On the application of the weak-beam technique to the determination of the sizes of small point-defect clusters in ion-irradiated copper

We have made an analysis of the conditions necessary for the successful use of the weak-beam technique for identifying and characterizing small point defect clusters in ion-irradiated copper. The visibility of small defects was found to depend only weakly on the beam convergence. In general, the image sizes of small clusters were found to be most sensitive to the magnitude of s(g), with the image sizes of some individual defects changing by large amounts with changes in s(g) as small as 0.025 nm(-1). The most reliable information on the true defect size is likely to be obtained by taking a series of 5-9 micrographs with a systematic variation of deviation parameter from 0.2-0.3 nm(-1). This procedure allows size information to be obtained down to a resolution limit of about 0.5 nm for defects situated throughout a foil thickness of 60 nm. The technique has been applied to the determination of changes in the sizes of small defects produced by a low-temperature in-situ irradiation and annealing experiment.