Apparent tunneling barrier height and local work function of atomic arrays

Spatially resolved measurements of the apparent tunneling barrier height Φ(app) in scanning tunneling microscopy have been used to estimate variations of the local work function Φ of surface structures. We experimentally show that Φ(app) can fail as a measure of Φ. The discrepancies are attributed to a kinetic-energy contribution to Φ(app). This contribution depends on the lateral extent of the tunneling current filament and, consequently, on the local surface structure.