ASPECTS OF THE CHEMISTRY OF METAL OXIDE SEMICONDUCTOR GAS SENSORS (SEMICONDUCTOR)

Available from UMI in association with The British Library.; The three n-type metal oxide semiconductors SnO{dollar}sb2{dollar}, TiO{dollar}sb2{dollar} and WO{dollar}sb3{dollar} were studied in order to establish their potential as chemical sensing agents. These oxides were mixed with noble metals (Pd and Pt) from Group VIII of the Periodic Table. The low molecular weight reducing gases H{dollar}sb2{dollar}, CO and CH{dollar}sb4{dollar} were used as test gases in air atmospheres.; The semiconductor oxide/noble metal materials were prepared in a variety of phase distributions using methods commonly employed in the production of highly dispersed catalysts.; Chemical and physical techniques were used to characterise the materials and study their chemistry and the redox properties of the bulk materials were investigated using hydrogen-containing atmospheres. The materials were exposed to both oxidizing and reducing atmospheres in X-ray photoelectron spectroscopy and X-ray diffraction experiments in order to study their surface properties and their structural compositions, respectively. The materials were further studied by transmission electron microscopy and also by chemisorption methods using both hydrogen and carbon monoxide as gaseous adsorbates.; Conductance experiments were performed on all the materials in both isothermal and temperature-programmed modes. The results of these experiments were used to establish the sensing properties of the materials and to investigate their kinetic and thermodynamic properties in air and reducing atmospheres. It was found that the materials often had similar types of responses to different gases and relied on similar chemical mechanisms. However, a number of anomalous reactions were observed, particularly with the WO{dollar}sb3{dollar}-based materials.; A sample composed of TiO{dollar}sb2{dollar} and Pt was identified as having properties making it suitable to use as the chemical agent in a miniaturised gas detector. A small device was constructed and its response to various chemical species tested. This sensor showed desirable sensor properties including good reproducibility, sensitivity and short response times.