Real time electron emission dynamics of graphene under proton irradiation

Graphene has a wide range of applications in novel electronics devices, such as transistors, biosensors, and solar cells. However, since its properties can be sensitively influenced by its defects, a precise characterization technique is often required for materials fabrication. Focused ion beams have been widely employed in this context, but their parameters must be carefully selected, which requires a detailed understanding of the underlying excited electron dynamics. Here, we apply a combination of real-time time dependent density functional theory and Ehrenfest dynamics to qualitatively investigate the intensity and duration of secondary electron pulses for graphene under proton irradiation and its dependence on proton trajectory and velocity. We reveal that centroid trajectories yield 38-53% more secondary electrons than channeling trajectories on both sides of the graphene. Also, we find that the duration of secondary electron pulses increases as the proton velocity increases. Recapture of electrons can be observed after 1 fs for protons with kinetic energy near 6.1 keV but after 3 fs for protons with kinetic energy more than 25 keV. This comprehensive description of secondary electron pulses provides critical insight into optimizing the parameters of ion beams.