Influence of thickness and calcination under ammonia gas flow on topographical, optical and photocatalytic properties of Nb2O5 thin films prepared by sol-gel: a comparative study

Nb2O5 thin films have been fabricated by spin coating of niobium alkoxide sols on ITO coated glass substrates. The effects of variation in thickness and calcination conditions (i.e. under oxygen and under ammonia gas flow) on optical and photocatalytic properties of the films was investigated. Two sets of Nb2O5 thin films were prepared. One set of the films (N-1a, N-1b, N-1c and N-1d) were calcined under ammonia gas flow and the other (1a, 1b, 1c and 1d) under oxygen gas flow at 500 A degrees C for 1 h. Thicknesses of the films were found to decrease from a parts per thousand 143.0 to a parts per thousand 121.0 nm upon increasing the rotation speed of the spin coater from 500 to 2000 rpm. The prepared films were characterized by X-ray diffraction, AFM, Ellipsometry and UV-Vis-NIR spectroscopy. Notably, narrowing of band gaps was observed after calcination under NH3 environment. On account of the observed grain sizes and band gap energies, a comparative evaluation of the efficiencies for photocatalytic degradation of methylene blue under UV irradiation was also done.