Optical constants of e-beam evaporated and annealed Nb2O5 thin 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 degrees C to 800 degrees 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 degrees C to 600 degrees C, but a negative correlation from 600 degrees C to 800 degrees C. The amorphous Nb2O5 film converts into TT-Nb2O5 (pseudo-hexagonal) after annealing at 500-600 degrees C, and into T-Nb2O5 (orthorhombic) after annealing at 700-800 degrees C.