▎ 摘　　要

Scanning tunneling microscopy is used to study the edge orientation of graphene fabricated by thermal decomposition of 6H-SiC. The exploration on the atomically resolved structures and the patterns in reciprocal space demonstrates that the armchair direction is always parallel to the basic vector of 6 x 6 reconstruction as well as the close-packed direction of 6H-SiC substrate. This can be used as the criterion to characterize the edge direction of graphene. With this method, it is found that armchair edges are preferred in both monolayer and bilayer regions. This special edge certainly will affect the electronic states and consequently the properties. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769967]