Atomic hydrogen adsorbate structures on graphene.

The adsorbate structures of atomic hydrogen on the basal plane of graphene on a SiC substrate is revealed by Scanning Tunneling Microscopy (STM). At low hydrogen coverage the formation of hydrogen dimer structures is observed, while at higher coverage larger disordered clusters are seen. We find that hydrogenation preferentially occurs on the protruding/high tunneling probability areas of the graphene layer modulated by the underlying 6 x 6 reconstruction of SiC. Hydrogenation offers the interesting possibility to manipulate both the electronic and chemical properties of graphene.