Origin of Rapid Coalescence and Active Unstable Fluctuation of Au Nanoparticles under TEM Observation: Electron Bombardment Versus Charge Buildup

Nanoparticles (NPs) in contact with each other observed in a transmission electron microscope (TEM) tend to undergo rapid coalescence. Similarly, isolated NPs show unstable fluctuations and changes in orientation due to active vibration and rotation; these behaviors are accompanied by a rapid diffusion of surface atoms and are likely related to the rapid coalescence of NPs, which has been widely attributed to bombardment by highenergy electrons. However, indirect experimental results have suggested that these phenomena are due to the built-up charge. Here, we used TEM to examine the behavior of gold NPs between insulating and conducting membranes to discern between electron bombardment and built-up charge effects. Our observations indicated that the rapid coalescence and active motion of NPs originate mainly from the built-up charge. This novel finding of charge-enhanced atomic diffusion in NPs helps clarify the mechanisms of many phenomena, such as the almost liquid-like rapid coalescence of NPs that produces smooth, single-crystalline nanowires. In contrast, NPs of the same size may show very sluggish coalescence, producing pearl-like chains, which may be attributed to the absence of charge.

Automated summary

The rapid coalescence and active motion of nanoparticles (NPs) are primarily caused by the built-up charge. This finding helps to clarify the mechanisms of various NP phenomena.