Influence of STM tip on electronic structure: Si(100) dimers
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There are strong reasons for believing that dimers in defect-free regions of the Si(100) surface are asymmetric (tilted), but they appear to be symmetric in STM images. It has been suggested that these symmetric images result from a strong distortion of the dimer's electronic structure (and, as a consequence, its geometry) when the STM voltage is applied. Here we report first-principles calculations for the Si(100) surface in the presence of a voltage applied by a simple model of an STM tip: a uniform sphere of charge, 1.06 Å in diameter and centered 2.5 Å above the surface. For voltages comparable to those used in STM experiments, there is only a very small distortion of the electronic structure, both below and above the Fermi energy E F . Even for large applied voltages, the results indicate that the STM images should be far from symmetric. On the other hand, the time-averaged charge densities for rapidly flipping asymmetric dimers are fully consistent with the STM observations. © 1992.
author list (cited authors)
Huang, Z., & Allen, R. E.