Local structures and damage processes of electron irradiated α-SiC studied with transmission electron microscopy and electron energy-loss spectroscopy

Damaged structures of alpha-SiC below and above the critical temperature of amorphization (T-c) under high-energy electron irradiation were studied by means of transmission electron microscopy and electron energy-loss spectroscopy. Above T-c, crystal fragmentation takes place due to local lattice strains caused by preferential displacements, subsequent outward diffusion of carbon atoms and formation of silicon nano-clusters. On the other hand, the amorphous structure formed below T-c can be well characterized by the formation of Si-Si, Si-C, and sp(3) C-C covalent bonds with the tetrahedral coordination locally retained and uniformly distributed. The primary amorphization process under electron irradiation can be interpreted by the defect-accumulation model, in which displaced atoms are frozen at interstitial sites before long-distance diffusion by reconstructing the surrounding structure to relax the local strains. Accordingly the amorphization process is controlled essentially by the mobility of displaced carbon and silicon atoms, and chemical disordering seems to play a minor role in triggering the amorphization. A key issue for irradiation induced volume swelling of amorphous SiC is also presented. (C) 2003 American Institute of Physics.