Growth of nanocrystalline diamond protective coatings on quartz glass

Transparent diamond films with a crystallite size well controlled below 70 nm were grown by hydrogen and methane microwave plasma-enhanced chemical vapor deposition on quartz glass substrates, which had been scratched with 0.5 μm diamond powder. A complementary set of analyzing tools was employed to study the microstructure, the optical and mechanical properties of the deposits. Transmission electron microscopy revealed a nucleation density generally larger than 1011/cm2, which is of the same order of magnitude as the spotlike defects on the pretreated surface of the substrates. The Vicker’s hardness of the deposits scatters between 61 and 95 GPa. An optimal transmittance of 65% in the visible light range is achieved in coatings of 1.0 μm in thickness when the surface roughness measures about 10 nm or less. The nanocrystalline diamond films thus prepared can meet the requirements on transparent protective coatings for optical components.