Depth distribution of deuterium atoms and molecules in beryllium implanted with D ions

Abstract

In-depth concentration profiles of deuterium atoms and molecules in beryllium implanted with 9 keV D ions to fluences, Φ, in the range from 6 × 10 19 to 9 × 10 22 D/ m 2 at temperatures, T irr , of 300 and 700 K have been determined using SIMS and RGA (residual gas analysis) measurements in the course of surface sputtering. The microstructure of implanted specimens was studied by TEM. Implanted deuterium is retained in Be matrix in the form of both D atoms and D 2 molecules. The total amount of gas captured within the sub-surface layer of ∼ 700 nm in thickness as a result of implantation at 300 and 700 K reaches 4 × 10 21 and 1 × 10 21 D/ m 2, correspondingly. The ratio of deuterium quantities retained in the form of atoms and molecules, Q D : Q D 2 , varies from 1:3 for T irr = 300 K to 1:4 for T irr = 700 K. At T irr = 300 K the concentration of D 2 molecules at the depth of the ion mean range reaches its maximum of 4 × 10 27 molecules/ m 3 at Φ ≈ 2 × 10 21 D/ m 2. The molecules are present in tiny bubbles which show a tendency toward interconnection at higher fluences. At T irr = 700 K, along with relatively small facetted bubbles (near the very surface), large oblate gas-filled cavities and channels forming extended labyrinths appear and they accumulate most of the injected gas. The maximum D 2 concentration in the latter case is of 1 × 10 27 molecules/ m 3. The high concentration of D atoms in the ion stopping zone after implantation at T irr = 300 and 700 K (about 2 × 10 27 and 1 × 10 27 atoms/ m 3, respectively) is attributed to deuterium (i) trapped in radiation vacancies, (ii) adsorbed on the walls of bubbles and channels and (iii) bonded to/by BeO formed on the surface and present in the form of metallurgical inclusions in the bulk.