Tunneling asymmetries in doped Al-AlOx-Pb junctions

Asymmetries in both the elastic and inelastic electron tunneling components of Al-$\mathrm{Al}{\mathrm{O}}_x$-Pb junctions doped with organic ring compounds have been examined. The barrier shapes and heights and the correlated behavior of the elastic characteristic curves and the inelastic vibrational modes are unusually sensitive to differences in molecular components and the resulting interface structure of the junction. Model barriers fitted with a computer program adequately fit the large variations in ± bias asymmetry of the elastic tunneling component observed for different molecules. Asymmetries in the inelastic mode intensity generally indicate an agreement with a long-range potential interaction between the molecule and tunneling electron. Enhanced asymmetry in inelastic mode intensity is observed for some cases which also show usually low effective organic barriers and a correlated effect on mode coupling.