Growth and mechanical properties of 111-oriented V_0.5Mo_0.5N_x/Al₂O₃(0001) thin films

Pseudobinary V_0.5Mo_0.5N_x(111) alloys with the B1-NaCl crystal structure are grown on Al₂O₃(0001) substrates in an ultra-high-vacuum system by reactive magnetron sputter deposition in mixed Ar/N₂ atmospheres at temperatures T_s between 100 and 900 °C. Nitrogen-to-metal, N/(V + Mo), fractions x vary monotonically from 0.9 ± 0.1 with T_s = 100 °C to 0.4 ± 0.1 at T_s = 900 °C. Nitrogen loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter a_o from 4.21 ± 0.01 Å at T_s = 300 °C to 4.125 ± 0.005 Å with T_s = 900 °C. Scanning electron micrographs of cube-corner nanoindents extending into the substrate show that the films are relatively ductile, exhibiting material pile-up (plastic flow) around the indent edges. Nanoindentation hardnesses H and elastic moduli E, obtained using a calibrated Berkovich tip, of V_0.5Mo_0.5N_x(111) layers increase with increasing T_s (decreasing x) from 15 ± 1 and 198 ± 5 GPa at 100 °C to 23 ± 2 and 381 ± 11 GPa at 900 °C. These values are lower than the corresponding results obtained for the 001-oriented V_0.5Mo_0.5N_x films. In addition, film wear resistance increases with increasing T_s, while the coefficient of friction, under 1000 μN loads, is 0.09 ± 0.01 for all layers.