ON THE GROWTH-MECHANISM OF SILICON-CARBIDE WHISKERS

The microstructure of SiC whiskers has been studied through analytical electron microscopy. The whiskers were found to contain discrete regions of high and low planar defect density. These regions of low defect density were identified as 3C beta-SiC, whereas the regions of high defect density were consistent with a mixture of SiC polytypes, with the 3C and the 6H polytypes being the most predominant as a result of the formation of a high density of microtwins on the (111) planes perpendicular to the growth direction. A growth mechanism is suggested based on observations of (a) outer layers of SiC on vapour-liquid-solid catalysts and (b) C:Si variations between the regions of high and low densities of planar defects. It appears that there is some degree of stoichiometric control over the microstructure of the SiC whiskers in that slight carbon enrichments seem to promote the growth of relatively defect-free regions of beta-SiC whiskers.