Low-temperature release of ion-implanted helium from nickel

This letter presents data on the release of He from Ni at temperatures between 18 and 300 K after ion implantation of He at 18 K. The release occurred in two stages, a sharply peaked release near 50 K and a broad release that extended from 80 to 300 K. For He doses in the range of 5 x 1014--1.4 x 1016 cm-2 and shallow implantation depths (<1000 A) the fraction released was 1.5% in the first stage and 4% in the second. For a dose of 4.4 x 1016 cm-2, the fraction released in the first stage was significantly higher. The activation energy for the first stage release was 0.11 +- 0.02 eV for all doses