Silicon Carbide Whiskers and the VLS Mechanism
Silicon carbide whiskers can be grown by pyrolysis of silica and cellulose derived from rice hulls. Whiskers grown by this process are useful as composite reinforcements in a wide range of matrix materials. Due to the scarcity of published information regarding the crystal growth mechanism, research was devoted to analysis of inclusions and defects in the whiskers. Most SiC whiskers exhibited microinclusions (<10nm in size) confined to a central core region (Fig. 1). The distribution implies a two-stage growth process in which the core region grows in the first stage, followed by lateral growth in the second stage. An HREM image of a single twinned inclusion is shown in Fig. 2. The whisker orientation is [0001] and the inclusion exhibits crossed 0.45nm lattice fringes running parallel to type II prism planes in the SiC lattice. The lattice fringes often did not span the entire inclusion diameter, and radiation damage to the inclusion was observed with increasing dose using a 200 kV electron beam.