In situ XPS study of thermally deposited aluminium on chemically synthesized polypyrrole films

X-ray photoelectron spectroscopy was employed for the in situ study of the interactions between thermally deposited aluminium and the chemically synthesized polypyrrole film in its salt and partially undoped/deprotonated forms. Changes in the N(1s), S(2p) and Al(2p) core-level signals, as well as changes in surface elemental stoichiometries, were carefully monitored. It was found that the incoming aluminium atoms reacted initially with the dopant molecules of the film to form a salt. The undoping process was accompanied by an increase in the intrinsic oxidation state ([N–]/[–NH–] ratio) of the polymer to that generally observed in the completely undoped or 25% deprotonated polymer. The intrinsic oxidation state, however, started to fall at high aluminium loading. Furthermore, the migration of bulk adsorbed oxygen to the surface in response to the Al deposition process resulted in an increase in oxygen concentration at the metal/polymer interface. The formation of the N-π-AlOz complex disrupted the π-electron conjugation in the imine units and reduced the imine site to a state equivalent to that of the amine structure, causing the observed decrease in the intrinsic oxidation state of the polymer.