Chemical vapour deposition of metal oxides and phosphides
This thesis investigates the deposition of thin films of main group metal phosphide and main group metal oxide compounds on glass substrates by the use of dual source atmospheric pressure chemical vapour deposition. Binary phosphide systems with tin, germanium, silicon, antimony, copper or boron have been examined. Binary oxide systems of gallium, antimony, tin or niobium have also been investigated. Additionally these systems were deposited on gas sensor substrates and evaluated as metal oxide semiconductor gas sensors. Halides were used as the metal precursor, RXPH3.X (R = Cychex or Phenyl) were used as phosphorous precursors and either methanol or ethyl acetate were used as oxygen precursors. These coatings showed good uniformity and coverage and the films were adherent passing the Scotch tape test. The tin phosphide films were opaque in appearance with some signs of birefringence due to differential thickness effects. Germanium phosphide and the gallium, antimony, niobium and tin oxide systems were all transparent, once again birefringence was observed. The films produced from the antimony phosphide and silicon phosphide systems were opaque, grey and metallic. Additional work was conducted on the deposition on a variety of alkali metal and alkaline earth metal fluorides on glass substrates using aerosol assisted chemical vapour deposition. In all cases the films were very powdery and were easily wiped off of the substrate. A number of depositions were carried out combining the aerosol and atmospheric pressure methodologies. A tin oxide film was produced from the atmospheric pressure chemical vapour deposition reaction of tin tetrachloride and ethyl acetate. The film contained tungsten, which was introduced into the reaction using a polyoxometalate delivered via aerosol assisted chemical vapour deposition. Films were analysed using Raman microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive analysis of X-rays, electron probe microanalysis, X-ray photoelectron spectroscopy and ultra violet and visible spectroscopy.