POLARIZATION OF ELECTRONIC CHARGE AND DISTORTION OF SURFACE GEOMETRY BY A SCANNING TUNNELING MICROSCOPY TIP - SI(100)

First-principles calculations have been performed of (a) the electronic structure, (b) the Hellmann-Feynman forces, and (c) the distortion of the surface geometry at a Si(100) surface when a voltage is applied by a model scanning tunneling microscopy (STM) tip. As one expects, a polarization charge forms under the tip at the semiconductor surface. For the voltages and distances typical of STM experiments, and corresponding to electric fields of approximately 0.1 V/angstrom, the electronic structure is only weakly perturbed and the surface atoms are displaced by only a few hundredths of an angstrom. These results rule out tip-induced perturbations of the surface as an explanation for the symmetric dimer images seen in STM experiments on Si(100).