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 investigation s of the interface formation of Al with poly(p-phenylene vinylene) (PP V) prepared under various conditions. We have found that during deposi tion Al reacts with residual hydroxyl groups in the polymer. In additi on, we have found that Schottky barrier formation and the associated b and 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 li ttle as 1 angstrom Al. By contrast, a sample converted ex situ, with 1 0% surface oxygen, is insensitive to aluminum deposition. In view of t he results obtained, we feel that surface impurities and adsorbed spec ies may delay Schottky barrier formation by acting as a buffer layer w hich prevents the PPV substrate from interacting with the growing laye r of Al. In the in situ samples where band bending occurs, we find tha t it takes place after the formation of metallic Al.