Synthesis and SERS activity of niobium nitride thin films via reduction nitridation of sol-gel derived films

The niobium nitride thin films as the novel substrates for surface-enhanced Raman spectroscopy (SERS) were synthesized via reduction nitridation of Nb2O5 thin films derived by sol-gel method in NH3 gas. The composition, morphology, energy level structure, optical properties and SERS performance of the films were characterized. The XRD and XPS results show that the solid solution niobium oxynitride (NbOxNy) is formed, rather than the stoichiometric Nb4N5 in the thin films. The surface plasmon resonance absorption peak occurred a red shift and became widen, and the band gap of niobium nitride thin films became narrow with the reduction nitridation temperature increasing. Meanwhile, the films surface became rough, which could provide a lot of “hot spots”. As a result, the niobium nitride films have the surface-enhanced Raman spectroscopy activity via electromagnetic field enhancement and charge transfer mechanism. The niobium nitride films obtained at 800 °C show the optimal Raman enhancement performance, for which detection limit of probe molecule R6G is 10−7 M, and the enhancement factor is 4 × 103. In addition, the niobium nitride films possess good uniformity, long-term stability, and high temperature resistance.