Influence of PEO, PDMAA and corresponding di- and triblock copolymers on the optical properties of niobia thin films

The present study aims at investigation of the influence of poly(ethylene oxide) (PEO), poly(N, N-dimethylacrylamide) (PDMAA) and corresponding block copolymers (PEO-b-PDMAA and PDMAA-b-PEO-b-PDMAA) on the formation of porosity in thin Nb2O5 films using evaporation induced self-assembly (EISA) method. The addition of copolymer solution to Nb sol provoked phase separation and after appropriate annealing a system of pores was generated in the spin-on thin film. The annealing regimes providing complete removal of the polymer from the pores were optimized through Thermogravimetric Analysis (TGA). The morphology and structure of the films were studied by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The optical parameters of the films, along with their thicknesses were determined from reflectance spectra and nonlinear curve fitting. The influence of copolymer structure and composition on the optical properties of thin Nb2O5 films was established and the tuning of refractive index in wide range was demonstrated.