Characterization of the poly(para-phenylene vinylene)-chromium interface by attenuated total reflection infrared and X-ray emission spectroscopies

We have studied the interfaces formed between poly(para-phenylene vinylene) (PPV) thin film and a Cr layer deposited under vacuum by thermal evaporation. Comparison of attenuated total reflection infrared spectra obtained in pristine and Cr-covered PPV films shows that new absorption bands emerge at 687, 1026 and 1392 cm−1 as a consequence of Cr deposition. The Cr(3d) valence distribution from electron-induced X-ray emission measurement on a Cr-covered PPV sample is shifted by 0.9 eV with respect to Cr metal. The new features found in both experiments are interpreted as characteristics of the compound in the polymer-Cr interface. In the case of PPV deposited on Cr no change is observed. Positioning the Fermi level relative to the Cr valence spectral distribution in both polymer-metal and metal-polymer interfaces from X-ray and X-ray photoelectron spectroscopy (XPS) analyses yields a possible explanation for the electrical behavior of the PPV-based diodes.