Chemiresistor-type NO gas sensor based on nickel phthalocyanine thin films

The sensing characteristics of nickel phthalocyanine (NiPc) thin films for use in a chemiresistor-type nitric oxide gas sensor are discussed. The gas- sensing properties, including current transient, sensitivity, response time , and aging, are studied. A kinetic model proposed in the literature for se nsing NO2 with lead phthalocyanine (PbPc) thin films, in which adsorption i nvolves displacement of surface adsorbed O-2 from a range of heterogeneous sites, can be used to explain our experimental results. It is inferred that exposure to NO concentrations lower than 50 ppm only involves the populati on of weak adsorption sites, while exposure to NO concentrations higher tha n 50 ppm may involve the population of stronger adsorption sites. Repeated step changes in NO concentrations of 50 ppm could result in a significant c hange in response currents within the first five cycles, presumably due to the presence of an irreversible adsorption. Further analysis of current res ponses reveals that the lower the concentration of NO, the larger the sensi tivity. For a lower concentration range, between 5 and 50 ppm NO, the sensi tivity ties between 0.41 and 0.42, while for a higher concentration range, between 50 and 500 ppm, the sensitivity decreases to about 0.17 to 0.19. (C ) 2001 Elsevier Science B.V. All rights reserved.