Structure of hydrogen-dosed graphene deduced from low electron energy loss characteristics and density functional calculations

We employed nanometer-scale spatially resolved electron energy loss spectroscopy to monitor the degree and localization of electronic passivation of graphene surfaces by using the $π$-plasmon as an indicator of $sp2$-bonding. Upon hydrogenation, the $π$-plasmon does not vanish, and a new feature at 7 eV occurs in the spectra. This behavior conforms to the theoretical electron energy loss spectra derived from density functional calculations for partial hydrogenation, with benzene rings assuming a corrugated structure. The spatial distribution of the spectral features and atomic resolution Z-contrast images indicate absence of any long-range ordering in the hydrogenated areas.