V0.5Mo0.5Nx/MgO(001): Composition, nanostructure, and mechanical properties as a function of film growth temperature

V0.5Mo0.5Nx/MgO(001) alloys with the B1-NaCl structure are grown by ultra-high-vacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N2 atmospheres at temperatures Ts between 100 and 900 °C. Alloy films grown at Ts ≤ 500 °C are polycrystalline with a strong 002 preferred orientation; layers grown at Ts ≥ 700 °C are epitaxial single-crystals. The N/Metal composition ratio x ranges from 1.02 ± 0.05 with Ts = 100-500 °C to 0.94 ± 0.05 at 700 °C to 0.64 ± 0.05 at Ts = 900 °C. 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 at x = 0.94 to 4.120 Å with x = 0.64. V0.5Mo0.5Nx nanoindentation hardnesses H and elastic moduli E increase with increasing Ts from 17 ± 3 and 323 ± 30 GPa at 100 °C to 26 ± 1 and 370 ± 10 GPa at 900 °C. Both polycrystalline and single-crystal V0.5Mo0.5Nx films exhibit higher toughnesses than that of the parent binary compound VN. V0.5Mo0.5Nx films deposited at higher Ts also exhibit enhanced wear resistance. Valence-band x-ray photoelectron spectroscopy analyses reveal an increased volume density of shear-sensitive d-t2g - d-t2g metallic states for V0.5Mo0.5Nx compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., with increasing N-vacancy concentration.

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