Dielectric properties of nano Si/C/N composite powder and nano SiC powder at high frequencies

The dielectric properties of nano Si/C/N composite powder and nano SiC powder at high frequencies have been studied. The nano Si/C/N composite powder and nano SiC powder were synthesized from hexamethyldisilazane ((Me3Si)(2)NH) (Me:CH3) and SiH4-C2H2, respectively, by a laser-induced gas-phase reaction. The complex permittivities of the nano Si/C/N composite powder and nano SiC powder were measured at a frequency range of 8.2-12.4 GHz. The real part (epsilon') and imaginary part (epsilon'') of the complex permittivity, and dissipation factor (tg delta = epsilon''/epsilon') of nano Si/C/N composite powder are much higher than those of nano SiC powder and bulk SiC, Si3N4, SiO2, and Si, especially the tg delta. The promising features of nano Si/C/N composite powder would be due to more complicated Si, C, and N atomic chemical environment than in a mixture of pure SiC and Si3N4 phase. The charged defects and quasi-free electrons moved in response to the electric field, diffusion or polarization current resulted from the field propagation. Because there exists graphite in the nano Si/C/N composite powder, some charge carries are related to the sp(3) dangling bonds (of silicon and carbon) and unsaturated sp(2) carbons. The high epsilon'' and tg delta of nano Si/C/N composite powder were due to the dielectric relaxation. The nano Si/C/N composite powder would be a good candidate for electromagnetic interface shielding material. (C) 2001 Elsevier Science B.V. All rights reserved.