Nanocrystalline TiO₂ films studied by optical, XRD and FTIR spectroscopy

We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temperatures between 200 and 350 °C by a technique of ultraviolet-assisted injection liquid source chemical vapor deposition (UVILS-CVD) with 222 nm radiation. The composition and optical properties of the films deposited have been studied using a variety of standard characterisation methods. A strong absorption peak around 438 cm^-1, corresponding to Ti-O stretching vibration, was observed by Fourier transform infrared spectroscopy for different deposition temperatures. Nanostructured films on Si wafers were observed by atomic force microscopy while X-ray diffraction results showed that crystalline TiO₂ layers could be formed at deposition temperatures as low as 210 °C. The deposition kinetics and influence of the substrate temperature on the film are discussed. The activation energy for this photo-CVD process at temperatures between 200 and 350 °C was found to be 0.435 eV. This is much lower than the value (E_a = 5.64 eV) obtained by conventional thermal CVD. The thicknesses of the films grown, from several nanometers to micrometers can be accurately controlled by changing the number of drops introduced by the injection liquid source. Under optimum deposition conditions, refractive index values as high as 2.5 and optical transmittance of between 85% and 90% in the visible region of the spectrum can be obtained.