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 gamma-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 {111} plane of the core. This can be rationalized by {111}-specific coalescence and Brownian rotation of the impinged nanoparticles despite the shell. (c) 2007 Elsevier B.V. All rights reserved.