Study of ammonia-gas-induced irreversibility in polypyrrole films

Polypyrrole’s conductivity as a function of polymerization temperature and its properties on treatment with ammonia gas are studied. Electronic structures of PF6 (hexafluorophosphate) doped polypyrrole (PPY) films grown at −40, 0, and 20 °C, before and after ammonia treatment, are compared using angle resolved photoemission spectroscopy, electron paramagnetic spectroscopy, and semiempirical calculations. The valence band electronic structures of these polypyrrole films largely depend on polymerization temperature, and ammonia treatment. The light-polarization-dependent valence band structures reflect ordering of polymer chains with decreasing polymerization temperature. The irreversibility properties of polypyrrole, which can be used as an ammonia gas senor, are shown to possibly arise from detachment of the dopant molecules under pumping.