  Since the advent of graphene ushered the era of two-dimensional materials,
many forms of hydrogenated graphene have been reported, exhibiting diverse
properties ranging from a tunable band gap to ferromagnetic ordering. Patterned
hydrogenated graphene with micron-scale patterns has been fabricated by
lithographic means. Here we report successful millimeter-scale synthesis of an
intrinsically honeycomb patterned form of hydrogenated graphene on Ru(0001) by
epitaxial growth followed by hydrogenation. Combining scanning tunneling
microscopy observations with density-functional-theory (DFT) calculations, we
reveal that an atomic-hydrogen layer intercalates between graphene and
Ru(0001). The result is a hydrogen honeycomb structure that serves as a
template for the final hydrogenation, which converts the graphene into graphane
only over the template, yielding honeycomb-patterned hydrogenated graphene
(HPHG). In effect, HPHG is a form of patterned graphane. DFT calculations find
that the unhydrogenated graphene regions embedded in the patterned graphane
exhibit spin-polarized edge states. This type of growth mechanism provides new
pathways for the fabrication of intrinsically patterned graphene-based
materials.
