Local electric field effects in STM of single-atom adsorption on a Si(001) surface

Abstract

The effect of the tip-induced electric field on STM images and spectra from a Si(001) surface on which Sb, Na and K atoms were adsorbed at low coverage was studied by total-energy LDF calculations. The adsorption geometry of Na and K atoms on the Si(001) surface was found to be strongly field-dependent. In contrast, the adsorption geometry of Sb on the Si(001) surface was almost insensitive to the field. The different topographic and electronic responses of different atoms in the surface resulted in changes in the relative contrast of the adsorbed atoms and the substrate in STM images. The calculated filled-state images were found to be similar to reported experimental images [Y.W. Mo, Phys. Rev. Lett. 65 (1990) 3417; A. Brodde, Th. Bertrams, H. Neddermeyer, Phys. Rev. B 47 (1993) 4508]. We found that the electric field inhibits empty-states imaging of alkali metals on Si(001) surface. Possible distortions of the tunneling spectra are discussed. Our results demonstrate that the tip-induced electric field is an important factor in forming STM data, and cannot be neglected in the interpretation of STM images and spectra.