Fabrication, microstructure and optical properties of 〈110〉 textured CVD polycrystalline diamond infrared materials

The fabrication of "bulk" diamond materials with high transmittance and enough thickness was essential for application as infrared windows. The present work reported the preparation, microstructure and optical properties of polycrystalline diamond materials by MPCVD method using ultralow nitrogen doping (0–80 ppm). The effects of nitrogen concentration and synthesis temperature on the crystalline quality, microstructure, and infrared transmittance were systematically studied by XRD/Raman, SEM/TEM, and UV–VIS/FTIR spectrophotometer, respectively. The results showed that nitrogen doping with appropriate concentration could promote the formation of texture with strong <110> plane orientation, and the growth rate was significantly enhanced without obvious reduction in the optical quality. The freestanding diamond materials fabricated at the nitrogen concentration (10–20 ppm) had high <110> texture degree, enough thickness (>0.7 mm), fast growth rates (~3–6 μm/h), and peak transmittance of ~70.1 % in the infrared band (3.0–15.0 μm). The nitrogen doped diamonds fabricated by this process had excellent performance which showing potential applications as infrared windows for ultrahigh-speed aircrafts.