Abstract
Spatially resolved measurements of the apparent tunneling barrier height Φapp in scanning tunneling microscopy have been used to estimate variations of the local work function Φ of surface structures. We experimentally show that Φapp can fail as a measure of Φ. The discrepancies are attributed to a kinetic-energy contribution to Φapp. This contribution depends on the lateral extent of the tunneling current filament and, consequently, on the local surface structure.
Highlights
Atomic steps are a well-known example of a structure that affects the local work function Φ
The work function of a metal surface [1], the work required at temperature T = 0 K to move an electron from the metal to infinity, is relevant for, e.g.,the behavior of electronic devices [2], the energetics of molecules at surfaces [3], including reactions [4,5], and electronic states confined near surfaces [6]
I(z) data from Cu atoms arranged in extended single-atom rows and double rows as well as from trenches of single-atom depth are analyzed. Φapp determined from these data varies significantly, but the variation is opposite to the expected trend of the local sample work function
Summary
Atomic steps are a well-known example of a structure that affects the local work function Φ. In the most simple onedimensional model the exponential variation of the tunneling current I at low bias with the tip–sample distance z is directly related to the average of the work function of the tip and the sample [21,22]. There is no simple expression connecting Φapp and the local work function of the sample Φ (partially because the tip structure is usually unknown), it is Beilstein J.
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