Ta₂O₅ thin films have been prepared by evaporation from a tantalum oxide precursor and by assisting the growth of the films by oxygen and nitrogen ion bombardment (IBAD). The obtained thin films depict different microstructures and optical and dielectric properties. In general, the films prepared by evaporation have lower refraction indices that those prepared by IBAD. In this case a clear correlation exists between the ion current and energy and the properties of the films. The trend of dielectric properties of these thin films agrees with that defined by their optical properties. They also agree with the microstructrue of the films as determined by SEM. A particular type of films was found when prepared by evaporation under grazing conditions. These films depict a columnar microstructure with oblique columns and an extremely high porosity. Refraction indices ranging from 1.7 to 1.2 have been obtained for these thin films.

Another interesting property of these thin films refers to its wetting behaviour under UV light. In literature there are many papers dealing with the conversion of the TiO₂ surface from partially hydrophobic into fully hydrophilic by UV irradiation. In this work we also show that Ta₂O₅ thin films present a similar behaviour changing from hydrophobic into hydrophilic by illumination. A careful study of this type of transformation is being carried out as a function of the microstructural and structural properties of the films. Doping of Ta₂O₅ thin films with foreign cations and with nitrogen has revealed to be an effective way to induce a partial change in wetting angle by using visible light for the illumination.

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