Synthesis of low oxygen concentration molybdenum nitride films

Polycrystalline, small grain size, 15 μm thick MoxN (x=1 and 2) films containing ≈60 at.% γ-Mo2N and ≈40 at.% δ-MoN and void of Auger detectable concentrations of molybdenum oxides, have been prepared on 50-μm thick nitrided Ti substrates via programmed reaction and subsequent anneal at 750°C for 2 h of the precursor MoO3 films with NH3. The latter films were prepared via liquid spray pyrolysis of an MoCl5/methanol mixture in air at 500°C. By contrast, residual MoO2 occurred near the film–substrate interface in MoxN films produced using the same programmed reaction but where MoO3 had been deposited on bare Ti substrates. The change in density of MoO3 (ρ=4.69 g cm−3) to γ-Mo2N (ρ=9.50 g cm−3) and δ-MoN (ρ=9.05 g cm−3), as well as the nature of the topotactic conversion, produced grains which had a calculated average size of 10 nm and which exhibited good adhesion to the substrate. Variations in the conversion heating rates and the NH3 flow rates also affected both the phase composition and the average grain size of the intermediate and the final reaction products. Scanning electron microscopy (SEM) of the MoxN films revealed a highly porous surface morphology.