  Topographic scanning tunneling microscopy (STM) images of epitaxial single
layer graphene on the Rh(111) surface reveal that extended single crystalline
graphene domains are produced without any defects on a large scale. High
resolution imaging shows that the moir\'e structure resulting from the lattice
mismatch between the Rh(111) substrate and graphene is highly corrugated,
containing regions of an additional spatial modulation in the moir\'e supercell
compared with those previously reported for graphene on Ir(111) or graphene on
Ru(0001). These areas, which correspond to the "bridge" regions of the moir\'e
structure appear as depressions in STM images indicating a strong orbital
hybridization between the graphene layer and the metallic substrate.
Valence-band photoemission confirms the strong hybridization between graphene
and Rh(111) which leads to the pronounced corrugation of the graphene layer.
Our findings underline the importance of considering substrate effects in
epitaxially grown graphene layers for the design of graphene-based nanoscale
systems.
