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

摘要

The role played by the laser fluence on the Al2O3 target when depositing VOx: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 VOx 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. © 2007 Elsevier B.V. All rights reserved.