The study of heavy-ion damage in pure copper

Abstract

TEM has been used to study the small vacancy clusters (8 Å ≤ diameter ≤ 90 Å) created in pure copper by 30 keV ions. Quantitative investigations show that cluster visibility depends on the imaging conditions such as the orientation of the foil, the magnitude of the diffraction vector g and the deviation parameter w. The main conclusion is that reliable and accurate determinations of the geometry, density, size and depth distribution of the defect clusters require a combination of micrographs taken under a series of strong-beam diffraction conditions or a combination of strong- and weak-beam conditions. Failure to do this can result in significant errors, particularly in determining the number density where a combination of micrographs is required to identify the layer boundary loops, which represent ≥ 20% of the loop population at any given diffraction condition.

The damage consisted entirely of Frank loops equally distributed on the four {111} planes. The degree of dissociation on neighbouring planes of many of these loops was found to be a function of foil orientation being greater in 〈111〉 than in 〈011〉 foils. A defect yield of 0·50 ± 0·01 was obtained with Cu⁺ ions and 0·60 ± 0·01 with W⁺ ions, whereas the cascade efficiency was 0·35 ± 0·02 with Cu⁺ ions but increased by a factor of two with W⁺ ions owing to the increase in vacancy supersaturation. Larger loops were found on the edge-on than the inclined planes with both types of ions. This is explained in terms of a model which allows more efficient collapse and growth on the edge-on planes because of elongation of the average cascade along the ion beam direction.