Comprehensive study of dual-doped TiO2 thin films: Phase transition, bandgap tuning, and microstructural characterization

This study investigates the transformation effects of chromium doping, and nitrogen co-doping on the structural, morphological, and optical properties of TiO 2 thin films. Phase studies, surface topography, molecular bond analysis, thickness measurement, and bandgap analysis of thin films result in interesting findings. XRD analysis reveals growth in hybrid phases, with notable changes in the doping of TiO 2 thin films. The XPS analysis shows the existence of Ti +3 states in Ti spectra with Ti +4 states for Cr-doped TiO 2 thin films. The induction of oxygen vacancies during the substitution of metal cations (Cr) for Ti 4+ promotes the rearrangement of atoms required for the anatase-to-rutile transformation. Titanium-oxygen interaction and dopant incorporation into the TiO 2 lattice are indicated by the characteristic 435 cm −1 and 375 cm −1 peaks, as well as an increment in bond strength. The shifting of vibration modes confirms the substitution of Cr +3 and N −3 ions, into the TiO 2 lattice. The length of the Ti-O bond is Lengthened and shortened by the replacement of Cr and N. The spectroscopic ellipsometry shows that TiO 2 thin films have a thickness of 102 nm, which decreases to 92 nm after doping with chromium and nitrogen. The surface morphology shows that the average particle size is decreasing as well as surface roughness is decreasing which tells that the surface becoming smooth after doping in TiO 2 thin films. These observations suggest defect accumulation, and grain boundary modifications, leading to doping-induced surface roughening. The UV-Vis transmission spectra show changes in transparency and absorption, with significant contributions from Cr and N dopants. Notably, bandgap measurements reveal an intriguing phenomenon: bandgap narrowing caused by lattice oxygen substitution of nitrogen atoms. The Pure film has a bandgap energy of 3.25 eV, which decreases to 2.28 eV with increasing chromium doping. The chromium-nitrogen co-doped thin film had a bandgap energy of 2.81 eV. This study establishes the relationship and correlation between doping and TiO 2 thin-film properties, which will be extremely beneficial in photovoltaic applications and materials science research.