In this work, it is shown that thiol-protected Au nanoparticles (AuNPs@SR) of approximately 3.4 nm size suffered unexpectedly high radiation damage under standard transmission electron microscopy (TEM) operating conditions. For metallic systems (conducting sample), it is expected that the greatest contribution to the damage comes from knock-on displacement, but radiolysis is the most probable radiation damage mechanism for organic samples. The radiation damage of the electron beam produces huge changes in AuNPs' structure, leading to coalescence of the Au cores when their {100} surfaces are facing each other. The complete coalescence process involve thiol desoprtion, AuNPs' reorientation, and surface diffusion of Au adatoms, which produce the oriented attachment of the Au cores. The knock-on displacement cannot explain by itself the time taken by the entire process. Through a rigorous analysis, we rationalize the results considering that because of the small size of AuNPs they have a lower electron density than the bulk material which favors radiolytic damage.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
