High-temperature stability of epitaxial, non-isostructural Mo/NbN superlattices

The effect of 1000 degrees C vacuum annealing on the structure and hardness of epitaxial Mo/NbN superlattice thin films was studied. The intensity of superlattice satellite peaks, measured by x-ray diffraction, decreased during annealing while new peaks corresponding to a MoNbN ternary phase appeared. The results are consistent with the Mo-Nb-N phase diagram, which shows no mutual solubility between Mo, NbN, and MoNbN. Even after 3-h anneals and a loss of most of the superlattice peak intensity, the room-temperature hardness was the same as for as-deposited superlattices, The retained hardness suggests that a residual nanocomposite structure is retained even after the formation of the ternary structure.