An investigation was made of the effect of N vacancies upon the mechanical properties of epitaxial δ-TiNx(001) layers with x = 0.67 to 1.0. The relaxed lattice parameter increased linearly with x, in good agreement with ab initio density functional calculations; thus indicating that deviations from stoichiometry were entirely due to anion vacancies. The

hardness increased continuously, while the elastic modulus decreased with increasing N-vacancy concentration. The observed vacancy hardening was attributed to a reduced dislocation mobility which arose from an increase in the rate-limiting activation energy for cation migration.

Vacancy Hardening in Single-Crystal TiNx(001) Layers. C.S.Shin, D.Gall, N.Hellgren, J.Patscheider, I.Petrov, J.E.Greene: Journal of Applied Physics, 2003, 93[10], 6025-8