In-situ transmission electron microscopy study of ion-irradiated copper:: temperature dependence of defect yield and cascade collapse

High-energy neutrons and ions incident upon a solid can initiate displacement collision cascades of lattice atoms which result in localized volumes within the solid that contain high concentrations of interstitial and vacancy point defects. At sufficiently high point-defect concentrations, cascade regions are unstable; recombination of interstitial and vacancy point defects can occur together with the aggregation of point defects into clusters. These clusters can collapse into various types of dislocation loop and stacking-fault tetrahedra which are large enough to produce lattice strain fields that are visible under diffraction-contrast imaging in a transmission electron microscope. The kinetics which drive cascade formation and subsequent collapse are investigated by analysing the microstructure produced in situ by low-fluence 100 keV Kr-ion irradiations of fee Cu over a wide temperature range (18-873 K). The product microstructures are characterized by quantitative measurements of the yields of collapsed point-defect clusters. In addition, their stabilities, lifetimes and size distributions are also examined. Defect yields are demonstrated unequivocally to be temperature dependent, remaining approximately constant up to lattice temperatures of 573 K and then abruptly decreasing with increasing temperature. This drop in yield is not caused by defect loss during or following ion irradiation. It rather reflects a decrease in the probability of cascade collapse which can be explained by a thermal spike effect.