On the imaging mechanism of monatomic steps in graphite

The shape and the atomic arrangement of monolayer steps of graphite have been characterized by STM. The origin of the appearance of the imaged features along the steps is discussed, addressing for the first time both morphological and electronic considerations. Extended Huckel theoretical calculations of nanotubes are used to identify the contribution of the electronic structure to the STM image of monolayer steps. We show that mechanical tip–sample interactions dominate the imaging process of graphite, leading to step deformation during scanning and negative STM contrast of the atom positions in the hexagonal unit cell.