Cryotransfer transmission electron microscopy experiment of low-temperature 14 MeV-neutron irradiated aluminium

Cryotransfer transmission electron microscopy (TEM) was applied to examine the defect structure created by displacement collision cascades in a thin Al foil which was irradiated at 20K with 14MeV neutrons to a dose of 1.8 x 1021 neutrons m-2. No visible defect clusters were found in the as-irradiated specimen or after isochronal anneals to 323K. The results are consistent with a nascent defect structure consisting of submicroscopic interstitial-type clusters, single vacancies and submicroscopic vacancy-type clusters. Subthreshold (100kV) electron illumination, however, induced the formation of TEM visible defect clusters at 150K. 91% of these in the as-irradiated specimen were interstitial-type, and all in the specimen isochronally annealed at 273 K were vacancy-type. The growth of interstitial-type defect clusters is the result of the production of migrating interstitial atoms by the decomposition of submicroscopic interstitial-type clusters, and that of vacancy-type defect clusters is attributed to the electron-radiation-induced diffusion of single vacancies. Comparisons with other cryotransfer TEM experiments are also presented. (author)