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 sur face species of poly(phenylene vinylene) (PPV). PPV samples with 1% S and 5-10% O impurities were obtained whenever the corresponding sulfon ium precursor polymers were subjected to XPS scans prior to thermal co nversion. 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 32 0 degrees C without prior XPS scan. Therefore the S impurities were re sulted from x-ray induced chemical reactions which might involve the f ormation of sulfur ylides. By resolving the O 1s peak,-four types of o xygen species were identified, namely carbonyl (C=0) hydroxy (C-(O) un der bar H) ether (C-(O) under bar-C) and the carboxylic groups(H (O) u nder bar-C = 0). The oxygen groups reacted with Ca to form reversed su rface band bending was found for the S containing PPVs with respect to that for the S free PPVs during the Ca interface formation. Our overa ll results suggest that the barrier height at metal/PPV interface is h ighly sensitive to the surface preparation and relatively insensitive to the work function ofthe metals.