Influence of the structure and morphology on the sensitivity to nitrogen oxides of phthalocyanine thin-film resistivity sensors

Thin-film Zn-phthalocyanine (ZnPc) sensors for the analysis of traces of NO2 in air are prepared using a vacuum evaporation technique, starting from an Eastman Kodak material that has been purified by entrainer sublimation in inert gas. Sheets of Al2O3 are used throughout as substrates. An appreciable sensitivity to NO2 in the 1 – 100 ppm range is observed systematically, but remarkable differences in sensitivity are found in samples apparently prepared in a similar manner. The results show that the sensitivity depends primarily on the structure and morphology of the active layer. Films consisting primarily of β-Pc with a surface rich in elongated whiskers appear to present the largest sensitivity