MOSSBAUER AND MICROSTRUCTURAL STUDIES OF IRON PHTHALOCYANINE AS A POTENTIAL GAS SENSOR

Phthalocyanines have been noted for their use as chemical sensors. Iro n phthalocyanine (FePc) can be used as a model to study the gas sensin g mechanism using transmission Mossbauer spectroscopy to characterize bulk properties, and conversion electron Mossbauer spectroscopy (CEMS) to study surface interactions. One major aim of the work is to monito r an FePc sample before, during and after exposure to various gases. P roblems have been encountered collecting CEMS spectra from FePc films and crystals. A crystal morphology study has been undertaken in an att empt to explain this difficulty. FePc exists in at least two phases; t he alpha- and beta-phases. Purification of crude FePc by entrainer sub limation yields beta-crystals. Vacuum sublimation of beta-crystals ont o substrates gives alpha-FePc films which, when annealed, become beta- FePc films. Scanning electron microscopy shows that the as-deposited f ilm consists of fine crystallites (0.1 mum diameter). Transmission Mos sbauer spectroscopy of beta-FePc gives an expected doublet, whilst the alpha-FePc shows very little absorbance, indicating a low or zero rec oil free fraction (f) at room temperature. The significant reduction i n f may be a result of the morphological change resulting in small cry stallites. Variable temperature transmission Mossbauer spectroscopy of the beta-phase yields a Debye temperature of 189 K and f = 0.33 at 29 1 K. Current work is under way making a similar study of the alpha-pha se and work is planned to evaluate whether the gas sensing properties of alpha-FePc are similar to beta-FePc.