First-principles investigation of the orientation influenced He dissolution and diffusion behaviors on W surfaces

The dissolution and diffusion behaviors of helium (He) for four low-Miller-index tungsten (W) surfaces [(110), (100), (112), and (111)] are systematically studied using the density functional theory to understand the surface-orientation-dependent He bubble formation. The results show that He accumulation on the surfaces is mainly affected by self-trapping and the formation of He-induced vacancies. He-induced vacancies tend to form on the surfaces of W(111), W(100), and W(112) than in the bulk. Specifically, for the W(111) surface, He accumulation is facilitated by the high activation barrier arising from He-induced vacancy trapping, whereas the W(110) surface is resistant to the formation of He bubbles because of the higher vacancy and He formation energies. Our results are helpful for understanding the orientation dependence of surface damage on the W surface under low-energy high flux He ion irradiation and designing irradiation-resistant plasma-facing materials.