| The objective of this thesis was to use a novel process to fabricate and characterise semiconducting metal oxide sensors which detect NOx . This process involves the photochemical deposition of thin solid films of amorphous precursor complexes. The precursor film is exposed to light and photochemically produces the desired material, in this case the sensing element.; The metal complexes, M(CO)5PPh3 and M(CO) 4(LL)5 (M = Cr, Mo, W; LL = H(CH3)NCH2CH 2NH(CH3), H2NCH2CH2N(C 2H5)2 (Et2-en), H2NCH2CH2NH 2) were synthesised. Upon spin coating, these complexes all form photosensitive amorphous films. The film quality depends on both the metal centre and the ligands. The best starting materials were found to be M(CO)4(Et 2-en) (M = Cr, Mo, W). Auger analysis indicates the formation of contamination free Cr0.65O, Mo0.27O, and W0.5O from these precursors.; The solid state photochemistry of the above metal complexes is described. The complexes containing the nitrogen donor ligands were found to follow a one photon process. The PPh3 complexes were found to decompose via a two photon process. The quantum yields were determined with a kinetic equation derived for a one or a sequential two photon process. The photoefficiency was found to depend on the metal centre as well as the ligand environment.; Finally, we will conclude by presenting the characteristics of tungsten and molybdenum tungsten oxide sensors at various operating temperatures. The electron transport mechanisms for semiconducting metal oxides are reported. The electron flow in amorphous tungsten oxide devices was found to follow the variable range hopping conduction whereas the electron conduction in amorphous molybdenum doped tungsten oxides was via the single electron hopping mechanism. These sensors were found to respond to sub-ppm NOx at 100°C. The reproducibility, specificity and stability of these devices promise a reliable NOx sensor operation for environmental monitoring. |
