FAST NO2 DETECTION AT ROOM-TEMPERATURE WITH OPTIMIZED LEAD PHTHALOCYANINE THIN-FILM STRUCTURES

As-deposited lead phthalocyanine films prepared by vacuum sublimation are found to consist of fine particles with a mean diameter below 0.2 μm; disordered phases exist between the particles. The response and recovery times of the resistance changes, induced by step changes from clean air to air containing low concentrations of NO2, are very slow for the as-deposited films. By annealing at 300 °C or more, these characteristics can be improved. After an optimized preparation procedure, films with response times of less than 20 s and recovery times of the order of some minutes, even at room temperature, are observed. They exhibit fine crystals with a mean diameter of the order of 0.2 μm and the presence of a disordered phase is not confirmed. The lack of reproducibility and a fast recovery time observed in the behaviour of these films are attributed to the presence of larger crystals in the conductive path. © 1990.