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Germanium powder was thermally evaporated under a vacuum onto unheated substrates as well as substrates heated to 200 °C. The striking feature was that the resulting films were transparent. Chemical analysis using x-ray photoelectron spectroscopy depth profiling indicated that oxygen was present throughout the thickness of the films, and therefore the films were composed of substoichiometric germanium oxide. The source of oxygen was investigated, and traced to the source material. Subsequently, the optical constants and the band gaps of the films were determined from spectrophotometric measurements. These properties were found to be intermediate between those of pure germanium and germanium dioxide, with values appropriate for optical applications in the visible range. [ABSTRACT FROM AUTHOR]

Mixed films of cerium oxide (CeO2) and tungsten oxide (WO3) were deposited on unheated substrates by co-evaporation. The films were annealed in air at 500°C for 2 h. The surface morphology of the films was characterised using atomic force microscopy. The chemical composition was determined using X-ray photoelectron spectroscopy. The optical properties were derived from normal incidence reflectance and transmittance measurements. The films were investigated for the detection of carbon monoxide. The effects of the operating temperature and gas concentration on the performance of the sensor were investigated. The sensor response and recovery times were also measured. [ABSTRACT FROM AUTHOR]

Thin films of molybdenum oxide were deposited in vacuum by pulsed laser ablation using a xenon fluoride (351 nm) and a krypton fluoride (248 nm) excimer lasers. The films were deposited on unheated substrates and were post-annealed in air in the temperature range 300–500°C. The structural, morphological, chemical, and optical properties of the films were studied. As-deposited films were found to be dark. The transparency of the films was improved with annealing in air. The films were polycrystalline with diffraction peaks that belong to the orthorhombic phase of MoO3. The surface morphology of the films showed a layered structure. Both the grain size and surface roughness increased with annealing temperature. The stoichiometry of the films improved upon annealing in air, with the best stoichiometry of MoO2.95 obtained for films deposited by the XeF laser and annealed at 400°C. Similarly, the best transparency, with a transmittance exceeding 80%, was obtained with the films annealed in the temperature range 400–450°C. [ABSTRACT FROM AUTHOR]

The existing methods for determining the optical constants of inhomogeneous thin films deal with non-absorbing films or at the most with films that have very small absorption (k < 0.02). In this work, a method is presented for the determination of the optical constants of inhomogeneous thin films with large optical inhomogeneities. The optical constants are derived from normal-incidence measurements of reflectance and transmittance. The refractive index was modelled by quadratic variation. However, the absorption index was replaced by its mean value. The accuracy of this assumption was tested and its range of validity was determined. Subsequently, the method was applied to the determination of the optical constants of cerium oxide thin films. [ABSTRACT FROM AUTHOR]

Thin films of tin oxide were deposited by electron beam evaporation. The effects of the electrode materials (Ag, Al, Au and Pt) and different electrode configurations on the CO-sensing of tin oxide thin films were investigated. The Pt and Au electrodes with bottom electrode configuration show much higher response than Ag and Al electrodes. The sensor response and recovery times have also been measured. The films were characterized using X-ray diffraction and X-ray photoelectron spectroscopy. All the films were found to be amorphous. It was found that the CO-sensing properties depend both on the electrode materials and configuration.

Undoped thin films of tin oxide and those doped with indium oxide and nickel oxides were deposited by electron beam evaporation. The effects of the film thickness and preparation conditions (films prepared with or without the presence of oxygen environment during deposition) on the optical and carbon monoxide sensing properties of the films were studied. The films were characterized using X-ray diffraction and X-ray photoelectron spectroscopy and optical spectroscopy techniques. All the films were found to be amorphous. It was found that the sensitivity of the films to CO increased with the thickness and the porosity of the films. It was found that their selectivity to CO gas relative to CO(2) and SO(2) gases could be improved upon doping the films with indium (or nickel) oxide.