Interferometric Determination of Twist and Polytype in Silicon Carbide Whiskers

Abstract

Whiskers of hexagonal SiC have been prepared in a graphite tube furnace. They are grown by sublimation of SiC in hydrogen, depositing at temperatures about 2000°C as acicular crystals of hexagonal section, with [0001] along the whisker length. The {11̄00} faces have been examined using optical interference techniques, and are found to exhibit a twist. The Eshelby formula for twist caused by a screw dislocation has been used to estimate the strength of the associated Burgers vector. It is found that, within the experimental error, the estimated Burgers vector is equal to, or is an integral multiple of the unit cell of the SiC polytype 4H. It is thus concluded that these twisted whiskers grow by means of a screw dislocation of integral strength parallel to the axis, and that they are of polytype 4H.