Contrast inversion of the apparent barrier height of Pb thin films in scanning tunneling microscopy

Abstract

Scanning tunneling microscopy measurements of the apparent height of the tunneling barrier are analyzed for Pb islands on Ag(111). The apparent barrier height (ABH) significantly varies with the bias voltage. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of the ABH. Using model calculations, these variations are interpreted in terms of the strongly modulated local density of states of thin Pb films, which is caused by quantum well states.