Site preference and diffusion behaviors of H influenced by the implanted-He in 3C-\b{eta} SiC

SiC materials are potential plasma facing materials in fusion reactors. In this study, site preference and diffusion behaviors of H in pure 3C-\b{eta} SiC and in He-implanted 3C-\b{eta} SiC are investigated, on the basis of the first-principles calculations. We find that the most stable sites for H in pure 3C-\b{eta}SiC is the anti-bond site of C (ABc) in Si-C, while it becomes the bond-center (BC) site of Si-C bonds in the He-implanted 3C-\b{eta} SiC. Analysis on the electronic structures reveals that such change is attributed to the reduction of hybridization of C-Si bonds induced by He. Moreover, the presence of He strongly affect the vibrational features in the high frequency region, causing a blue shift of 25 cm-1 for C-H stretch mode with H at ABc site and a red shift of 165cm-1 for that at BC site, with respect to that in the pure system. In pure 3C-\b{eta} SiC, H is diffusive with an energy cost of about 0.5 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 He-implanted 3C-\b{eta} SiC, the energy barriers for H migration goes up to be about 0.95 eV, indicating the implanted-He blocks the diffusive H to some extent. Our calculations also show that the influence of He on H diffusion is effective in a short range, just covering the nearest neighbor.