V0.5Mo0.5Nx/MgO(001) layers grown at 100-900 °C : composition, nanostructure, and mechanical properties

• V0.5Mo0.5Nx/MgO(001) alloys with the B1-NaCl structure are grown by ultra-highvacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N2 atmospheres at temperatures Ts which are varied from 100 and 900 °C. Alloy films grown at Ts ≤ 500 °C are polycrystalline with a strong 002 texture; layers grown at Ts ≤ 700 °C are epitaxial single-crystals. The N/Me ratio x ranges from 0.64±0.05 with Ts = 900 °C to 0.94±0.05 at 700 °C to 1.02±0.05 with Ts = 500 to 100 °C. The N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter ao from 4.212 Å with x = 1.02 to 4.175 Å with x = 0.94 to 4.121 Å with x = 0.64. V0.5Mo0.5Nx nanoindentation hardnesses H and elastic moduli E increase with increasing Ts from 17±3 GPa and 274±31 GPa at 100 °C to 26±1 GPa and 303±10 GPa at 900 °C. Films deposited at higher Ts also exhibit enhanced wear resistance. Scanning electron micrographs of nanoindents performed in single-crystal V0.5Mo0.5Nx films and films deposited at 100 and 300 °C reveal no evidence of cracking; instead they exhibit material pile-up around the indents characteristic of plastic flow in ductile materials. Valence band x-ray photoelectron spectroscopy analyses show an enhanced volume density of the shear sensitive d-t2g – d-t2g metallic states in V0.5Mo0.5Nx compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., the metallic  states become more populated with the introduction of N vacancies.

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