Helium pre-implantation and post-implantation effects on hydrogen isotope retention in SiC

Helium pre-implantation and post-implantation effects on hydrogen isotope behavior in SiC have been studied by means of X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). It was found that the energetic D₂ ⁺ is trapped by SiC with forming Si-D and C-D bonds. By He⁺ pre-implantation, some D trapping site, namely carbon vacancies, would be largely influenced. He⁺ would be retained in SiC with forming He⁺ blister or remained in the interstitial site. Energetic D2⁺ and He⁺ would also interact with the SiC structure and the damaged structures would be introduced by He⁺ implantation. It was also found that D retention was largely decreased by He⁺ implantation, especially He⁺ post-implantation, indicating the direct interaction between energetic helium and trapped deuterium would be important. The XPS analyses indicated that the free carbon was formed in SiC by ion implantation. Most of free carbon would be recovered by the desorption of D by heating. However, some of C would be migrated toward the surface and aggregated on the surface of SiC. This would cause high tritium retention in fusion reactor.