DOPING MECHANISMS OF PHTHALOCYANINES BY OXIDIZING GASES - APPLICATIONTO GAS SENSORS

The present paper proposes a model for the action of the oxidizing gas es O-2 and NO2 on the electrical conductivity of polyfluoro-aluminum-p hthalocyanine thin films. The proposed doping mechanism makes it possi ble to separate the physical process (physisorption, diffusion, displa cement of previously adsorbed species) and the chemical process (chemi sorption or charge transfer). Because of their different kinetics, the se two processes are clearly seen in the transient response of the fil m conductivity which follows a sudden change in the temperature. Sever al experimental results obtained in our laboratory, or quoted in the l iterature, can be explained by our model, especially the power-law dep endence of the conductivity on the gas concentration. Conclusions are drawn about the use of such films as sensitive elements for gas sensor s.