REAL-TIME OBSERVATION OF THERMAL RELAXATION OF INITIAL DAMAGE IN GRAPHITE UNDER ION IRRADIATION

Real-time Raman measurements are conducted for graphite during and aft er helium ion and deuterium ion irradiation at the sample temperatures from 393 to 473 K. A transient behavior is observed in the thermal re laxation of lattice disorder. Results indicate that two processes exis t for the restoration of the phonon correlation length by thermal rela xation. The fast process is suggested to be a recombination of vacanci es and interstitials, and the activation energies have similar values: 0.89 +/- 0.10 eV for helium ion irradiation and 1.0 +/- 0.10 eV for d euterium ion irradiation. The slow process suggests a chemical effect; the activation energy for deuterium ion irradiation (0.36 +/- 0.25 eV ) is smaller than that for helium ion irradiation (1.8 +/- 0.30 eV).