The influence of ammonia, chlorine and nitrogen dioxide on chloro-aluminium phthalocyanine thin films

Amperometric gas sensors were prepared by thermal evaporation of a chloro-aluminium phthalocyanine (ClAlPc) thin film onto inter-digital gold electrodes with 100 μm spacing. The behaviour of these thin films on exposure to NO2, Cl2 and NH3 gases and the suitability of ClAlPc as a material for use in a practical gas sensors was investigated with zero grade air as the reference atmosphere. A change in resistivity of the ClAlPc thin film sensors was observed on exposure to ammonia and chlorine at several different temperatures. In particular, it was found that on increasing the temperature, the sensitivity of the ClAlPc thin film decreases a little, but the reversibility is greatly enhanced. This means that ClAlPc based toxic gas sensors could operate at lower temperatures than their mono-phthalocyanine counterparts. The temperature of maximum sensitivity (Tmax) and the minimum temperature for good reversibility (Tmin) have been determined for ClAlPc sensors ‘doped’ with Cl2 and NO2. It was found that these characteristic temperatures can provide information on the concentration and the nature of the gas to which the sensor is exposed and so could perhaps be used to distinguish between the different adsorbed species. Activation energies for conduction were also measured in the presence of the test gases.