Atom-probe study of a conducting polymer: The oxidation of polypyrrole

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Abstract
Oxidation of the ClO− 4 and BF− 4doped conducting polypyrrole (PP+ClO− 4 and PP+BF− 4) was studied using the high mass resolution atom probe. The specimens were prepared by depositing a PP film on a Pt tip electrochemically. At the early stage of oxidation, O− 2 ions diffused into the PP film and reacted with C atoms of the PP film. As oxidation proceeds, hydrogen of the PP film forms hydro‐oxides and diffuses out of the PP film. The carbon–oxygen bonds also transform to the stable double bonds, C=O. Thus the fragment ions detected from the fully oxidized PP film were CO+, CNO+, C2O+ 2, C2N2O+ 2, C2O2+ 2, C2N2O2+ 2, and C3N2O2+ 3, indicating that nearly all N atoms were strongly interacting with C and O atoms. Oxidation progresses from the surface and the thickness of the fully oxidized section is approximately 66 nm in the specimen exposed to air for three months. The boundary between the oxidizedsurface layer and the unoxidized substrate PP section was found to be rather abrupt. The mass spectra of the PP+ClO− 4 and PP+BF− 4films are identical but the oxidation of the PP+BF− 4 advances remarkably faster than that of the PP+ClO− 4film. No satisfactory explanation is available at present. No doped elements were detected except for B atoms. Tentative explanations are given.