EVOLUTION OF DEFECT STRUCTURES IN COPPER BY HE-+ ION IRRADIATION UNDER THE CONTROL OF FREE POINT-DEFECTS

The role of free interstitial atoms and the effect of implanted helium were studied by a comparison of the defect structures developed in masked thin foils and in bulk samples of copper by 500 kev He+ ion irradiation at room temperature. A minimum PKA energy of 23 kev for cascade damages to form a SFT has been deduced from an analysis of linear increase of the number of stacking fault tetrahedra (SFT) in thin foils at low fluence. The mechanism of defect saturation in the thin foils at higher fluence is analyzed from the number density of SFT. Point defect clusters in the bulk specimens are more readily annihilated at the depth where little helium is implanted. In contrast, the interstitial cluster formation is enhanced at the depth where helium atoms are deposited. The depth variation of the interstitial type dislocation loops observed in the bulk is understood in terms of the trapping of vacancies and interstitial atoms by the helium atoms.