Influence of band structure on the apparent barrier height in scanning tunneling microscopy

The apparent height of the tunneling barrier in scanning tunneling microscopy measured on Au(111), Ag(111), and Cu(111) surfaces is found to vary significantly with the bias voltage. In particular, the apparent barrier height phi(a) is asymmetric with respect to the bias polarity on all three surfaces, in contrast to simple interpretations of phi(a) in terms of an average work function of tip and sample. Model calculations of the tunneling current, which take band-structure effects into account, describe the experimental observations.