Structural and morphological characterization of TiO2 thin films synthesized by spray pyrolysis technique.

Thin films of nanocrystalline TiO2 were synthesized by spray pyrolysis technique in the temperature range 300 degrees C to 550 degrees C in steps of 50 degrees C. The films were coated on glass and quartz substrates by ultrasonic nebulization of titanium-oxy-acetyl acetonate followed by pyrolysis. The structure and morphology of the thin films were characterized by X-ray Diffraction (XRD), Raman Spectroscopy (RS) and Scanning Electron Microscopy (SEM), while the optical band gaps were measured by Spectroscopic Ellipsometry (SE) and UV-Visible spectroscopy. XRD investigations revealed distinct crystal structures of the films synthesized above and below 300 degrees C. While films grown at substrate temperature 300 degrees C were amorphous, those grown at 350 dgrees C and above showed tetragonal anatase crystal structure. The morphological investigations from SEM showed that the films deposited at 350 degrees C were porous and exhibited flower like morphology. The microstructures of the films grown on quartz at 450 degrees C were found to be uniform and dense. The nominal grain sizes evaluated from High Resolution SEM (HRSEM) studies were approximately 20 nm and compared well with the grain sizes calculated from XRD. The band gap values calculated from ellipsometry studies were approximately 3.7 eV and 3.95 eV for the films grown at 450 degrees C and 350 degrees C, respectively. This is in good agreement with those obtained from UV-Visible spectroscopy.