Nano dance: Unraveling Ceria's self-assembly symphony

Self-assembly mechanism of ca. 2 nm Ce_xO_y (ceria) nanoparticles (NPs) was studied ex-situ and in-situ in liquid environment. We have fabricated, ex-situ using thermal methods, ceria NPs, which self-assembled into 150 nm spherical clusters. To observe the self-assembly process in real time, liquid cell Transmission Electron Microscopy (LC-TEM) was applied to synthesize ceria nanostructures in-situ. The electron beam was used to generate reducing agents and trigger the crystallization of ceria nanoparticles leading to sponge-like vast agglomerates, composed of numerous ceria nanoparticles, having a crystalline structure. The in-situ LC-TEM experiments show that the dose rate is the factor governing the synthesis and dissolution of the nanoparticles, independently if, they were synthesized in-situ or ex-situ. At high electron dose rate the balance is tipped towards synthesis over dissolution, while reducing the dose rate cause the nucleation to be insufficient to sustain NPs growth.