Hydrogenation of Graphene Using Electron Irradiation in Ultra-High Vacuum Studied Using X-Ray Photoelectron Spectroscopy

There have been numerous reports on the hydrogenation of graphene using electron irradiation in the 10-20 keV electron energy range. Most of these studies have relied on Raman spectroscopy for characterization which is not an element specific technique. We have used X-Ray photoelectron spectroscopy (XPS) for this study which is a more element sensitive technique. Chemical vapor deposition grown graphene samples were irradiated to a dosage of 1×10¹⁷ electrons/cm² with a beam energy of 1.5 keV in an ultra-high vacuum (UHV) chamber at a base pressure of 3×10^-10 torr. After irradiation the samples were removed from the UHV chamber and placed in a different chamber for XPS studies. The C1s XPS peak showed that before irradiation the sample mostly showed sp² type carbon and hydroxyl (C-OH). After irradiation, we found that the XPS spectra corresponded to a higher proportion of sp³ carbon due to C-H₂ than sp² carbon. We then removed the sample, annealed it in a tube furnace at 270° C for 10 minutes under dry nitrogen and performed XPS. We placed the same sample back in the UHV system and irradiated it under similar conditions as before. We then did XPS again and observed the same effect that after irradiation, the mostly sp² carbon and C-OH changed to mostly sp³ carbon associated with C-H₂. We attribute hydrogenation to the electron induced dissociation of adsorbed water or the C-OH.