Synthesis and characterisation of Titania thin films

The thesis presents publications reporting TiO2 thin film fabrication by spray pyrolysis. A conceptual model of spray pyrolysis mechanism was developed and validated as a diagnostic tool to explain the deposition process, which shows that CVD can be achieved by this method.Effect of deposition temperature: TiO2 films were coated on glass using ultrasonic spray pyrolysis for 1 h at 300°-400°C. At 300°C, the films were amorphous; higher temperatures gave films of anatase. With increasing film thickness, the optical transmission decreased. The indirect optical band gap decreased with increasing deposition temperature, dropping from 3.47 eV to 3.23 eV. Effect of deposition time: TiO2 films were deposited on glass using ultrasonic spray pyrolysis at 400°C over 30-120 min. The thin films (420-1290 nm thickness) showed increasing thickness and roughness but decreasing transmittance with increasing deposition time. In the absence of published kinetics data for the deposition of such films, the first-order growth rate was found to be 11 nm/min. Effect of annealing temperature: TiO2 films were prepared by ultrasonic spray pyrolysis on fused quartz at 400°C and/or annealed in air at 600°-1000°C. The films deposited 400°C (50 nm grains) and annealed at 600°C (100 nm grains) showed single-phase anatase of high visible-light transparency. Films annealed at 800°C and 1000°C showed mixed-phase anatase + rutile and pure rutile, respectively. Laser Raman microspectroscopy and X-ray diffraction showed the presence of residual stress, probably resulting from contamination, Si diffusion into the films, and/or oxygen deficiency.Effect of thermal gradient: TiO2 films with mixed-phase rutile + anatase and anatase only were deposited on fused quartz by ultrasonic spray pyrolysis at 400°C. The presence and absence of insulation around the entrainment pathway above the substrate/hot plate was studied. The films were assessed in terms of mineralogy, microstructure, and visible-light transmission. With insulation, opaque mixed anatase (~30 vol%; <50 nm) + rutile (~70 vol%; ~1 &#956;m) were observed; without insulation, only transparent anatase (