TEM study of silicon carbide whisker microstructures

Abstract

Β-SiC whiskers produced by a number of manufacturers have been examined in the transmission and scanning electron microscopes. In all cases defective microstructures were found with high densities of planar defects such as stacking faults and microtwins. Two distinct types of defective whisker can be identified. The first contains regions of very closely spaced twins on {111} planes arranged perpendicular to the whisker axis [111], these were sometimes separated by defect-free regions. In these whiskers a rough surface profile was normal with the roughness closely associated with the highly defective regions of the whisker. The second type of whisker contained stacking faults spaced relatively widely also on {111} planes but now on the planes inclined to the [111] axis of the whisker. This leads to a characteristic chevron contrast in the TEM. This second type of whisker had a much smoother surface profile than the first type with perpendicular defects. No whisker contained both defect types but some batches of whiskers contained populations of both types of whisker. The first type of whisker is shown to have defects similar to those reported as common during vapour-liquid-solid whisker growth. This is also consistent with the higher impurity content and the presence of voids found in these whiskers. The second type may be indicative of a different growth mechanism possible under certain conditions of SiC whisker synthesis.