STM/STS observation of peculiar electronic states at graphite edges

The structure-dependent edge state of graphite is investigated by ultra-high-vacuum scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) observations. On a hydrogenated zigzag edge, bright spots assigned to edge states are observed together with a (root 3 x root 3) R30 degrees superlattice. The STS measurement shows that the bright spots originate from a peak near the Fermi level at V-S = -30mV. In contrast, on a hydrogenated armchair edge, such bright spots are not observed. Even in the hydrogenated armchair edge, however, edge states are observed at defect points, where zigzag edges are partially created. The distribution of the edge states is dependent on the detailed structure of the defect. (c) 2006 Elsevier B.V. All rights reserved.