Influence of SiC particle addition on the nucleation density and adhesion strength of MPCVD diamond coatings on S3N4 substrates

It is generally accepted that SiC layers are often involved in the adhesion efficiency of chemical vapour deposition (CVD) diamond films on Si-contain ing substrates. Si3N4-SiC composite substrates with different amounts of Si C particles (0-50 wt%) were then used for diamond deposition. Samples were produced by pressureless sintering (1750 degrees C, N-2 atmosphere, 2-4 h). The diamond films were grown on a commercial MPCVD reactor using H-2/CH4 m ixtures. Despite there being no special substrate pre-treatment, the films were densely nucleated when SiC was added (N-d approximate to 1 x 10(10) cm (-2)) with primary nanosized (similar to 100 nm) particles, followed by a l ess dense (N-d approximate to 1 x 10(6) cm(-2)) secondary nucleation. Inden tation experiments with a Brale tip of up to 588 N applied load corroborate d the benefit of SiC inclusion for a strong adhesion. The low thermal expan sion coefficient mismatch between Si,N, and diamond resulted in very low co mpressive stresses in the film, as proved by micro-Raman spectroscopy. (C) 2000 Elsevier Science S.A. All rights reserved.