Hydrogen on graphene investigated by inelastic neutron scattering

Inelastic neutron scattering experiments and ab-initio calculations have been used to investigate the vibrational modes, in a wide energy region between 0 and 200 meV, of hydrogenated graphene produced by chemical method. The results show the presence of atomic hydrogen chemisorbed at the graphene surface. At 10 K, the measured high energy density of states is remarkably similar to that of hydrogenated ball-milled graphite, in which hydrogen is most likely bonded to C atoms at the edges. In fact, in both hydrogenated graphene and hydrogenated ball-milled graphite, the high frequency modes (100-200 meV) show strong similarities with the C-H bending modes of the coronene molecule, in which hydrogen is bonded at the edges. This hypothesis has been supported by ab-initio calculations.