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 sensing NO2 with lead phthalocyanine (PbPc) thin films, in which adsorption involves displacement of surface adsorbed O2 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 population of weak adsorption sites, while exposure to NO concentrations higher than 50 ppm may involve the population of stronger adsorption sites. Repeated step changes in NO concentrations of 50 ppm could result in a significant change in response currents within the first five cycles, presumably due to the presence of an irreversible adsorption. Further analysis of current responses reveals that the lower the concentration of NO, the larger the sensitivity. For a lower concentration range, between 5 and 50 ppm NO, the sensitivity lies 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.