Hydrogenation of Graphene Using Electron Irradiation in Ultra-High Vacuum Studied Using Temperature Programmed Desorption*

There have been numerous reports on the hydrogenation of graphene using electron irradiation to dissociate hydro-molecules such as water on the surface of the sample. These studies have relied primarily on Raman spectroscopy for characterization which is not an element specific technique. We have used Temperature Programmed Desorption (TPD) for this study which is more capable of directly detecting hydrogen. A chemical vapor deposition (CVD) grown graphene sample was annealed to 350° C for 1 hour in an ultra-high vacuum chamber to remove adsorbates. The sample was then exposed to heavy water vapor at a pressure of 12 torr for 1 hour. Heavy water was chosen so that adsorbates emitted from the sample could be distinguished as 4 amu deuterium gas as opposed to 2 amu hydrogen gas emitted from other components inside the chamber. The sample was then irradiated to a dosage of 1×10¹⁷ electrons/cm² with a beam energy of 1.5 keV in situ with a base pressure of 5×10^-10 torr. After irradiation the sample was heated to 100° C while analyzing gas partial pressures using a residual gas analyzer (RGA) for TPD studies. We were able to record the partial pressures of 2 amu and 4 amu gases as a function of time and temperature. Further experiments will be conducted using samples exposed to normal water vapor, ambient air, and possibly other vapors.