Interactions of evaporated aluminum atoms with polyaniline films — effects of dopant anion and adsorbed oxygen

Aluminum was thermally deposited onto H2SO4-protonated, HClO4-protonated and neutral emeraldine (EM) base films. The interfacial interactions of Al atoms with these EM films were studied in situ by X-ray photoelectron spectroscopy (XPS). The Al atoms interact preferentially with the dopant anions in the cases of the protonated EM films, and with the nitrogen atoms of the conjugated polymer backbone in the case of the neutral EM film. For the H2SO4-protonated EM film, interactions with Al resulted in the formation of aluminum sulfate species, whereas, for the HClO4-protonated film, the reaction resulted in the decomposition of the perchlorate dopant and the formation of aluminum chloride species. For the neutral EM film, the incoming Al resulted in a decrease in the intrinsic oxidation state of the polymer. The migration of bulk-adsorbed oxygen to the surface in response to Al deposition was observed in all of the EM films, and the formation of aluminum oxides, such as Al2O3, suggests that the adsorbed oxygen plays an important role in the interface formation.