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Scanning Tunneling Spectroscopy of Insulating Films

Paper for Advanced Solid State Physics class, Dmitri Y. Petrovykh.

Physics Department, University of Wisconsin, Madison, WI, USA (1999)

  1. 1 STM and STS of Bulk Insulators
    2 STS of Thin Film Insulators
  2. 1 Tunneling Current Theory
    2 Tunneling Barrier Parameters
    3 The Simplest Model for T(E,V)
    4 Thermal Broadening Included
    5 More Accurate Tunneling Probabilities
  3. Possible Additional Effects
  4. Acknowledgments & References

II.2 Tunneling Barrier Parameters

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) = tunneling probability, where a-term

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.

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