Synthesis and characterization of nanostructured TiO2 and TiO2/W thin films deposited by co-sputtering

Nanostructured TiO2 and TiO2/W thin films were deposited on Corning glass substrates by RF and DC magnetron co-sputtering at room temperature, using three targets of TiO, Ti and W. After deposition, samples were subjected to an annealing treatment in air at 500 degrees C for 3 hrs. The effect of the annealing treatment and tungsten addition to the TiO2 matrix were studied by Raman spectroscopy and X-ray diffraction. Morphology and composition was studied with field emission scanning electron microscopy and optical characterization was made with UV-Vis spectroscopy. All the obtained samples presented an amorphous TiO2 phase; however, after the annealing treatment, a crystallization process from amorphous to anatase phase occurred with gain sizes between 15.6 and 18.3 nm, additionally, a small amount of ruffle was also observable. The SEM images corroborated the XRD behavior, besides it was possible to calculate the thickness of the films which was greater for the W-doped films owing the extra power of the sputtering growth, and after the samples had the thermal treatment the thickness decreased due to a more organized structure. Finally, the UV-vis transmittance analysis revealed that the transmittance is higher in heat-treated films as compared to those without any thermal treatment; also, the TiO2 thin films showed a greater transmittance than the W doped TiO2 films, reaching 91%. The lack of transmittance in the non-thermal-treated films made it impossible to compute the band gap of the films; nevertheless, for the thermal-treated films the band gap had a minimal change to the classic TiO2 bang gap value, even for the W doped sample, providing them with the benefits of the tungsten within the same TiO2 structure due to a great homogenization on the structure.