The impact of nitrogen content and vacancies on structure and mechanical properties of Mo-N thin films

Based on a combined computational and experimental study, we show that besides the thermodynamically stable beta-MoN0.5 and delta(2)-MoN phases, also metastable gamma-MoNx and its ordered relative gamma'-MoNx can be synthesized by physical vapor deposition. The formation of the NaCl-based gamma-MoNx phase is favored for nitrogen concentrations between 23 and 34 at.% (i.e., x = 0.30-0.53). Higher nitrogen contents (close to the 3:2 stoichiometry, hence, MoN0.67) favor the ordering of the vacancies at the nitrogen sublattice (hence, gamma'-MoNx). The highest hardness of similar to 33 GPa is obtained for single-phase cubic-structured gamma-MoN0.53 coatings, whereas the ordered gamma'-MoN0.67 coatings are slightly softer with a hardness of similar to 28 GPa. (C) 2016 Author(s).