Structure and mechanical properties of δ-NbN/SiNx and δ′-NbN/SiNx nano-multilayer films deposited by reactive magnetron sputtering

We deposit cubic δ-NbN/SiNx and hexagonal δ′-NbN/SiNx nano-multilayer films using reactive magnetron sputtering in discharge of a mixture of Ar and N2 gas, and explore the effects of SiNx layer thickness on the microstructure and mechanical properties for both cubic δ-NbN/SiNx and hexagonal δ′-NbN/SiNx multilayer films by virtue of X-ray diffraction, electron diffraction, high-resolution transmission electron microscope, and nanoindentation measurements. We find that the structure for NbN layers is a critical factor in determining the hardness of NbN/SiNx multilayer films. For cubic δ-NbN/SiNx nano-multilayer films, as SiNx layer thickness is smaller than or equal to 0.4 nm, the cubic δ-NbN layers force SiNx layers to crystallize, accompanied with a remarkable increase in hardness with maximum hardness of 32 GPa. With an increase in thickness, SiNx layers become amorphous, and correspondingly the hardness decreases. For hexagonal δ′-NbN/SiNx nano-multilayer films, both the stress and hardness decrease with increasing the SiNx layer thickness and the nano-multilayer films do not show any enhancement in hardness, compared to δ′-NbN single layer film.