  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.
