Interface formation of Ca with poly( p ‐phenylene α,α′‐diphenyl vinylene) and poly( p ‐phenylene α‐phenyl vinylene)

We have investigated the interface formation of Ca with poly( p ‐phenylene α,α′‐diphenyl vinylene) (PPV‐DP) and poly( p ‐phenylene α‐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 CaO, 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 Å of Ca deposition. At the same time, a new C 1s component became noticable 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 CaC 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 Å of Ca overlayer is contaminated by the CaO and CaC species and the overlayer is pure beyond 15 Å of Ca coverage.