Optical and physical properties of annealed amorphous niobium oxide thin films

The physical and optical properties of coatings deposited using physical vapor deposition techniques exhibit changes during post deposition annealing. Optical properties including the index of refraction and spectral transmission vary when coatings are annealed. Physical and mechanical properties such as thickness, density, and stress are also impacted by annealing. In this paper, we study the source of these changes by examining the impact of 150-500°C annealing on Nb2O5 films deposited using thermal evaporation and reactive magnetron sputtering. Models based on the Lorentz-Lorenz equation and potential energy considerations explain the data, and rationalize conflicts between previously reported results.