Condensation, crystallization and coalescence of amorphous Al2O3 nanoparticles

The amorphous aluminum oxide (Al2O3) nanocondensates produced by energetic pulse laser ablation on Al target under oxygen background gas, for a very rapid heating/cooling effect, have been observed by transmission electron microscopy (TEM). They were found to transform into γ-Al2O3 core and amorphous shell in tensile state at a critical diameter of about 20 nm upon electron irradiation. The partially crystallized nanoparticles were unified or twinned over the {1 1 1} plane of the core. This can be rationalized by {1 1 1}-specific coalescence and Brownian rotation of the impinged nanoparticles despite the shell.