A wide optical-gap in fully sp3-like hydrogenated monolayer graphene

A comprehensive spectroscopic characterisation is reported for two highly hydrogenated monolayer graphene samples transferred onto nickel grids. X-ray photoemission spectroscopy of the C 1s core-level shows that the initially more defective, s p 3 -like graphene sample reaches a 100% s p 3 -like profile after hydrogenation, whereas the flatter, more s p 2 -arranged sample saturates at 60% s p 3 . Low-energy reflection electron energy loss spectroscopy (EELS) corroborates these findings: the π -plasmon excitation is quenched in the fully s p 3 sample and strongly reduced in the partially converted one. The extreme surface sensitivity of low-energy reflection EELS enables extraction of the optical band gap of the hydrogenated layer even on a metallic support, yielding values of 6.3 and 6.2 eV for the two samples. The C–H stretching vibrational mode is also resolved, providing a direct fingerprint of graphene–hydrogen bonding. Finally, valence-band measurements of the 60% saturated sample suggest the coexistence of one-side and two-side hydrogenation morphologies.