Formation and Annealing of Kr Precipitates in Ni Thin Films

Abstract

Precipitation of Kr implanted into Ni at temperatures between 25 and 560°C, and the annealing behavior up to 600°C of Kr precipitates produced at room temperature have been studied with TEM. At implantation temperatures below about 300°C, Kr precipitation is driven by stochastic (non-diffusional) processes, and the precipitate size-distribution is monomodal. Precipitates with radii less than about 30Å are solid Kr while larger precipitates are in the liquid or gas state. The crystal axis of the solid precipitates are aligned with the axis of the Ni. At higher implantation temperatures, the size-distribution evolves with dose from monomodal to bimodal. The small precipitates are solid Kr while large precipitates are faceted and nonsolid. The average Kr lattice parameter increases with increases in average precipitate size produced by either increasing Kr concentration or implantation temperature. During annealing of room temperature implanted Ni, little growth occurs until temperatures at which solid Kr melts. After Kr melting, precipitates become mobile leading to coalescence and rapid growth. Growth towards an equilibrium shape after coalescence frequently results in additional coalescence and catastrophic swelling. Rate theory modelling of both precipitation and annealing has suggested that solid Kr inhibits precipitate motion, and that Kr melting during implantation or thermal annealing is a precursor to rapid growth by coalescence due to precipitate migration.

Work supported by the U S Dept. of Energy, BES-Materials Sciences, under Contract W-3 l-109-Eng-38.