Effects of the Layered Graphite Structure at High Fluences of 30 keV Helium Ion Irradiation

The effect of high-fluence 30 keV helium ion irradiation with the fluence from 10¹⁸ to 3 × 10¹⁸ cm^–2 in the temperature range from room temperature to 600°C on the morphology and surface structure of highly oriented pyrolytic graphite UPV-1T and fine-grained polycrystalline graphite MPG-8 has been studied experimentally. Ion-induced morphological elements complementing those previously established at low irradiation fluences (~10¹⁷ cm^–2) have been identified. Irradiation of highly oriented pyrolytic graphite at high fluences results in delaminations, which manifest themselves as graphite flakes that are bent, twisted, and have whisker-like structures. Irradiation of fine-grained graphite does not significantly change its microstructure compared to highly oriented pyrolytic graphite.