Apparent tunneling barrier height and local work function of atomic arrays.

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