Effect of annealing temperature on the structural, optical, morphological, and photocatalytic properties of TiO2 thin films prepared by sol-gel spin-coating and electron beam physical vapor deposition

TiO2 thin films were prepared by sol-gel spin-coating (SGSC) and electron beam-physical vapor deposition (EB-PVD) methods and annealed at different temperatures (T-a ). X-ray diffraction spectroscopy (XRD) results show that the TiO(2 )films prepared by the SGSC method transformed from the anatase single phase to the coexistence of anatase and rutile with the increase of T-a . However, TiO2 films prepared by the EB-PVD method existed only in the anatase phase, and the crystalline strength was enhanced with the increase of T-a . Meanwhile, particles of TiO2 targets annealed at different T-a showed a rutile phase for TiO2 target particles in the EB-PVD method. The results indicate that the EB-PVD method hinders the nucleation growth and phase transformation of TiO2 films. Scanning electron microscopy and atomic force microscopy also show that the grain size and R- ms of TiO2 thin films prepared by the SGSC method increased with the increase of T-a , and the grain size becomes inhomogeneous when the rutile phase is formed. Ultraviolet-visible results show that the forbidden bandwidth and light absorption capacity increase with increasing T-a . For the EB-PVD method, the grain size and surface roughness gradually increased when the T-a of the films was less than 800 degrees C, while annealing at 800 degrees C changed the direction of growth and nucleation, and also produced surface cracks; XRD verified the hypothesis that the EB-PVD method hinders the nucleation growth as well as the phase transition of the films. Weak differences in the optical absorption properties and bandgap values of the films also indicate that the EB-PVD method hinders the phase transformation of TiO2 films. Finally, the results of degradation of methylene blue (MB) under simulated visible light showed that the films prepared by the SGSC method gradually improved the photocatalytic performance with the enhancement of the crystalline strength of the anatase phase. The TiO2 films prepared by the EB-PVD method improved the photocatalytic performance with the increase of the active area.