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 investigation s of the interface formation of metals with poly(p-phenylene vinylene) (PPV) prepared under various conditions. We have found that during de position tbe metal reacts with residual hydroxyl groups in the polymer . In addition, we have found that Schottky barrier formation and the a ssociated bad bending depend strongly on surface preparation. in the c ase 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 oxyg en, is insensitive to aluminium deposition. We feel that surface impur ities and adsorbed species may delay Schottky barrier formation by act ing as a buffer layer that prevents the PPV substrate from interacting with the growing layer of Al. By contrast, the Ca/PPV surface exhibit s delayed band bending, with strong interactions between surface oxyge n and Ca, Our results indicate that band bending at the metal/PPV inte rface is governed by the metallicity of the metal overlayer, which its elf is influenced by the interface reaction of the deposited metal wit h the PPV substrate or the surface residual impurities. Finally, the d egree of band bending observed did not correlate directly with the dif ferences in work functions between the metals and PPV.