Doping of helium at Fe/W interfaces from first principles calculation

First principles calculation reveals that helium (He) atoms are energetically unfavorable with big and positive solution energies at various interstitial and substitutional sites of Fe/W interface, which is fundamentally due to the intrinsically repulsive nature of W-He and Fe-He bonds with positive bond energies. Calculation also shows that He atoms in the W lattice should have a tendency to diffuse into the Fe lattice of Fe/W interface, and that He energetically prefers the substitution of W or Fe atom, rather than the interstitial sites. In addition, it is found that the location of He has an important effect on cohesion properties of Fe/W interface, and that He at the very interface area could significantly reduce interface strength and stability of Fe/W. The derived results are not only discussed in terms of electronic structures and bond features to provide a deep understanding, but also in good agreement with experimental observations in the literature.