H dissolution and desorption in W (1 1 0) surface with the presence of He: A first-principles study

Experiments shew that the presence of helium (He) can suppress total hydrogen (H) retention/penetration and surface blistering, while increase tungsten (W) surface H retention. It is thus necessary to reveal the micro-mechanisms of the dissolution and desorption of H in the W surface with the presence of He to understand these two opposite phenomena systematically. It has already known that a surface tungsten vacancy (V) is easier to form than in the bulk and has a large trapping effect on H dissolving. So, the first-principles method is employed to study the effect of the single-vacancy and He-vacancy (HeV) complex on the dissolution and desorption behaviors of H in the W (1 1 0) surface. We found that there are more H capture sites around HeV complex than that around V, which should response for the increase of H retention near surface. In addition, both the trapping energies and desorption barriers of H around HeV complex are lower comparing to those around V, which makes it easier for H to desorb with the presence of He. Therefore, under the irradiation of low-energy plasma, the pre-exposure of He can increase both the trapping sites and desorption rate of H in W surface, which would suppress H penetration into bulk as well as surface blistering.