Effect of damage cascades on the irradiation-induced amorphization in graphite

In-situ observation of the irradiation-induced amorphization and measurements of the critical amorphization dose in graphite under irradiation with ions and electrons have been performed to reveal the effects of damage cascades. The critical amorphization dose (D_c) increases exponentially with temperature and shows an apparent critical amorphization temperature (T_c). T_c increases with increase in mass of projectiles and with decrease in energy of ions. Dose rate dependence of D_c and T_c was also observed. No amorphization was detected above 860 K. Accumulation of vacancies and/or interlayer carbon molecules is attributable to the amorphization, while annealing of amorphous regions is dominated by kinetics of lattice defects. Defect annealing is associated with recombination of interlayer carbon molecules with vacancies. Damage cascades leave high density of interlayer molecular clusters ((C₂)_n, n=1, 2, 3...) and stable di-vacancies, resulting in stable amorphous regions at high temperature.