Thermal relaxation of ion-irradiation damage in graphite

The thermal-relaxation rate of disorder produced in graphite irradiated by 3-keV He⁺ is studied using real-time Raman measurements at sample temperatures from room temperature to 573 K. Results indicate that two relaxation processes occur, i.e., a fast-rate process with an activation energy of 0.89±{}0.10 eV and a slow-rate process at 1.8±{}0.3 eV. The fast and slow processes are, respectively, suggested to be a recombination of vacancies-interstitials and a vacancy clustering process which occurs during diffusion of vacancies in the graphite plane.