Sol–gel synthesis and spin-coating Nb-doped TiO2 anatase thin films

In this study, undoped and Nb-doped TiO2 thin films were successfully synthesized using sol gel and spin coating methods. The influence of Nb doping ratio on the structural, morphological, optical, Fourier transform infrared spectroscopy (FTIR) and electrical properties of Nb:TiO2 thin films was systematically investigated. Both Raman analysis and X-ray diffraction (XRD) analysis confirmed the formation of anatase phase for all the samples with a preferential orientation along (101) plane and a slight lattice distortions due to Nb incorporation. The crystallite size was reduced from 23.6 nm to19.3 nm with increasing the doping ratio. FESEM images reveal that the surface morphologies of pure and Nb:TiO2 films are dense, smooth, uniform and homogeneous without cracks or pores. The incorporation of Nb into TiO2 host lattice was confirmed by electron dispersion spectroscopy (EDS) analysis. The UV–Vis characterization revealed that all films are highly transparent (∼68–87%) and that Nb doping causes the optical band gap energy shrining from 3.73 eV to 3.64 eV. Moreover, The Fourier transform infrared (FTIR) spectroscopy confirms the successful formation of the TiO2 phase in all samples. The electrical measurement results revealed an improvement in the film’s resistivity and carrier concentration with Nb doping, this was attributed to Nb5+ions substituting Ti4+ site causing the free electrons concentration rise.