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

Abstract 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 Si C at the side of C (ABc), while it becomes the bond-center (BC) site of Si C in the He-implanted 3C-β SiC. Analysis on the electronic structures reveals that such change is attributed to the reduction of hybridization of C Si 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 C H 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 Si C 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.