AN X-RAY PHOTOEMISSION SPECTROSCOPY STUDY OF THE ROLE OF SAMPLE PREPARATION ON BAND BENDING AT THE INTERFACE OF AL WITH POLY(P-PHENYLENE VINYLENE)

We report on our recent x-ray photoemission spectroscopy investigations of the interface formation of Al with poly(p-phenylene vinylene) (PPV) prepared under various conditions. We have found that during deposition Al reacts with residual hydroxyl groups in the polymer. In addition, we have found that Schottky barrier formation and the associated band bending depend strongly on surface preparation. Samples converted in situ, containing 5% surface oxygen, show band bending that depends on the thickness of the Al overlayer, with effects arising after as little as 1 angstrom Al. By contrast, a sample converted ex situ, with 10% surface oxygen, is insensitive to aluminum deposition. In view of the results obtained, we feel that surface impurities and adsorbed species may delay Schottky barrier formation by acting as a buffer layer which prevents the PPV substrate from interacting with the growing layer of Al. In the in situ samples where band bending occurs, we find that it takes place after the formation of metallic Al.