Helium and strontium co-implantation into SiC at room temperature and isochronal annealing : structural evolution of SiC and migration behaviour of strontium

Abstract

Understanding the structural evolution of SiC implanted with fission product surrogates in the presence of helium (He) is of importance for its application in both fission and fusion rectors. In this study, polycrystalline SiC wafers were sequentially co-implanted with 360 keV Sr and 21.5 keV He ions to a fluence of 2 × 1016 cm-2 and 1 × 1017 cm-2 at room temperature, respectively. The samples were then isochronally annealed in temperatures ranging from 1000 to 1300 °C for 5 h. Transmission electron microscopy (TEM) showed the formation of He-nanobubbles corresponding to helium's projected range. While scanning electron microscopy (SEM) revealed the formation of cornflower-like structures on the surface of the Sr + He–SiC samples after annealing. These were confirmed to be holes by atomic force microscopy (AFM), as a result of exfoliation and pressurized out-diffusion of helium gas from the samples. The Sr + He–SiC samples were completely amorphized characterized by the formation of the homonuclear bonds in Raman spectroscopy. The recovery process after annealing in the Sr + He–SiC samples resulted in the formation of graphite due to antisite defects driven by the growth of holes above the threshold chemical disorder. Time-of-flight heavy ions elastic recoil detection analysis (Tof-ERDA) showed that almost all helium out-diffused after annealing at 1000 °C and Sr atoms trapped in He cavities.