The nature of the oxide barrier in inelastic electron tunneling spectroscopy

We have investigated the insulating barrier of A1-oxidized A1Pb tunnel junctions. This study was effected by measuring the inelastic electron tunneling (IET) spectra of various junctions in which the insulator was formed by oxidizing the aluminum either in an O2 H2O or D2O plasma discharge at various temperatures between room temperature and 250°C. We found that those insulators formed at all temperatures in 02 and those formed at high temperatures (≳150°C) in H2O and D2O are aluminum oxide with no evidence for any appreciable bulk hydroxide. The surfaces of these insulators do have adsorbed hydroxyl groups present, however. The insulators made at lower temperatures (