Significant impact of individual surface and modulation structure on mechanical properties of NbN/NbB2 multilayers

Abstract The controllable growth of NbN/NbB 2 multilayers at a constant modulation period of 10 nm with different modulation ratios (t NbN : t NbB2 ) was achieved through magnetron sputtering system. The X-ray diffraction (XRD) and X-ray reflectivity (XRR), cross-sectional transmission electron microscopy (TEM) and scanning electron microscopy (SEM) examinations indicated that in the alternately deposited monolayers of NbN and NbB 2 , a clear multilayer structure was obtained and the diffraction peaks were assigned to typical cubic structure of NbN and hexagonal structure of NbB 2 . For the cubic NbN, the combination of surface energy and strain energy affected NbN (111) and (200) texture in polycrystalline NbN layers. Moreover, the multilayers appeared a superhard effect due to mainly the preferential growth of NbB 2 (001). The corresponding highest hardness and critical load reached 36.86 GPa and 87.93 mN, respectively, at a t NbN : t NbB2 of 1:4. The preferential growth of NbB 2 (001) texture was investigated by first-principle. Through CESTEP calculation of the NbB 2 (001) and (101) surface, the main texture of bulk NbB 2 , the (001)-B surface is the most stable surface. The calculated results revealed the nature of the preferential growth in NbN/NbB 2 multilayers, which offered a profound understanding of its growth mechanism.