Single-monolayer SiNx embedded in TiN: A first-principles study

The dynamical and thermodynamic stability of a single monolayer of SiNx sandwiched isostructurally between B1-TiN(001) and (111) oriented slabs are investigated by means of density functional theory. Possible dynamical stabilization of the (001) interface, by distortion of the Si-N bonds, is considered and found to almost, but not completely, remove the phonon instabilities. The (111) interface on the other hand is found to be dynamically stable. We furthermore relax the stoichiometry degree of freedom by allowing for Si vacancies in the lattice and show that the ideal 1:1 SiN stoichiometry in both interfaces are thermodynamically unstable with respect to Si vacancy formation regardless if the system is grown under nitrogen-rich or nitrogen-poor conditions, and therefore ruling out its relevance for performance of real materials.