Calcium induced oxidation of PPV studied with X-ray photoelectron spectroscopy and secondary ion mass spectrometry

We have investigated the interaction of oxygen with the polyphenylenevinylene (PPV)/calcium interface by means of X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The interface was prepared by thermal evaporation of several Angstroms of calcium on a spincoated OC1C10-PPV layer. We found an increase of the number of oxygen atoms bound to the carbon of the polymer if the PPV/calcium interface was exposed to oxygen, which shows that the oxidation of the PPV was promoted by the presence of calcium. In the carbon Is spectra a structure developed which may be interpreted as strongly oxidized carbon or the formation of a calcium-oxygen-polymer complex. Previously we showed that devices fabricated with OC1C10-PPV as electroluminescent polymer layer totally failed when the polymer layer was exposed to oxygen in the dark after deposition of calcium. The results found with XPS show that the device failure is due to the oxidation of the polymer. SIMS results suggest that the oxidation mechanism of the polymer starts with the formation of a carbide bond between the polymer and the calcium during evaporation which oxidizes during exposure to oxygen. (C) 2002 Elsevier Science B.V. All rights reserved.