  The growth, atomic structure, and electronic property of trilayer graphene
(TLG) on Ru(0001) were studied by low temperature scanning tunneling microscopy
and spectroscopy in combined with tight-binding approximation (TBA)
calculations. TLG on Ru(0001) shows a flat surface with a hexagonal lattice due
to the screening effect of the bottom two layers and the AB-stacking in the top
two layers. The coexistence of AA- and AB-stacking in the bottom two layers
leads to three different stacking orders of TLG, namely, ABA-, ABC-, and
ABB-stacking. STS measurements combined with TBA calculations reveal that the
density of states of TLG with ABC- and ABB-stacking is characterized by one and
two sharp peaks near to the Fermi level, respectively, in contrast to the
V-shaped feature of TLG with ABA-stacking. Our work demonstrates that TLG on
Ru(0001) might be an ideal platform for exploring stacking-dependent electronic
properties of graphene.
