Nanocrystalline diamond thin films as infrared optical protective coatings

Nanocrystalline diamond thin films have been grown on both sides of Si wafer by microwave plasma-enhanced chemical vapor deposition using a mixture of CH₄ and H₂ as source gas. It was shown that infrared transmission of Si has been greatly enhanced and the maximum transmittance reaches 85%. By optimizing the film thickness, we can obtain the maximum increment in the desired infrared wavelength range. Sand spraying test showed that, while the bare Si substrate exhibited obvious surface damage, no damage could be observed on the diamond surface after the sand spraying. The results confirm that the nanocrystalline diamond films coated on Si can not only increase the infrared transmission but also act as a protective coating.