Amorphous-to-nanocrystalline transformations kinetics in SbOx films

Amorphous SbOx films with x = 0.37 and x = 0.45, grown by de reactive sputtering, have been annealed in vacuum either recording the optical transmission or following the structural changes in a transmission electron microscope. The results show that the crystallization of the films occurs in two stages, both stages being accompanied by specific changes in the optical properties. The first stage observed is the nanocrystallization of a primary phase antimony, which leads to a material consisting of metal crystals embedded in a network of amorphous material with a composition close to that of the Sb2O3 stoichiometric oxide. The second stage relates to the crystallization of the amorphous material and occurs at higher temperatures. The kinetics of the nanocrystallization process on the micrometre scale and its dependence on the oxygen content of the film are discussed in the framework of the Johnson-Mehl-Avrami (JMA) formulation by measuring the crystal growth rate, the nucleation rate and the dependence of the crystallized fraction on time. The results show that optically monitored nanocrystallization from the amorphous phase can be a suitable means for producing nanocomposite materials from amorphous oxides and that the JMA formulation can be a valid approach for analysing the process.