Improving mechanical properties of amorphous carbon nitride films by titanium doping

Titanium doped amorphous carbon nitride (a-CNx) films with a nitrogen content of ∼24at.% were synthesized by radio frequency magnetron sputtering method. The effects of incorporating Ti on the mechanical properties of a-CNx films were investigated by nanoindentation, scanning electron microscope, x-ray diffraction spectra, and x-ray photoelectron spectroscopy, respectively. It was found that nanometer sized TiN crystallites were formed and embedded in the a-CNx matrix, causing an enhancement of hardness from ∼28to∼40GPa in the a-CNx films. The improved mechanical properties with addition of Ti are attributed to the densified microstructure due to the development of fine grain size of TiN and sp3 C–N bonds. These TiN nanocrystal grains are separated by an amorphous phase, preventing dislocation movement and hence enhancing the hardness of the film. The increased sp3 C–N bond fraction induced by incorporation of Ti also plays an important role in the enhancement of hardness.