Diamond nucleation and adhesion on sintered nitride ceramics

AlN, Si3N4 and SiAlON ceramic materials were sintered from sub-micrometre powders, by a hot pressing (HP) or pressureless sintering (PLS) procedures, at temperatures in the range of 1700-1850 degreesC. On these substrates, diamond coatings of different thickness were grown from a CH4/H-2 gas mixture, using a HF-CVD apparatus at 30 torr, 750 degreesC. Different pre-treatments of substrates, including chemical etching, diamond polishing and carbon seeding by pulsed laser deposition (PLD) of a graphite target, were used to study and enhance the first stages of diamond nucleation and growth. The structure and morphology of nitride ceramic substrates and diamond deposits have been characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Diamond film quality and residual stress have been studied by Raman spectroscopy. The polycrystalline film adhesion on the various pre-treated ceramic nitride substrates has been evaluated by the indentation technique (Vickers' indenter). Morphological and structural configuration of polycrystalline diamond/ sintered ceramic nitride interfaces have been studied by SEM cross-sections.