Influence of SiC particle addition on the nucleation density and adhesion strength of MPCVD diamond coatings on Si 3 N 4 substrates

Abstract

Abstract It is generally accepted that SiC layers are often involved in the adhesion efficiency of chemical vapour deposition (CVD) diamond films on Si-containing substrates. Si 3 N 4 –SiC composite substrates with different amounts of SiC particles (0–50 wt%) were then used for diamond deposition. Samples were produced by pressureless sintering (1750°C, N 2 atmosphere, 2–4 h). The diamond films were grown on a commercial MPCVD reactor using H 2 /CH 4 mixtures. Despite there being no special substrate pre-treatment, the films were densely nucleated when SiC was added ( N d ≈1×10 10 cm −2 ) with primary nanosized (∼100 nm) particles, followed by a less dense ( N d ≈1×10 6 cm −2 ) secondary nucleation. Indentation experiments with a Brale tip of up to 588 N applied load corroborated the benefit of SiC inclusion for a strong adhesion. The low thermal expansion coefficient mismatch between Si 3 N 4 and diamond resulted in very low compressive stresses in the film, as proved by micro-Raman spectroscopy.