Disentangling the Effects of Temperature and Dose Rate on Nanoparticle Formation during Liquid-Phase Electron Microscopy

<jats:p>The solution phase synthesis of metal nanocrystals proceeds via physicochemical processes that have yet to be fully elucidated. Variable temperature liquid phase transmission electron microscopy (VT-LPTEM) has emerged as an important technique to enhance our knowledge of nanoparticle formation mechanisms. However, there exist several entangled temperature-dependent phenomena during VT-LPTEM that can influence nanoparticle formation dynamics, including radiolysis, reaction kinetics, and diffusion. Here we show that dose rate and temperature induced increases in gold nanoparticle formation rate are consistent with electron beam induced substrate charging and temperature-dependent diffusion. Formation of thiol stabilized gold nanoparticles was imaged in real time using dose-controlled VP-LPTEM between room temperature and 60 °C. Spherical ~2 nm primary gold nanoparticles formed and attached to the silicon nitride membrane to form secondary aggregates, with nanoparticle attachment rates increasing as a function of temperature and electron dose rate. Interestingly, radiolysis simulations showed that the gold monomer concentration was constant as a function of temperature and dose rate. Instead, we show that dose rate dependent nanoparticle attachment is consistent with electron beam induced charging of the silicon nitride, which increases nanoparticle capture probability and surface concentration of precursor gold anions. The observed temperature dependence is consistent with increased gold nanoparticle diffusion coefficient at elevated temperatures, which permits more rapid transport to the silicon nitride surface. This work establishes a foundation for disentangling dose rate and temperature dependent phenomena during VT-LPTEM imaging and quantification of nanoparticle formation kinetics.</jats:p>