Growth and structure of TiO2 thin films deposited inside borosilicate tubes by spray pyrolysis

Titanium dioxide thin films were deposited inside borosilicate glass tubes by a simple, reproducible spray pyrolysis technique. The tubes had 22 mm of internal diameter and 120 cm of length. Films were transparent, uniform on almost 80% of the tube length, non-light scattering, and well adhered to the substrate. Transmission electron microscopy analysis shows that titanium oxide films are polycrystalline, and their structure corresponds to a mixed phase of anatase and rutile. The microstructure of the films was built by irregular closed-packed grains of around 100–500 nm wide. Cross sections of the films were analyzed by scanning electron microscopy and Z-contrast techniques. This analysis showed that the grains were composed by very small crystallites of about 3–5 nm.