Exploring the Formation of Symmetric Gold Nanostars by Liquid-Cell Transmission Electron Microscopy

Babeel Ahmad, Guillaume Wang, Jaysen Nelayah, Christian Ricolleau and Damien Alloyeau, 2017
sequential micrographs and illustrations of gold nanostar formation
Image courtesy of Nano Letters

Abstract

The shape-dependent properties of gold nanostars (NSs) have motivated massive research efforts in the field of colloidal chemistry to gain a better control over the morphology of these promising nanostructures. Nevertheless, this challenge requires a better understanding of the atomic-scale processes leading to the formation of stellated nanoparticles. We hereby report an unprecedented in situ study focused on the seed-mediated synthesis of symmetric gold NSs performed by radiolysis in methanol. We take advantage of the spatial and temporal resolutions of liquid-cell transmission electron microscopy to unravel the key effects of the growth speed, seed-crystal morphology, and dimethylamine functionalization on the formation mechanisms, shape, and stability of NSs enclosed by high-index facets. Surprisingly, the stellation processes transforming icosahedral nanoparticles into NSs with 20 sharp arms entails a continuous restructuring of NS facets driven by surface diffusion, which provide a fresh look at faceting mechanisms.

Impact Statement

The growth mechanism of gold nanostars via a two-step electron beam induced reduction process was studied in situ using LC-TEM. Highly faceted gold seed precursors are initially formed by exposing a liquid cell containing a mixture of HAuCL4 and methanol to the electron beam. Next, with the beam off, a solution containing dimethylamine was flowed through the holder and allowed to equilibrate for thirty minutes, after which the electron beam was again used to initiate and monitor the growth process.