Extrinsic stress induced defects in CVD diamond

A correlation between the generation of extrinsic defects and the stress produced by the thermal expansion coefficient mismatch between CVD polycrystalline diamond films and the substrate material is established. For this, different ceramic substrate compositions with distinct thermal expansion coefficients were chosen in order to provoke diverse extrinsic stress generation. Diamond films were grown by Microwave Plasma Chemical Vapour Deposition (MPCVD) and all the parameters that cause intrinsic stress, as temperature, gas composition, pressure and deposition time, have been fixed to avoid their effect. It was found that defect-free diamond grains are associated with low stressed coatings, while the highly stressed ones contain multiple narrow twins.