Two-phase nanostructured carbon nitride films prepared by direct current magnetron sputtering and thermal annealing

Two-phase nanocrystalline/amorphous carbon nitride films have been successfully prepared by direct current magnetron sputtering and the following thermal annealing at 1000 K. The analysis of Raman spectra supports the existence of sp3-hybridized C–N bonds in the films. The results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the fractional concentration of the tetrahedral bonded crystalline phase in the carbon nitride films is 40%, and the ratio of N:C in the tetrahedral bonded crystalline phase is 1.12:1. Transmission electron microscopy (TEM) investigations indicate that the films contain a very dense and homogenous distribution of nanocrystalline grains, and the lattice parameters of these crystalline phases are in good agreement with the theoretically predicted β-C3N4 lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the correlations between the microstructure of the films and their mechanical properties are discussed.