Observation of zigzag and armchair edges of graphite using scanning tunneling microscopy and spectroscopy

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to reveal structure-dependent edge states in graphite, showing that zigzag edges host edge states while armchair edges do not, with observations of defect-induced zigzag segments.

Contribution

It provides direct STM/STS evidence of edge state differences between zigzag and armchair graphite edges, including effects of hydrogenation and defects.

Findings

Zigzag edges exhibit edge states near the Fermi level.

Armchair edges lack significant edge states under the same conditions.

Defects in armchair edges can create localized zigzag segments.

Abstract

The presence of structure-dependent edge states of graphite is revealed by both ambient- and ultra-highvacuum- (UHV) scanning tunneling microscopy (STM) / scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag (armchair) edge, bright spots are (are not) observed together with (SQRT(3) by SQRT(3))R30 superlattice near the Fermi level (V_S = −30 mV for a peak of the local density of states (LDOS)) under UHV, demonstrating that a zigzag edge is responsible for the edge states, although there is no appreciable difference between as-prepared zigzag and armchair edges in air. Even in hydrogenated armchair edge, however, bright spots are observed at defect points, at which partial zigzag edges are created in the armchair edge.