Mobility of Single Vacancies and Adatoms in Graphene at Room Temperature

We investigate the mobility of structural defects, adatoms and defect-adatoms combination in self-supporting graphene subjected to keV ion irradiation. In a first scenario, homogeneous irradiation using 20 keV Ar⁺ ions at a dose of 3 × 10¹⁴ ions cm^-2 induces tensile strain of up to 0.8%. This strain diminishes with increasing defect density at a dose of 5 × 10¹⁴ ions cm^-2, indicating a strain-relaxation mechanism. Contrary to the expected localized behavior, vacancies exhibit long-range interactions, contributing to global strain effects across the lattice. In a second scenario, by employing a nanopore mask, we spatially confined defect generation to periodically aligned circular regions surrounded by non-irradiated material, enabling direct observation of vacancy and adatom dynamics. Selected area electron diffraction (SAED) reveals significant structural damage in areas adjacent to irradiated regions, suggesting that single vacancies migrate over distances on the order of 100 nm from irradiated to non-irradiated zones even at room temperature. The build-up of lattice strain observed here may play a key role in lowering the migration barrier of single vacancies, thereby facilitating their diffusion into pristine lattice regions. Furthermore, our findings highlight the role of preexisting surface contaminants in preserving lattice integrity through a self-healing mechanism, where adatominduced lattice reconstruction mitigates defect-induced structural degradation.