STM/STS observations of zigzag and armchair edges of graphite

Abstract

The presence of structure-dependent edge states of graphite has been revealed by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) observations under ultrahigh vacuum. On a hydrogen-terminated zigzag edge, at a bias voltage near the Fermi energy, bright spots are observed in STM images, demonstrating that the zigzag edge is responsible for the edge states. The edge states at the zigzag edge show different spatial distributions depending on whether the edge atoms are the α-or β-edge carbon termination and on the size of thezigzag edge. The amplitude of the edge state around the structural defects in an armchair edge often has a prominent hump spreading in a direction determined by local atomic structure of the edge. The tight binding calculation based on the atomic arrangements observed by STM well reproduces the observed spatial distribution of the local density of states.