Structure and properties of NbN and TaN films prepared by ion beam assisted deposition

Niobium nitride NbNx and tantalum nitride TaNx films were deposited on 316L austenitic stainless steel and silicon wafer substrates by evaporation of niobium and tantalum under simultaneous nitrogen ion irradiation, applying an acceleration voltage between 2 and 20 kV, In order to study the influence of the nitrogen content, the atom-to-ion transport ratio Nb, Ta/N was varied. The compositional and structural characterization of the films were carried out using Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. It was observed that the surface morphology strongly depends on the deposition conditions. X-ray diffraction patterns showed that the crystal structure of the films was changed from nitride to solid solution when the transport ratio was increased from 1 to 10, respectively. The crystal structure of the films deposited at Nb, Ta/N = 6 and 10 had the feature of a nitrogen supersaturated bcc solid solution. Electron diffraction revealed the coexistence of an amorphous phase and a fine structured nitride phase in these films. The chemical bonding state of metal atoms observed by XPS changed with increasing the transport ratio, whereas the bonding state of nitrogen atoms was independent of the transport ratio. The corrosion behavior was evaluated in an oxygen saturated 5% sulfuric acid solution, using multisweep cyclic voltammetry measurements. The best corrosion protection was observed for the NbN film at an transport ratio of Nb/N = 2 and for the Ta-N solid solution at Ta/N = 6.