Electric field effects in scanning tunneling microscopy

We have developed a theory for tunneling between a surface and a model probe tip, including the effect of a finite electric field between the tip and the surface, and applied the theory to understand STM experiments of the hydrogen passivated Si(100) surface. The theoretical model is based on first principles electronic structure calculations and has no adjustable parameters. We have applied the theory to obtain theoretical STM images at relativily high voltages (2-3V) of the monohydrate Si(100) surface with missing hydrogen defects, and found excellent agreement with experimental images. However, our main goal is to use the theory to understand experimental measurements of current and voltage dependence in STM induced desorption of hydrogen. We have found that experimental measured iso-lines of constant desorption probability in the I-V plane coincide with iso-lines of constant electric field, indicating a strong dependence of the desorption mechanism upon the electric field between the tip and the sample.