The Surface Species of Poly(p-Phenylene Vinylene) and Their Effects on Calcium Interface Formation

X-ray photoemission spectroscopy (XPS) was used to investigate the cespecies of poly(phenylene vinylene) (PPV). PPV samples with 1% S and 5-10% O impurities were obtained whenever the corresponding sulfonium precursor polymers were subjected to XPS scans prior to thermal conversion. Relatively “clean” PPV surfaces with 4-5% oxygen atoms as the only detectable impurities were obtained by performing the thermal conversion in an argon circulating oven or in ultra high vacuum at 320°C, without prior XPS scan. Therefore the S impurities were resulted from x-ray induced chemical reactions which might involve the formation of sulfur ylides. By resolving the O 1s peak, four types of oxygen species were identified, namely carbonyl (C =O), hydroxy (C-OH), ether (C-O-C) and the carboxylic groups (HO-C=O). The oxygen groups reacted With Ca to form CaO. A reversed surface band bending was found for the S containing PPVs with respect to that for the S free PPVs during the Ca interface formation. Our overall results suggest that the barrier height at metal/PPV interface is highly sensitive to the surface preparation and relatively insensitive to the work function of the metals.