Comparison of diamond film adhesion on molybdenum substrates with different surface morphologies

To evaluate the effect of substrate morphology on the adhesion of diamond film, two types of substrate morphology of molybdenum (Mo) were compared. The two morphology types were formed by polishing a Mo substrate with SiC abrasive paper along one direction (anisotropic morphology) and by polishing the Mo substrate with diamond powder in a random direction (isotropic morphology). Ultrasonic cavitation tests were conducted to evaluate the adhesion of the diamond films on these Mo substrates. In the case of low surface roughness, there was very little difference between the effects of SiC abrasive paper polishing and diamond powder polishing. In the case of high surface roughness, the adhesion of the diamond film on the SiC paper polished Mo substrate was larger than that of the diamond film on the diamond powder polished Mo substrate. Detachment of the diamond film from the SiC paper polished Mo substrate progressed along the polishing direction; while detachment of the diamond film from the diamond powder polished Mo substrate progressed in a random direction. It was thought that the detachment of the diamond film from a Mo substrate having an anisotropic polishing trace was suppressed because the anisotropic grooves restricted the formation of connections between the points of detachment at right angles to the groove direction. Therefore, the anisotropic surface morphology of the Mo substrate is effective for improving the adhesion of diamond film.