Ion implantation of graphene with keV carbon ions: Defect types, evolution and substrate effects

We study defect formation in chemical vapor deposition grown single layered graphene (SLG) through ion implantation. The SLG is transferred onto SiO2/Si or GaN/sapphire substrate prior to the ion implantation process. Carbon ions with precisely controlled doses and energies are implanted into the SLG by an ion implanter. Micro-Raman, X-ray photoelectron spectroscopies, and Hall measurement are employed to characterize the defects in the implanted SLG. It is found that the defect density and resistance increase, while the defect type exhibits a transition from individual vacancy to extended edge type, as implant doses increase. Through detailed analysis on the peak shift of Raman bands, we found indication of strains formation in the implanted SLG due to the defect formation. Slight structural recovery and relaxation of strain can be achieved through post-annealing in high vacuum. However, unintentional doping through formation of C-O/C-N related bonds is found for the heavily implanted SLG on SiO2/GaN substrates. We discuss the probable defect formation mechanism and evolution in light of the interplay between SLG and the underneath substrates.