Impurity effects and temperature dependence of D retention in single crystal tungsten

Deuterium retention in single crystal tungsten was measured as a function of implantation temperature (300–700 K), fluence (1021–1025 D+/m2 s) and impurity levels for 500 eV/D+ implantation. Prior to implantation, specimens were annealed under vacuum at temperatures up to 2200 K with the intention of reducing the impurity and defect contents. Secondary ion mass spectrometry measurements showed that near-surface carbon and oxygen levels decreased after annealing at 1775 K, but increased after annealing at 2200 K, and also increased after D+ implantation. Thermal desorption spectra indicated that D retention increased with increasing D+ fluence (with an apparent trend to saturation for implantation at 300 K), and decreased with increasing implant temperature. The desorption peaked at T=600–900 K, depending on the implant fluence and temperature. There was little or no D retention for implantation at T>700 K. C and O impurities are affected by the D+ irradiation and appear to influence the D trapping mechanism and the amount of D retained.