The effect of heat treatment on structural and electronic properties of niobium nitride prepared by a thermal diffusion method

Niobium nitride (NbNx) coatings were prepared onto Nb substrate by thermal diffusion at high temperatures. The formation of NbNx coating by thermal diffusion was studied in the range of 1250–1500°C at constant nitrogen background gas pressure (1.3×10−3Pa) and processing time (180min). The electronic and crystal structures of the NbNx coatings were investigated. It was found that nitrogen diffuses into Nb forming the Nb-N solid solution (bcc) α-NbN phase that starts to appear above 1250°C. Increasing the processing temperature gives richer α-phase concentration. Besides, X-ray absorption spectroscopy (XAS) was performed to study the electronic structure of the NbNx layer. The results of the electronic structural study corroborate the crystal structural analysis. The Nb M3,2 edge X-ray absorption spectroscopy (XAS) spectrum shows strong temperature dependence. At the highest processing temperature (1500°C), the number of d holes increased. Electrostatic interaction between d electron and core hole was increased due to nitrogen diffusion into the niobium. For the studied conditions, only the α-NbN was observed in the X-ray diffraction patterns.