Preparation and Microwave Permittivity of Nano Si/C/N Composite Powders Suspended in Different Matrixes

The nano Si/C/N composite powders were synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser-induced gas-phase reaction. The powders are spherical, loosely agglomerate with sizes in range of 20-30nm. The laser synthesis reactor consists of two reaction zones, which can efficiently increase laser efficiency and production yield. The microwave permit- tivities of nano Si/C/N composite powders suspended in different matrixes were studied at the frequency range of 8.2-12.4GHz. The e' and e of the nano Si/C/N composite powder decrease with frequency at the frequency range of 8.2-12.4GHz. The difference being the microwave reso- nance is not sharply peaked but rather smeared out over a large frequency range. The dissipation factors tgδ(e/e') of the nano Si/C/N composite powders are high at the microwave frequencies. The SiC microcrystallines in the nano composite powders can dissolve a great deal of nitrogen, so charged defects and quasi-free electrons move in response to the electric field, diffusion or polarization current resulted from the field propagation. The high e and tgδ of nano Si/C/N composite powders are due to the dielectric relaxation. The unusual e',e and tgδ of the nano Si/C/N composite powders suspended in different matrixes are attributed to the interface effects between nano Si/C/N composite powders and matrixes.