Site preference and diffusion behaviors of H influenced by the implanted-He in 3C-β SiC

SiC materials are potential plasma facing materials in fusion reactors. In this study, site preference and diffusion behaviors of H in the pure 3C-β SiC and in the He-implanted 3C-β SiC are investigated, on the basis of the first-principles calculations. We find that the most stable sites for H in the pure 3C-β SiC is the anti-bond site of SiC at the side of C (ABc), while it becomes the bond-center (BC) site of SiC in the He-implanted 3C-β SiC. Analysis on the electronic structures reveals that such change is attributed to the reduction of hybridization of CSi bonds induced by the implanted He. Moreover, the presence of He strongly affects the vibration features of the system in the high frequency region, causing a blue shift of 3.10 meV for CH stretch mode with H at ABc site and a red shift of 20.46 meV for that at BC site, with respect to that in the pure system. In the pure 3C-β SiC, H is diffusive with an energy cost of about 0.50 eV, preferring to rotate around the C atom in a SiC tetrahedron with an energy barrier of just about 0.10 eV. In contrast, in the He-implanted 3C-β SiC, the energy barrier for H migration goes up to be about 0.95 eV, indicating that the implanted-He blocks the diffusive H to some extent. Our calculations also show that the influence of He on H diffusion works in a short range, just covering the nearest neighbors.