Inelastic electron-tunneling study of barriers grown on aluminum

Abstract

Inelastic electron tunneling has been used to systematically study the techniques used to grow barriers on aluminum films when preparing aluminum-barrier-lead junctions. The hydroxyl and hydrocarbon content of a barrier was found to depend upon the method of preparation as well as the materials used. The spectra for barriers grown either in an oxygen-helium or water-vapor glow discharge were found to contain OH but not CH bands, while the spectra for those grown thermally either in oxygen or water contained both OH and CH bands. Barriers formed by pipetting water onto aluminum had a spectrum which contained OH and CH bands. The effect of using a glow discharge technique was examined by exposing several barriers to an argon glow discharge before depositing the lead electrode. The argon discharge treatment was found to remove all traces of CH bands from the spectra for these barriers. Finally, The problem of choosing a background spectrum when doing spectroscopic studies of doped junctions was examined. Several barriers were prepared by pipetting a few drops of an aqueous glycine solution onto freshly evaporated aluminum. The spectra for the doped barriers were found to contain OH bands similar to the OH bands for an oxygen-helium discharge grown barrier, and CH similar to those for a barrier grown by pipetting water.