Evolution of helium platelets and associated dislocation loops in α-SiC

implantation of 2450 at. ppm helium into silicon carbide at room temperature results in the formation of helium platelets with surprisingly uniform diameters about 9 nm, remaining constant upon annealing up to 1270 K. Estimation of the pressure in the platelets suggests the presence of solid helium even above ambient temperature. The narrow size distribution and the limitation of growth of the platelets is attributed to their trapping by circular dislocation dipoles forming close to their rim when they reach a critical size. Upon annealing to approximate to 1500 K, the platelets disintegrate into disks of bubbles and, attached to them, interstitial-type dislocation loops appear. The total volumes of bubble and loop components in such complexes are found to be equal. This striking relation is attributed to the transfer of matrix atoms from the bubbles to the associated loops by dislocation core diffusion. [S0031-9007(99)08776-1].