A study of graphite surface with stm and electronic structure calculations

Abstract

The (0001) surface of graphite has been investigated using the scanning tunneling microscope (STM) over a relatively wide area containing many unit cells. We do not observe trigonal symmetry but rather find one preferred direction which remains unaffected even by extended defect areas. Corrugations over several ångströms are easily discernible. We have performed an extensive set of self-consistent electronic structure calculations for a monolayer and three-layer graphite slabs with the ideal and slipped configurations. Based on the detailed charge-density analysis we find that the large corrugation arises neither from the total charge density, nor from the local density of states around the Fermi surface. Somewhat larger corrugation (but still smaller than the one observed) and the absence of trigonal symmetry can be explained by an atomic configuration, in which the top layer of graphite is slipped relative to sub-surface layers. Our results point to the fact that the huge corrugation observed may have several origins, one possibility being the elastic deformations induced by the tip.