The role of the laser fluence on the Al2O3 target in the nanostructure and morphology of VOx: Al2O3 thin films prepared by pulsed laser deposition

The role played by the laser fluence on the Al₂O₃ target when depositing VO_x:Al₂O₃ nanocomposite thin films by alternate ablation from ceramic alumina (Al₂O₃) and metallic vanadium (V) targets in vacuum has been studied. The fluence and number of pulses on the V target to prepare the nanoparticles has been maintained constant, while the fluence used to grow the Al₂O₃ host has been varied from 1.3 to 3.9 J cm^-2. The optical properties of the films, namely in-situ reflectivity during growth and extinction coefficient, evidence that the properties of the nanoparticles change as a function of the laser fluence on the Al₂O₃ host. Transmission electron microscopy analysis shows the formation of vanadium oxide nanoparticles with average diameters in the range of 4.6 nm. Structural analysis of the nanoparticles shows that they are mainly crystalline. Phases of VO_x with average [O]/[V] ratios from 1.7 to 2.2 have been identified with the most commonly observed being V₃O₅. This is in agreement with low heat of formation of this oxide. It is shown that the oxidation of the nanoparticles induced during the deposition of Al₂O₃ is very efficient since no metallic V nanoparticles are formed even for the lowest fluence used.