H⁺ ion-induced damage and etching of multilayer graphene in H₂ plasmas

H⁺ ion-induced damage of multilayer graphene (MLG) is investigated using Molecular Dynamics simulations as H₂ plasmas could provide a possible route to pattern graphene. Low-energy (5-25 eV) H⁺ cumulative bombardment of ABA-stacked MLG samples shows an increase of the hydrogenation rate with the ion dose and ion energy. At 5 eV, the H coverage grows with the ion fluence only on the upper-side of the top layer but saturates around 35%. Hydrogenation of multi-layers and carbon etching are observed at higher energies. Layer-by-layer peeling/erosion of the MLG sample is observed at 10 eV and occurs in two phases: the MLG sample is first hydrogenated before carbon etching starts via the formation of CH_x (∼60%) and C₂H_x (∼30%) by-products. A steady state is reached after an ion dose of ∼5 × 10¹⁶ H⁺/cm², as evidenced by a constant C etch yield (∼0.02 C/ion) and the saturation of the hydrogenation rate. At 25 eV, an original etching mechanism - lifting-off the entire top layer - is observed at low fluences due to the accumulation of H₂ gas in the interlayer space and the absence of holes/vacancies in the top layer. However, as the underneath layers contain more defects and holes, this Smartcut-like mechanism cannot be not repeated and regular ion-assisted chemical etching is observed at higher fluences, with a yield of ∼0.05 C/ion.