Nitrogenated nanocrystalline diamond films: Thermal and optical properties

Ultrananocrystalline diamond films have been grown by microwave plasma CVD using CH4/H2/Ar mixtures with N2 added in plasma in amounts up to 25%. The films were characterized with AFM, Raman, XRD, and UV–IR optical absorption spectroscopy mainly focusing on optical and thermal properties. In comparison with polycrystalline CVD diamond the UNCD are very smooth (Ra < 10 nm), have low thermal conductivity (∼ 0.10 W/cm K), high optical absorption (∼ 103 cm− 1 at 500 nm) and high concentration of bonded hydrogen (∼ 9 at.%). The nitrogen presence in the plasma has a profound impact on UNCD structure and properties, particularly leading to a decrease in resistivity (by 12 orders of magnitude), thermal conductivity, Tauc band gap, optical transmission and H content. The UNCD demonstrated rather good thermal stability in vacuum: the diamond phase still was present in the films subjected to annealing to 1400 °C.