Fluence- and Layer-Dependent Defect Formation in CVD-Grown Graphene Under Low-Energy Nitrogen Ion Implantation

Graphene grown by chemical vapor deposition (CVD) on polycrystalline Cu/Si and transferred onto SiO2/Si substrates was subjected to low-energy nitrogen ion implantation (350 eV) at fluences ranging from 1012 to 1016 cm−2 and subsequently investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Extensive Raman mapping performed prior to implantation indicates that the transferred samples consist predominantly of single-layer graphene (SLG), along with small domains of folded graphene (FG) that resemble bilayer graphene (BLG) with effectively random twist angles. At relatively low fluences, nitrogen ion implantation does not induce significant structural modifications in SLG, but leads to only a slight increase in doping compared to unimplanted samples. In contrast, at high ion fluences, SLG undergoes amorphization accompanied by severe damage of the substrate, as evidenced by the presence of an intense photoluminescence signal attributed to implantation-induced defects in the SiO2 layer. Data analysis indicates that, for fluences 1013 and 1014, the implantation-induced defects in SLG are predominantly vacancy-like, with a smaller contribution from sp3-type defects, whereas FG domains appear less sensitive to defect accumulation.