X-RAY PHOTOEMISSION SPECTROSCOPY STUDY OF BAND BENDING AT THE INTERFACE OF METAL WITH POLY(P-PHENYLENE VINYLENE)

We report on our recent x-ray photoemission spectroscopy investigations of the interface formation of metals with poly(p-phenylene vinylene) (PPV) prepared under various conditions. We have found that during deposition tbe metal reacts with residual hydroxyl groups in the polymer. In addition, we have found that Schottky barrier formation and the associated bad bending depend strongly on surface preparation. in the case of Al deposition, samples converted in situ, containing 5% surface oxygen, show band bending that depends on the thickness of the metal overlayer, with effects arising after as little as 1 Angstrom of metal. On the other hand, a sample converted ex situ, with 10% surface oxygen, is insensitive to aluminium deposition. We feel that surface impurities and adsorbed species may delay Schottky barrier formation by acting as a buffer layer that prevents the PPV substrate from interacting with the growing layer of Al. By contrast, the Ca/PPV surface exhibits delayed band bending, with strong interactions between surface oxygen and Ca, Our results indicate that band bending at the metal/PPV interface is governed by the metallicity of the metal overlayer, which itself is influenced by the interface reaction of the deposited metal with the PPV substrate or the surface residual impurities. Finally, the degree of band bending observed did not correlate directly with the differences in work functions between the metals and PPV.