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.
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.