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

implantation of 2450 at. ppm helium into silicon carbide at room temperatur e results in the formation of helium platelets with surprisingly uniform di ameters about 9 nm, remaining constant upon annealing up to 1270 K. Estimat ion of the pressure in the platelets suggests the presence of solid helium even above ambient temperature. The narrow size distribution and the limita tion 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 i nto disks of bubbles and, attached to them, interstitial-type dislocation l oops appear. The total volumes of bubble and loop components in such comple xes are found to be equal. This striking relation is attributed to the tran sfer of matrix atoms from the bubbles to the associated loops by dislocatio n core diffusion. [S0031-9007(99)08776-1].