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Theoretical studies on the scanning tunneling microscope and its spectroscopic version are reviewed. This research has shown that the conductance of the tunneling electrons is strongly influenced by the classical image potential. The introduction of this potential increases the conductance, although the slope of the logarithm of the conductance versus electrode separation remains practically constant. The image force also has focusing effects on the tunneling electrons and produces a minimum in the resolution for ∼5 Å electrode separation. Spectroscopic levels have been calculated for the image states held by the tunneling potential. The results of this work agree very well with experimental data and indicate that the evolution of the observed tunneling spectroscopic levels with applied field is very sensitive to the image potential, and, moreover, that the whole series of image states can be obtained by extrapolation to zero applied field. Work is also presented on the theoretical aspects of tunneling spectroscopy of thin oxide layers grown on a metal substrate—NiO on Ni(100). From theory and experimental data, information can be obtained about the electronic band structure and the number of layers of the oxide. All results of the above research are in accord with the experimental data of Binnig, Rohrer, et al. [1–3]
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