Behavior of deuterium atoms implanted in graphite has been investigated by ERD (elastic recoil detection) method and the defect behavior has also been studied by positron annihilation method. It was found that diffusion of deuterium atoms shows a significant anisotropy, i.e., very high diffusivity along the direction parallel to the basal plane and very low diffusivity along the direction perpendicular to the basal plane. Deuterium atoms are considered to be trapped at the boundaries between adjacent crystallites and the sites of radiation induced defects and are released from the specimen through three stages in the isochronal annealing process depending on the depth of the trapping potential. The isochronal annealing curve of the positron lifetime for HOPG irradiated with electrons at 77 K can be divided into two stages, i.e., below 1200°C and above 1200°C. In the former the increase of positron lifetime corresponding to the growth of interstitital type loops is observed and in the latter that corresponding to the growth of vacancy type loops (and also to interstitial type loops) is observed. Positron lifetime calculation for a vacancy and vacancy clusters was made and the comparison with the experimental results was also made to clarify the fundamental aspects of radiation induced defects in graphite.
