XPS Investigations on Conducting Polymers


Abstract: X-ray photoelectron spectroscopy, XPS, was used for the characterization of electrically conducting polymeric materials. In the spectrum of polypyrrole, PPy, the Nls region exhibits two peaks, at 402.0 and 399.8 eV, corresponding to -N$^+$- and -N- moieties, respectively. The intensity of the N$^+$ peak decreases as the material loses its conductivity, hence the ratio of the experimentally derived N$^+$/C atomic ratio correlates exponentially with the measured conductivity. A similar observation also exists between the F$^-$/C atomic ratio both in polypyrrole and polythiophene. In the XPS spectrum of the composite material prepared using polyaniline, PAN and polyvinylchloride, PVC, two different kinds of Cl2p spin-orbit doublets are present after irradiation by ${\ }^{60}$Co $\gamma$-rays. One of the Cl2p doublets can be assigned to the C-Cl in PVC and the other one is assigned to Cl$^-$ ions appearing after radiation. Since no Cl$^-$ peak is observed in PVC even after radiation, the presence in the composite must be related to dehydrochlorination of PVC and subsequent capture of the H-Cl by the neighboring PAN moieties. The measured Auger parameter of the Nals level of NaBr deposited on an oxidized form of the conducting polymer is between the values of NaBr deposited on Au (metal) and on Si (semiconductor). However, when NaBr is deposited on a reduced form of conducting polymer, the corresponding value approaches to that deposited on quartz (insulator).


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