Physics Department, University of Wisconsin, Madison, WI, USA (1999)
The first approximation is to assume that both the tip and the sample are essentially metallic and have the same work function φ and constant density of states. The assumption of a constant tip density of states is often made, lacking detailed knowledge of the tip states. The Si density of states has little structure at the energies under consideration, i.e., about 4 eV above the valence band maximum.
Assume that the tunneling probability through the vacuum is given by:
Tvac(E,V) = , where
which corresponds to WKB approximation for tunneling through a barrier of the average height.
Assume that the total tunneling probability T(E,V) = Tvac(E,V)Tins(E,V).
The following are the values of the "fixed" tunneling barrier and environment parameters:
These are the values used in all the following models, unless specified otherwise.