Plasma Hydrogenation of n-Layer Graphene

We propose a new mechanism for the hydrogenation of mono-, bi-, and tri-layer graphene samples using an H$_{2}$ plasma. We find that hydrogenation occurs as a result of electron irradiation of H$_{2}$O adsorbates on the sample rather than H species from within the plasma. We propose that the mechanism is electron-impact fragmentation of the H$_{2}$O adsorbates occurring naturally above and below the sample. The stability of the hydrogenation increases with the incident electron energy, allowing for hydrogenated samples that are stable at temperatures $>$ 200 $^{\circ}$C. We also observe fully hydrogenated bi- and tri-layer graphene, which may be evidence for new materials, diamane and \textit{triamane}. Diamane, a two atom thick layer of hydrogenated diamond, is predicted to have a band gap of 3.12 eV and be stronger than graphane, hydrogenated graphene.