Quantitative In Situ Visualization of Thermal Effects on the Formation of Gold Nanocrystals in Solution

Abstract

Understanding temperature effects in nanochemistry requires real‐time in situ measurements because this key parameter of wet‐chemical synthesis simultaneously influences the kinetics of chemical reactions and the thermodynamic equilibrium of nanomaterials in solution. Here, temperature‐controlled liquid cell transmission electron microscopy is exploited to directly image the radiolysis‐driven formation of gold nanoparticles between 25 °C and 85 °C and provide a deeper understanding of the atomic‐scale processes determining the size and shape of gold colloids. By quantitatively comparing the nucleation and growth rates of colloidal assemblies with classical models for nanocrystal formation, it is shown that the increase of the molecular diffusion and the solubility of gold governs the drastic changes in the formation dynamics of nanostructures in solution with temperature. In contraction with the common view of coarsening processes in solution, it is also demonstrated that the dissolution of nanoparticles and thus the Ostwald ripening is not only driven by size effects. Furthermore, visualizing thermal effects on faceting processes at the single nanoparticle level reveals how the competition between the growth speed and the surface diffusion dictates the final shape of nanocrystals.

Radiolysis‐Driven Evolution of Gold Nanostructures – Model Verification by Scale Bridging In Situ Liquid‐Phase Transmission Electron Microscopy and X‐Ray Diffraction

“…Moreover, an overview of reports describing evolution of gold nanostructures from pristine HAuCl 4 solutions in LP‐TEM is provided, showing good agreement with simulated mole fractions. [ 28,32,37–46 ]…”

“…Moreover, an overview of reports describing evolution of gold nanostructures from pristine HAuCl 4 solutions in LP-TEM is provided, showing good agreement with simulated mole fractions. [28,32,[37][38][39][40][41][42][43][44][45][46] In this work, the dose rate is calculated for an electron energy of 300 keV and for a liquid film with a constant thickness of about 100 nm to describe our experiments performed in graphene-supported microwell liquid cells (GSMLCs) [47,69] and other graphene-based liquid cell architectures. Naturally, this cannot be matched perfectly with the broad range of experiments reported in literature.…”

“…Besides electron-beam induced heating, [18,19] radiolysis is a crucial factor during LP-TEM, [20][21][22][23] even when radical scavengers are utilized [24,25] or radiolytic shielding via graphene membranes is employed. [26,27] Moreover, radiation chemistry has been identified as a prime driving force to study both reductive formation, [28][29][30] and oxidative etching [31][32][33][34][35] of metallic nanostructures. Operating between the poles of mitigation and utilization of radiation effects is not limited to LP-TEM but is relevant for several techniques using ionizing radiation to investigate structures or processes in liquids in situ or operando such as X-rays.…”

“…However, most LP-TEM studies solely rely on an incomplete description of the chemical environment, ignoring the intra-and interplay of complete clusters of chemical species. For example, investigations of gold nanoparticle evolution in aqueous tetrachloroauric acid (HAuCl 4 ) solution, one of the most frequently used model systems in LP-TEM, [12,28,32,[37][38][39][40][41][42][43][44][45][46] mainly rely on radiation chemistry of pure (and partially even deaerated) water. [21] More accurate descriptions are sparse and only describe gold precursor reduction [24,38] or the radical chemistry of aqueous chloride solutions.…”

In Situ Direct Monitoring of the Morphological Transformation of Single Au Nanostars Induced by Iodide through Dual-Laser Dark-Field Microscopy: Unexpected Mechanism and Sensing Applications

“…Real-time imaging of single nanoparticles during their reactions and motions is vital to understanding their chemical [ 1 , 2 , 3 , 4 ], physical [ 5 , 6 ], and biological properties [ 7 , 8 ]. Although techniques such as atomic force microscopy (AFM) [ 9 , 10 , 11 ], liquid cell transmission electron microscopy (TEM) [ 12 , 13 , 14 ], and scanning electron microscopy (SEM) [ 15 , 16 ] are useful for monitoring single nanoparticles, they are expensive, exhibit low temporal resolution, and typically cannot be conducted under biophysical conditions.…”