Influence of electron energy on defect formation in graphene: Insights from the local activation model

We investigate the effects of electron beam energy on defect formation in monolayer graphene using Raman spectroscopy and the local activation model. Monolayer graphene samples were irradiated at beam energies ranging from 1 to 30 keV, and the evolution of Raman D, G, and D’ peaks was monitored as a function of electron fluence. For all energies, the ID/IG and ID′/IG ratios exhibited a two-stage behavior, initially increasing with fluence before decreasing at higher defect densities, consistent with the local activation model predictions. Notably, the maximum ID/IG ratio decreased and shifted to a higher fluence with increasing beam energy. At lower beam energies (1–2 keV), an additional broad Raman peak was observed near the G peak, attributed to carbonaceous film deposition from secondary electrons (SEs). Defect formation was modeled using the local activation model with adjustments to account for SE-induced dissociation of surface adsorbates, showing good agreement with experimental data. Parameters A and B, which represent the incident electron fluence required to generate a defect-active region and the fraction of dissociable adsorbates, respectively, showed systematic trends with beam energy. Postirradiation annealing studies were conducted to determine activation energies for defect healing via Arrhenius analysis. The extracted activation energies (0.31–0.48 eV) are consistent with sp3-type defects such as hydrogen and hydroxyl groups with attached water molecules. These findings highlight the critical role of beam energy and SE yield in the defect engineering of graphene and demonstrate the utility of the local activation model in quantitatively describing beam-induced disorder.