Deuterium trapping behavior in tungsten surface due to low-energy ion irradiation

Deuterium (D) irradiation at 421–597 K was performed on polycrystalline tungsten with 100 eV D ions up to a fluence of 4.64 × 1023 m−2. A supersaturated layer in the ion stopping range (< 20 nm) with the concentration of 1.2 at.% under the present surface resolution of ∼ 12 nm, a shallow minimum D concentration area of > 100 nm and a subsequent significant increase in the sub-surface were revealed by combining D (12C, D) 12C elastic recoil detection and D (3He, p) 4He nuclear reaction analysis. The first-principle calculations indicated that the trapping of vacancies for hydrogen (H) atoms can greatly reduce the recombination probability of Frenkel pairs and then act to stabilize the Frenkel pair. The stabilizing effect can be enhanced with increasing number of H atoms. Furthermore, the vacancies from Frenkel pairs can trap more surrounding H atoms, resulting in further H enrichment which could account for the formation of supersaturated layers. The typical location of the blister cavities coincides rather well with the subsequent significant increase in the sub-surface area. D-induced damage in the supersaturated layer and the sub-surface layers was examined by combining scanning electron microscope, transmission electron microscope and positron annihilation measurements.