INTERFACE FORMATION OF CA WITH POLY(P-PHENYLENE ALPHA,ALPHA'-DIPHENYL VINYLENE) AND POLY(P-PHENYLENE ALPHA-PHENYLVINYLENE)

We have investigated the interface formation of Ca with poly(p-phenylene alpha,alpha'-diphenyl vinylene) (PPV-DP) and poly(p-phenylene alpha-phenyl vinylene) (PPV-P) using X-ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of Ca-O, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Angstrom of Ca deposition. At the same time, a new C 1s component became noticeable at about -1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form Ca-C species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation, as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Angstrom of Ca overlayer is contaminated by the Ca-O and Ca-C species and the overlayer is pure beyond 15 Angstrom of Ca coverage.