Abstract
A new model of field emission in a scanning tunnelling microscope was developed. The model describes the tunnelling current from a surface of semiconductor (semimetal) and allows estimating the preexponential factor in the expression for the tunneling probability. It is shown that this factor is directly related to the degree of localization of the electron density and determines the shape of the local tunnel current-voltage characteristics (LTCVCs) at low voltages. The model allows separating the contributions of surface electronic states of different symmetry (dimension) of the tunnelling current. The practical application of the model is demonstrated by the example of mathematical processing of the LTCVCs of HOPG surface containing different structural defects.
Highlights
The processes of assembling two-dimensional monolayers of organic molecules constantly attract the attention of researchers
It is well known that the defects on the surface of solids are active sites in catalysis, adsorption and nucleating centers of a new phase [1,2,3], because it is on them free electrons are localized [4]
In electric field the tunneling probability p can be written in a universal form, where D – is a constant that does not depend on the external field [7, 11]
Summary
The processes of assembling two-dimensional monolayers of organic molecules constantly attract the attention of researchers. At low electric fields electron emission from the semiconductor surface, when is measured by probe microscopy techniques, is a particular case of the tunnelling effect [6]. Such processes are usually studied with the semi-classical approximation that determines the amplitude of the transition up to an exponential factor. In this voltage range electric field only slightly reduces the average height of the potential barrier at solid surface and its strength disappears from the exponent of the estimated CVC. In electric field (this corresponds to the length l of the triangular potential barrier, i.e., the potential barrier on the right side in Figure 1 is the probe potential) the tunneling probability p can be written in a universal form, where D – is a constant that does not depend on the external field [7, 11]
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