Evolution of Kr Precipitates in Kr-Implanted Al as Observed by the Channelling Method

The evolution of Kr precipitates at room temperature from nucleation to the formation of solid Kr precipitates in Al implanted with 50 keV Kr+ ions has been studied through the site change of Kr atoms determined by the channelling method. A previous channelling study reported that nucleation centres are various types of Kr-vacancy (V) complexes formed at low implantation doses. In this study, the initial stage of growth of Kr precipitates to bubbles and a key process towards the formation of epitaxially aligned solid Kr precipitates are investigated. The growth of Kr precipitates to bubbles proceeds from the accumulation of Kr atoms migrating to Kr-V complexes by radiation-enhanced diffusion. The Kr bubbles are in the fluid state. As to the epitaxial alignment, the following mechanism is proposed. At implantation doses higher than 2 x 10^sup 15^ Kr/cm^sup 2^, small clusters of Kr atoms located at octahedral (O) or displaced O sites are formed on the planes parallel to ...111... planes at the bubble-matrix interface at the ...111... facets of bubbles. They act as a trigger for epitaxial alignment. (ProQuest: ... denotes formulae/symbols omitted.)