| The fabrication of various nanomaterials that possess desirable properties such as high temperature stability, extreme hardness, and corrosion resistance has attracted the interest of various research groups. Among the materials of interest, silicon nitride, and group four diborides are known for exceptional properties including enhancement of the mechanical and thermal properties of composites. Conventionally, these materials have been produced in a traditional chemical vapor deposition (CVD) apparatus that has utilized thermal energy to drive the reactions at very high temperature. At high temperature, the vaporization of liquid or solid precursors alters the pressure inside the CVD reactor as the mass of the precursor held in the sampling boat decreases overtime. This leads to a fluctuation of the precursor concentration in the reagent stream. As the result of these limitations, it is not possible to consistently fabricate nanowires of desired composition. Therefore, in this thesis we designed, constructed and evaluated a microwave plasma enhanced chemical vapor deposition (PECVD) system to alleviate these problems. This has been achieved by carrying out CVD reactions at relatively low temperature since the microwave plasma has created dissociated gaseous molecules, excited state ions, and a mixture of energetic gaseous components that react spontaneously. Fluctuation of the precursor concentration is eliminated by installing a mass and pressure controller in tandem. Using the PECVD system, the fabrication of silicon nitride and zirconium diboride nanowires has been investigated to optimize the processing of scalable quantities of the materials. Known methods with the highest potential for the synthesis of nanowires were investigated. These included direct nitridation of silicon substrates and metal catalyzed etched silicon wafers, thermo-transformation of pre-ceramic polymer, autoclave reactions, and solid state mechanical alloying. Additionally, a novel method was developed based on the catalyzed conversion of silicon nitride nanopowder into nanowires. Similarly, zirconium diboride nanowires (rods) have been synthesized by employing solid state mechanical alloying with subsequent thermo-transformation. Finally, the synthesized nanowires were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray florescence spectroscopy (EDAX). |
