Thickness-dependent structural transformation in the AlN film

We report the nature of the thickness-dependent structural transformation in AlN film. The non-equilibrium cubic AlN, which normally exists under high pressures of more than 22.9 GPa, can be epitaxially stabilized in ambient atmosphere in the form of thin films grown on TiN substrate. A critical thickness, ≈1.95 nm, at which the pseudomorphic growth cannot be preserved and after which the cubic phase transforms into its hexagonal counterpart, has been quantified. Details of the structural transformation were simulated. The present studies, by means of crystal-chemical atomic dynamics based on the first-principles calculations, provide in situ physical details on an atomic scale of the thickness-dependent structural transformation, which are hardly observed in experiments.