Polypyrrole thin films have been deposited onto a glass substrate by the Langmuir-Blodgett technique to fabricate a selective ammonia (NH3) gas sensor. The d.c. electrical resistance of the sensing elements is found to exhibit a specific increase upon exposure to different gases such as NH3, CO, CH4, H2 in N2 and pure O2. The polypyrrole thin-film detector shows a considerable increase of resistance when exposed to NH3 in N2, and negligible response when exposed to comparable concentrations of interfering gases such as CO, CH4, H2 in N2 and pure O2. The calibration curve for NH3 in N2 at room temperature is measured in the concentration range from 0.01 to 1%. The relative change of the electrical resistance is about 10% for the lower detectable limit of 100 ppm of NH3 in N2. The sensitivity of the Langmuir-Blodgett polypyrrole towards ammonia is considerably higher than that of the electrochemical polypyrrole. The fast rise time and the high sensitivity of the detector are reported as a function of number of the polypyrrole layers. Long-term aging tests of the selective NH3 gas sensor are performed. © 1997 Elsevier Science S.A.

cited By 68