excitation can convert isotropic silver nanospheres to anisotropic nanoprisms has already been developed into a general synthetic technique since the discovery in 2001. However, the mechanism governing the morphology conversion is described with different reaction processes. So far, the mechanism based on redox reactions dominated anisotropic growth by plasmon-produced hot carriers is widely accepted and developed. Here, we successfully achieved plasmon-driven high yield conversion of gold nanospheres into nanoplates with iodine as the inducer. To investigate the mechanism, nanopore sensing technology is established to statistically study the intermediate species at the single-nanoparticle level. Surprisingly, the morphology conversion is proved as a hot hole-controlled coalescence-dominated growth process. This work conclusively elucidates that a controllable plasmon-driven nanoparticle-coalescence mechanism could enable the production of well-defined anisotropic metal nanostructures and suggests that the nanopore sensing could be of general use for studying the growth process of nanomaterials.