DEUTERIUM RETENTION IN BERYLLIUM AND BERYLLIUM OXIDE

摘要

Retention of deuterium in Be sample and BeO film implanted with D ions or exposed to D atoms at temperatures in the range 300 to 700 K have been studied using SIMS and RGA (residual gas analysis) measurements in the course of surface sputtering. The microstructure of implanted specimens was investigated by TEM. (1) Be and BeO implanted with (3-9) keV D-ions accumulate deuterium in the form of both D atoms and D_2 molecules. In Be irradiated with D ions up to high fluences at which maximum D concentration is reached, the fraction of deuterium trapped in the form of D2 molecules is approx 0.8 at irradiation temperature Tirr =300 K and approx 0 6 at Tirr =700 K. As for BeO, the majority of implanted deuterium is retained as D atoms both at 300 and 700 K. In Be sample and BeO film implanted with D ions at T_irr ?300 K, the D_2 molecules are present in tiny bubbles (Be and BeO) and in intercrystalline non-interconnected gaps (BeO) In Be irradiated 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. The microstructure of BeO film subjected to D ion implantation at Tirr = 700 K is indistinguishable from that of BeO film irradiated at T_irr = 300 K. The high concentration of D atoms in the ion stopping zone of Be matrix and BeO film after implantation to saturated fluences at 7_irr = 300 and 700 K is attributed to deuterium (i) trapped in radiation vacancies, (ii) adsorbed on the walls of bubbles and channels and (iii) chemically bonded to O atoms adjacent to point defects in the BeO lattice. (2) Due to the presence of oxygen containing molecules as trace impurities, the beryllium oxide layer is formed on the surface of Be sample exposed to D atoms at elevated temperatures. It has been found mat the deuterium atom exposure leads to the deuterium retention in tins layer. The majority of deuterium (> 90 percent) retains as D atoms, the other part is accumulated in the form of D_2 molecules. After termination of D atom exposure D concentration in BeO layer decreases with time at room temperature. It is supposed that the formation of beryllium hydroxide Be(OD)_2 under D atoms exposure of growing BeO layer takes place. The decrease of deuterium concentration in time is explained by dehydration of Be(OD)_2.