Schottky barrier formation at the Ca/poly(p-phenylene vinylene) interface and its role in tunneling at the interface

We have studied the formation of the Ca/poly(p-phenylene vinylene) (PPV) interface using X-ray photoelectron emission spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). The rigid shift seen by XPS in the C(ls) core level spectra of PPV points clearly to charge transfer and Schottky barrier formation at the interface as a result of Ca deposition. The NEXAFS spectra suggest that charge transfer at the metal/polymer interface induces the formation of a bipolaron lattice at the interface. Taken together, these results imply that the metal/polymer interface is not rigid and that triangular barrier tunneling fails to take into account the effect of barrier formation. We propose a band bending modified tunneling model to explain charge transfer at the Ca/polymer interface.