The ever more demanding application conditions call for new systems with properties over-performing current material systems. In addition to alloying and self-organisation, multilayer architecture is a perspective concept to reach these goals. For example, it has been shown that TiN/VN superlattices with bi-layer period in a range of several nanometers yield hardness values higher that either of the constituent materials.
We report on first-principles study of uniaxial strength for brittle cleavage of AlN/VN, AlN/TiN and VN/TiN systems. In agreement with a previous report we predict VN/TiN exhibit interface induced toughening of VN as compared to bulk values, and a similar effect is predicted also to occur in the VN/AlN system. However, a more detailed insight reveals, that the theoretical critical stress for brittle cleavage largely oscillates (to values even lower than the bulk critical stress!) with the distance from the interface inside the VN layer, a behaviour not present (or hugely reduced) in TiN and AlN layers. We have been able to correlate this behaviour with oscillating interplanar distances and charge density. We will attempt to provide an explanation for this phenomenon, and will discuss consequences for materials design.