Table of Contents

Abstract: A first step towards a microfabricated potentiometric thin-film sensor array for the simultaneous detection of Pb²⁺, Cd²⁺ and Cu²⁺ has been realized. The sensitive layers used are on the basis of chalcogenide glass materials. These thin-film chalcogenide glass materials that consist of mixtures of Pb-Ag-As-I-S, Cd-Ag-As-I-S or Cu-Ag-As-Se have been prepared by pulsed laser deposition technique. The developed sensor array has been physically characterized by means of scanning electron microscopy and Rutherford backscattering spectrometry. The electrochemical sensor characterization has been performend by potentiometric measurements.

Abstract: In this paper the characteristics of a CuO-BaTiO₃ based CO₂ gas sensor was investigated. The sensitivity of the CuO-BaTiO₃ based CO₂ sensor was influenced by doping various metal elements such as Au, Ag, Pt, Pd, Ce, Mg, Sr, La, Zn, Fe and Bi, which were added as a pure metal or in the form of metal oxides. It was found that Ag is the most suitable additive among all substances tested. The Ag-doped CO₂ gas sensor has better sensitivity and lower operating temperature, with a detection concentration range of from 100 ppm to 10%. The sensor also shows good stability.

Abstract: Benzene is a carcinogen with a maximum permitted exposure limit in the atmosphere of 16.25μg m^-3 (5 ppb). There is a need for an inexpensive instrument for measuring benzene concentrations, particularly in urban areas. We have shown that thin films of titanium dioxide dispersed in poly(vinylidenfluoride) are sensitive to benzene at room temperature with possible applications in benzene monitors. In this paper, we present a detailed study into the direct current electrical characteristics of the films when exposed to benzene. The current I through the films increase linearly with applied voltage, V, at low applied voltages (V ≲0.6V) and at higher voltages, I α V⁵. The results are consistent with the films being p-type semiconductors and, at higher voltages, the conduction is dominated by a space charge limited process caused by negative traps with an average energy of 0.1 eV. The films are sensitive to benzene only at the higher voltages. The proposed mechanism is that benzene molecules on the surface of the films reduce the concentration of holes. The relative resistance of the films increases linearly (r = 0.92) with benzene concentrations (sensitivity of 0.042% ppm^-1) and a detection limit of 10 ppm. The films have response times to increasing and decreasing concentrations of benzene of about 1 and 5 min respectively.