Dielectric and EPR investigations of stoichiometry and interface effects in silicon carbide nanoparticles

The dielectric properties of non-stoichiometric silicon carbide nanoparticles (np-SiC), with a silicon-rich composition in the atomic ratio C/Si = 0.85, are investigated in a wide frequency and temperature range. Two samples, namely S 1400 and S 1700, obtained from the same synthesis batch but submitted to annealing at, respectively, 1400 and 1700 degrees C, are representative of this class of material. In particular, quasi-insulating and semiconducting states are evidenced in these samples, and they point out the influence of the annealing treatment. The dielectric spectra of S 1400 are marked by a relaxation process and by a thermally activated conductivity, whereas only a large dc-conductivity is found in the S 1700 sample. The temperature dependence of both relaxation times and dc-conductivity are determined and interpreted taking into account the transport process in these media. EPR investigations are carried out to correlate the electrical and dielectric behaviour with the surface states of the nanoparticles which exhibit heterogeneous composition and surface active electronic centres. The experimental conductivity and dielectric functions in these silicon-rich materials are discussed and compared with those from carbon-rich np-SiC samples.