Electron microscope study of radiation damage in graphite produced by D + and He + bombardment

Abstract

Cleaved highly oriented pyrolytic graphite was irradiated at temperatures between 100 and 700°C, with D + and He + ions with the acceleration voltage of 25 keV and the doses up to 3.0 × 10 18 ions/cm 2 , and examined by transmission electron microscopy. The graphite irradiated by either D + or He + ions is amorphized at a critical dose, which is monitored by the structureless electron image and the appearance of a halo in the diffraction pattern. The critical dose increases with the irradiation temperature and even the irradiation at high temperature as 500°C gives the amorphization. Though the critical dose for D + irradiation is higher than for He + irradiation, the critical dpa calculated from the energy deposition agrees well between the two cases. Therefore it seems that the amorphization of graphite by energetic ion bombardment is mainly controlled by the energy deposition and the difference in chemical nature of the incident particles plays a minor role. The macroscopic defect structures which appeared after the amorphization are, however, somewhat different between the two cases.