Intrinsic superstructure near atomically clean armchair step edges of graphite

摘要

We investigated the electronic superstructure of a graphite surface in the vicinity of monoatomic armchair step edges with scanning tunneling microscopy and spectroscopy. Only the (root 3 x root 3)R30 degrees superstructure is visualized near atomically clean armchair edges, while the honeycomb superstructure is absent. The spectroscopic mapping near the clean armchair edge clearly reveals the (root 3 x root 3)R30 degrees superstructure on both sides of the step edge. We have also visualized a mixture of (root 3 x root 3)R30 degrees and honeycomb superstructures near structurally defective armchair edges. Our results suggest that the honeycomb superstructure pattern results from a superposition of two sets of (root 3 x root 3)R30 degrees superstructures with different phases. Our observation solves the mystery of the coexistence of two types of superstructures reported by prior studies.