The effect of SiC substrate microstructure and impurities on the phase formation in carbide-derived carbon

Carbon layers were obtained by etching of different silicon carbides with Cl₂/H₂ gas mixtures at high temperatures (carbide-derived carbon). The resulting layers were studied by analytical and high resolution transmission electron microscopy. It was found, that etching of high purity single crystal SiC wafers exclusively yields amorphous carbon. The development of graphite-like and nanodiamond inclusions was observed using commercially available sintered SiC and polymer-derived SiC, which both contained boron- and carbon-rich phases. The presence of turbostratic graphite regions and isolated diamond particles in the bulk of non-chlorinated sample was revealed in the commercial polycrystalline SiC substrate. This fact points to the possible nucleation and growth of diamond phases during sintering of the commercial SiC substrate. Chlorination of boron-implanted single crystal SiC wafer showed that the presence of boron-rich dopants in the SiC alone does not trigger the nucleation of diamond phases. An initial surplus of carbon in the SiC substrates appeared to be required as could be shown for boron doped polycarbosilane derived SiC. Thermodynamic considerations assisted by quantum chemical calculations showed the low effect of hydrogen in the Cl₂/H ₂ gas mixtures during SiC chlorination for the nucleation of diamond phases.