Optical constants of e-beam evaporated and annealed Nb₂O₅thin films with varying thickness

Niobium pentoxide (Nb2O5) films with different thicknesses were prepared using the electron beam evaporation method and then annealed at temperatures from 300 °C to 800 °C before being characterized by variable-angle spectroscopic ellipsometry, x-ray diffraction, etc. The results showed that the optical constants and microstructures of Nb2O5 films exhibit a strong dependence on the annealing temperature. In the visible light region, the refractive indices show a positive correlation with the annealing temperature from 300 °C to 600 °C, but a negative correlation from 600 °C to 800 °C. The amorphous Nb2O5 film converts into TT- Nb2O5 (pseudo-hexagonal) after annealing at 500–600 °C, and into T-Nb2O5 (orthorhombic) after annealing at 700–800 °C.