IR transmittance of large-sized free-standing transparent diamond films prepared by MWPCVD

Large-sized free-standing transparent diamond films of 50 mm diameter and 300 μm thickness were prepared by microwave plasma chemical vapor deposition (MWPCVD). The growth rate of the diamond film was only 1–2 μm/h when the diamond film was grown at a methane concentration of 2%, and the infrared (IR) transmittance reached 70% in the range of 500–4000cm−1 after the film was polished on both sides. A high growth rate of 7–8 μm/h was achieved for the film grown at a methane concentration of 4%. The thickness of the film was 260 μm after it was polished on both sides and its IR transmittance in the range of 500–4000 cm−1 reached about 60%. Meanwhile, the IR transmittance was almost the same in the central and fringe regions. These results imply a promising application of large-sized thick diamond films in IR windows.