  We investigated the electronic superstructure of graphite surface in the
vicinity to monoatomic armchair step edges with scanning tunneling microscopy
and spectroscopy. Only the ($\sqrt{3}\times\sqrt{3}$)$\textit{R}$30$^{\circ}$
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
($\sqrt{3}\times\sqrt{3}$)$\textit{R}$30$^{\circ}$ superstructure on both sides
of the step edge. We have also visualized a mixture of
($\sqrt{3}\times\sqrt{3}$)$\textit{R}$30$^{\circ}$ and honeycomb
superstructures near structurally defective armchair edges. Our results suggest
that the honeycomb superstructure pattern results from superposition of two
sets of ($\sqrt{3}\times\sqrt{3}$)$\textit{R}$30$^{\circ}$ superstructure with
different phases. Our observation solves the mystery of the coexistence of two
types of superstructures reported by prior studies.
