Synthesis and characterisation of Titania thin films

Download files
Access & Terms of Use
open access
Copyright: Nakaruk, Auppatham
Altmetric
Abstract
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 μm) were observed; without insulation, only transparent anatase (<50 nm) was observed. An alternative method for TiO2 film fabrication, spin coating on fused quartz substrates, was studied. The films were of a single grain’s thickness since annealing at all temperatures (750°-900°C) gave identical ~400 nm grain size and film thickness. The anatase-rutile phase transformation occurred at 750°-800°C, with first-order kinetics; annealing at 900ºC gave single-phase rutile. Si contamination from the substrates was critical since it suppressed both TiO2 grain growth (hence, constant grain size) and the phase transformation (hence, need for relatively high phase transformation temperature); its presence also was responsible for the formation of lattice defects, which decreased the transmittances and the band gap.
Persistent link to this record
Link to Publisher Version
Link to Open Access Version
Additional Link
Author(s)
Nakaruk, Auppatham
Supervisor(s)
Sorrell, Charles
Creator(s)
Editor(s)
Translator(s)
Curator(s)
Designer(s)
Arranger(s)
Composer(s)
Recordist(s)
Conference Proceedings Editor(s)
Other Contributor(s)
Corporate/Industry Contributor(s)
Publication Year
2010
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
Files
download whole.pdf 3.15 MB Adobe Portable Document Format
Related dataset(s)