Defect evolution comparison between He+ and He2+ ions irradiation on graphene

This study investigates the role of the projectile's charge state in the defect engineering of graphene using ion beams. A comparison was made between defects induced by He+ and He2+ ions at an identical kinetic energy of 120 keV. Raman spectroscopy analysis showed that He2+ ions generated a higher defect density, ranging from 40 to 65%, compared to He⁺ ions. To investigate how this defect difference impacts device performance, we fabricated and tested chemiresistive gas sensors, where devices irradiated with He2+ showed improved sensitivity to hydrogen. The observation of higher defect generation for He2+ can be explained by the absence of electron screening, which is present for the He⁺ ion. This condition could increase the Coulomb interaction with target carbon nuclei, consistent with a larger Rutherford scattering cross-section. The results indicate that, even within the same ion species, the ion charge state can serve as an additional parameter for modifying the properties of graphene-based devices.