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

Abstract V 0.5 Mo 0.5 N x /MgO(001) alloys with the B1-NaCl structure are grown by ultra-high-vacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N 2 atmospheres at temperatures T s between 100 and 900 °C. Alloy films grown at T s  ≤ 500 °C are polycrystalline with a strong 002 preferred orientation; layers grown at T s  ≥ 700 °C are epitaxial single-crystals. The N/Metal composition ratio x ranges from 1.02 ± 0.05 with T s  = 100–500 °C to 0.94 ± 0.05 at 700 °C to 0.64 ± 0.05 at T s  = 900 °C. N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter a o from 4.212 A with x = 1.02 to 4.175 A at x = 0.94 to 4.120 A with x = 0.64. V 0.5 Mo 0.5 N x nanoindentation hardnesses H and elastic moduli E increase with increasing T s 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 V 0.5 Mo 0.5 N x films exhibit higher toughnesses than that of the parent binary compound VN. V 0.5 Mo 0.5 N x films deposited at higher T s also exhibit enhanced wear resistance. Valence-band x-ray photoelectron spectroscopy analyses reveal an increased volume density of shear-sensitive d-t 2g – d-t 2g metallic states for V 0.5 Mo 0.5 N x compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., with increasing N-vacancy concentration.