Detection of chlorinated methanes by

Abstract

Tin oxide thin films prepared by thermal oxidation of Sn films were used for the detection of chlorinated methanes (CH₂Cl₂, CHCl₃ and CCl₄). This resulted in better chemical selectivity, sensitivity, response speed and detection limit than seen with previous detectors. The temperature dependence of the sensing of 1% CCl₄ gas was studied and the best sensing behavior was observed at 300 °C. The films showed different chemical selectivity in both speed and direction of sensing response to each gas and were stable for more than 3 weeks under operating conditions. The films showed rapid gas sensing (<40 s to reach 90% of full response) and low detection limits (<4 ppm CCl₄). The role of oxygen in the detection of chlorinated methanes and in resistance changes without chlorinated methanes was also studied. The changes at the surface of the film after gas sensing were examined using scanning electron microscopy with energy-dispersive X-ray spectrometry.