The role of oxygen adsorption on phthalocyanine thin film NH3 sensors is studied. Observations of the effect of NH3 and NH3/air mixtures on the dark conductivity of Pc devices show that both, purity of the Pc and the electrode material used to be of importance. X-ray photoelectron spectroscopy and ion-beam etching studies show that whilst entrainer sublimation increases the film purity markedly, Ag, Pb, Na, and Cl impurities remain in the films and may affect the electrical behaviour. Whilst there is some evidence that bulk oxygen absorption affects device conductivity, XPS results indicate that for Pc films previously exposed to air, oxygen is primarily adsorbed on the surface in the form of water vapour. NH3 sensitivity arises due to a catalytic reaction with the donor NH3, removing oxygen from the surface and decreasing the film conductivity.
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Wilson et al. (1986) studied this question.
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