The influence of nitrogen pressure on formation of niobium nitride by thermal processing

Abstract The nitridation of niobium by thermal processing at 1300 °C in different nitrogen (N 2 ) gas pressures ranging from 2.6 × 10 −4 to 3.3 × 10 0  Pa was investigated. The NbN x films were grown on the niobium substrate by reactive thermal heating. The effect of nitrogen background pressure on the structure and morphology of the formed NbN x phase was studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The electronic structure of the NbN x films was investigated by X-ray absorption near edge structure (XANES). The phase formation followed a sequence of α-Nb(N)→ β-Nb 2 N when the nitrogen pressure was increased. As the pressure was increased to >1.3 × 10 −3  Pa, the nitride film develop into the α-Nb(N) phase mixed with the β-Nb 2 N phase. Increasing nitrogen pressure results in more β-phase concentration accompanied by an increase of other phases. Higher pressure promotes the diffusion of adsorbed nitrogen, and consequently the formation of different phases of NbN x . The diffusion of nitrogen in the Nb surface and its reactivity governs the phase formation of NbN x . XANES measurements at the Nb M-edge showed strong hybridizations between the Nb 4 d and N 2 p states due to larger covalent contribution to the Nb N bonding. On the basis of these observations our density of state calculation revealed that presence of the β-Nb 2 N phase in NbN x results in a large covalent contribution than that by the α-NbN phase.