  Laterally localized electronic states are identified on a single layer of
graphene on ruthenium. The individual states are separated by 3 nm and comprise
regions of about 90 carbon atoms. This constitutes a quantum dot array,
evidenced by quantum well resonances that are modulated by the corrugation of
the graphene layer. The quantum well resonances are strongest on the isolated
"hill" regions where the graphene is decoupled from the surface. This peculiar
nanostructure is expected to become important for single electron physics where
it bridges zero-dimensional molecule-like and two-dimensional graphene on a
highly regular lattice.
