Synthesis and dielectric properties of nano Si/C/N powders

Nano Si/C/N powders with different configurations were prepared by Chemical Vapor Deposition (CVD). The crystallinity of the products increased with increasing reaction temperature. The powder prepared at 1200°C consisted of amorphous spherical particles with a particle size of 20 to 50 nm. The nanocrystalline particles produced at 1400°C, with a mean size from 50 to 100 nm, were also spherical. The powder prepared at 1600°C consisted of whiskers with a diameter from 20 to 50 nm, and the length ranged from 100 to 200 μm. XRD results indicated the whisker sample was mainly β-SiC, which was in good agreement with the SAED pattern. The permittivity of the powders was measured in the frequency range from 8.2 GHz to 12.4 GHz and loss tangents were calculated also. The permittivity and loss tangent of the amorphous Si/C/N nano powder were the lowest of the three samples studied. The ε′, ε″ and tanδ of the Si/C/N powders all decreased with increasing frequency. Impurity conduction, charged defects, quasi-free electrons, and π-bonds caused by nitrogen dissolved in the SiC lattice were the reasons for the dielectric loss of the Si/C/N powders.