▎ 摘　　要

Scanning tunneling microscopy (STM) is adopted to characterize the commonly formed armchair edge structure of epitaxial graphene prepared by thermal decomposition of 6H-SiC. At the smooth armchair edges, root 3 x root 3 patterns are usually observed as a result of quantum interference (QI) of the incident and directly reflected Bloch waves of electrons at the Fermi level and, the distinct morphologies, such as, dumbbell- and horseshoes-shaped ones can be ascribed to the phase shift of the reflected Bloch wave. However, atomically-resolved graphene lattice instead of QI patterns is imaged near the ridged armchair edges. On the analogy of light interference, when the electron waves encounter such a "rough" edge, diffuse reflection occurs and coherent conditions between the incident and reflected waves cannot be satisfied and so no QI pattern is observed. This provides a unified model describing the electronic states on graphene edges and facilitates optimal design of graphene-based electronics.