INORGANIC FIBERS AND MICROSTRUCTURES DIRECTLY FROM THE VAPOR-PHASE

By using high reactor pressures (> 1 bar) and a unique rate control mechanism, chemically pure and structurally uniform boron, carbon, silicon, silicon nitride and silicon carbide fibers were obtained by laser-assisted chemical vapor deposition (LCVD) with high growth rates (0.3-1.1 mm/s), high tensile strengths (up to 7.0 GPa) and small diameters (>9 mum). The boron, carbon and silicon nitride fibers were amorphous, the silicon carbide fibers polycrystalline, and the silicon fibers either glassy, polycrystalline or single crystals. The latter were formed by a vapor-liquid-solid (VLS) mechanism. The process speeds, and most likely the first-order process economics, are about the same as those reported for the commercial manufacture of single crystal sapphire fibers (which are, however, made by a different process). A commercial LCVD multifilament process is being developed. LCVD was also used to grow free-standing, three-dimensional microstructures (grids, springs, solenoids) directly from the vapor phase. Related microstructures (microwafers with VLS silicon bristles) are also becoming commercially available.