Formation and stability of enhanced superhard nanostructured AlN/VN and AlN/TiN superlattice materials

摘要

Using density functional theory and the full-potential linearized augmented plane wave (FLAPW) method, we investigate the formation and stability, and atomic structure, of rock-salt AlN/TiN and AlN/VN systems, including properties of the clean surfaces of the constituent materials. Calculations of the adlayer formation energy highlights the effect and interplay of the various energetic contributions on the growth of these strained systems, where the so-called "surface-interface" interaction energy is found to be important for the initial stages of AlN epitaxy. A significant strain energy builds up for increasing number of layers, where it is greater in the AlN/TiN system, which limits the thickness of rocksalt AlN regions that can grow before a. structural transition to the lower energy wurtzite phase takes place. From our calculations, together with the known experimental critical thicknesses, we can obtain an accurate estimate of the wurtzite/substrate interface energy. That these values are high explains why the metastable rocksalt phase, which has significantly lower interface energies, is stabilized.