The influence of the precursor clusters on the structural and morphological evolution of nanostructured TiO2 under thermal annealing

We have produced nanostructured titanium dioxide thin films by supersonic cluster beam deposition. The as-deposited films have a nanocrystalline or amorphous structure depending on the mass distribution of the precursor clusters. This can be controlled by aerodynamic separation effects typical of supersonic expansions. On thermal annealing at temperatures from 400 to 800 degreesC in ambient atmosphere, amorphous-to-anatase and anatase-to-rutile phase transitions have been observed. The nanostructure and microstructure evolution of the film upon annealing has been characterized by atomic force microscopy and transmission electron microscopy. The influence of the precursor clusters in the evolution of the film nanostructure at high temperatures has been demonstrated. This observation opens up new perspectives for batch fabrication of devices based on cluster-assembled materials.