In-situ observation of the dynamic behavior of cascade defect clusters formed by irradiation with high-energy self-ions at 50 K in Cu

We have observed the development of cascade defects formed by irradiation with 400 keV Cu+ ions in high-purity Cu at 50 K, and demonstrated the one-dimensional motion of freely or sporadically migrating small defect clusters during post annealing, using in-situ electron microscopy. The diffusivity for the back-and-forth one-dimensional motion of the freely migrating clusters during the post annealing at 50 K was evaluated based on the random walk theory. The free migration distance during the sporadic 1-D motion of the small clusters decreased with increasing the fluence of irradiated ions, which suggests trapping sites of radiation-induced defects. A significant number of cascade induced defects changed their positions and shapes at 50 K, and were annihilated by post annealing at 100 or 150 K. The present results for the free or sporadic 1-D motion of small defect clusters have a great impact on the current understanding of defect recoveries in stages ID+E and II for fcc metals.