Fabrication and Characterization of Nanocrystalline Diamond Vacuum Window

The ultrathin nano-crystalline diamond (NCD) vacuum window was fabricated. First, the NCD coating was synthesized on substrate of Si wafer by microwave plasma chemical vapor deposition (MPCVD) in an atmosphere of gas mixture of H₂, CH₄, Ar and a little O₂; next, the 200~300 μm thick microcrystalline diamond (MCD) coating was deposited on the NCD coatings masked with a circular Cu-film, 5 mm in diameter; and finally, a NCD window was fabricated by removing the Si-substrate and Cu-mask. The NCD windows were characterized with scanning electron microscopy, Raman spectroscopy, X-ray diffraction and atomic force microscopy. The results show that the NCD vacuum window meets the stringent requirements. For example, the 20 μm thick NCD window, with mechanically reinforced support of MCD coatings, displays favorable properties, including a surface roughness of 34. 6 nm, an average grain-size of 35 nm and a leakage rate of 2. 78×10^-9 Pa·m³/s.