Erosion damage and optical transmittance of diamond films

Diamond films on silicon wafers were fabricated by microwave chemical vapor deposition to investigate the effect of erosion damage on optical transmittance. After deposition, the growth side was mechanically polished and the silicon substrate was removed by chemical etching with hydrofluoric acid to make an optically flat infra-red (IR) window. With prolonged erosive impacts by SiC particles, the two sides of free-standing diamond windows showed significantly different damage resistance. The optical transmittance of the substrate side, which has smaller diamond grains, was maintained to be the same as that of the non-eroded diamond even after 400 times of repeated erosive impacts. However, optical transmittance of the nucleation side, which has larger diamond grain, was too low to be used as an IR window. The difference in the damage resistance between the substrate side and growth side is discussed based on scanning electron microscopy of the eroded region to explain the different optical behavior of transmittance.