In situ atomic-scale TEM observation of Ag nanoparticle-mediated coalescence in liquids

Silver nanoparticles can be applied in many fields due to their various properties, such as their morphology and size, and have been explored widely in many studies. Specific geometric shapes can be synthesized via non-classical particle-mediated growth by controlling the synthesis parameters. However, the mechanism and evidence of silver nanoparticle growth have been indirectly studied, and the microscopic internal evolution of coalescence via particle-mediated growth has not been well studied. In this work, we observed the coalescence process at the atomic level using liquid in situ transmission electron microscopy. A complete overview of the main mechanism of coalescence was provided. In addition, the relaxation reaction that prompts coalescence to reduce the overall energy was systematically studied. For instance, the dislocations, grain boundaries, and stacking faults, even the defect-free nanoparticle, were reshaped by mass transport via surface, grain boundary, and twin boundary migration. The nanocrystal tends to form a thermodynamic stabile structure by atomic migration. The validation of the coalescence process at the atomic scale sheds light on the synthesis of nanostructured materials with non-classical particle-mediated growth.