Microstructural factors influencing the properties of high surface area molybdenum nitride films converted from molybdenum trioxide films deposited via solution spray pyrolysis

Molybdenum trioxide (MoO3) films, 15 µm thick, have been deposited on 50 µm thick polycrystalline titanium substrates from 250 to 500 °C via liquid spray pyrolysis. Molybdenum pentachloride (MoCl5) dissolved in methanol was used as the molybdenum source; ambient conditions provided the oxygen source. X-ray diffraction (XRD) data indicated that amorphous MoO3 films were produced at deposition temperatures below 400 °C. Randomly orientated polycrystalline MoO3 films were produced at 400 °C and higher deposition temperatures. The deposition temperature also influenced the surface area of the films and their average grain size. Subsequent conversion of the MoO3 films to high surface area (HSA) conductive films containing both γ–Mo2N and δ–MoN was accomplished via programmed reactions with anhydrous NH3 and involved the formation of MoO2 and MoOxN1−x as intermediate phases. The degree of crystallinity, surface area, and average grain size of the MoO3 films strongly influenced the average grain size and surface area of the resultant MoxN films.