On the imaging mechanism of monatomic steps in graphite

The shape and the atomic arrangement of monolayer steps of graphite have be en characterized by STM. The origin of the appearance of the imaged feature s along the steps is discussed, addressing for the first time both morpholo gical and electronic considerations. Extended Huckel theoretical calculatio ns of nanotubes are used to identify the contribution of the electronic str ucture to the STM image of: monolayer steps. We show that mechanical tip-sa mple interactions dominate the imaging process of graphite, leading to step deformation during scanning and negative STM contrast of the atom position s in the hexagonal unit cell.