  The growth of single layer graphene nanometer size domains by solid carbon
source molecular beam epitaxy on hexagonal boron nitride (h-BN) flakes is
demonstrated. Formation of single-layer graphene is clearly apparent in Raman
spectra which display sharp optical phonon bands. Atomic-force microscope
images and Raman maps reveal that the graphene grown depends on the surface
morphology of the h-BN substrates. The growth is governed by the high mobility
of the carbon atoms on the h-BN surface, in a manner that is consistent with
van der Waals epitaxy. The successful growth of graphene layers depends on the
substrate temperature, but is independent of the incident flux of carbon atoms.
