  Graphene nano-flakes (GNFs) are predicted to host spin-polarized metallic
edge states, which are envisioned for exploration of spintronics at the
nanometer scale. To date, experimental realization of GNFs is only in its
infancy because of the limitation of precise cutting or synthesizing methods at
the nanometer scale. Here, we use low temperature scanning tunneling microscope
(STM) to manipulate coronene molecules on a Cu(111) surface to build artificial
triangular and hexagonal GNFs with either zigzag or armchair type of edges. We
observe that the metallic edge states only exist in the GNFs with zigzag edge
and localize at the most outside one type of the sublattice. The experimental
results agree well with the tight-binding calculations. To our knowledge, our
work renders the first systematic experimental confirmation of the predicated
electronic properties of the GNFs.
