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 synth esized polypyrrole film in its salt and partially undoped/deprotonated form s. Changes in the N(1s), S(2p) and Al(2p) core-level signals, as well as ch anges in surface elemental stoichiometries, were carefully monitored. It wa s 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 th e polymer to that generally observed in the completely undoped or 25% depro tonated 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 inc rease in oxygen concentration at the metal/polymer interface. The formation of the N-pi-AlOz complex disrupted the pi-electron conjugation in the imin e units and reduced the imine site to a state equivalent to that of the ami ne structure, causing the observed decrease in the intrinsic oxidation stat e of the polymer. (C) 1999 Elsevier Science S.A. All rights reserved.