Influence of annealing temperature on structural, morphological and optical properties of nanostructured TiO2 thin films

Abstract

Thermal annealing is widely used to improve crystal quality, which affects electrical and structural properties by reducing study defects in materials. Therefore, enormous research efforts were focused on the control of material surface nanostructure through annealing processes, which is of interest for various technologies. However, no work providing a detailed explanation for the structural, morphological and optical parameters of nanostructured TiO2 thin films deposited on glass at temperature above 500°C by the sol–gel dip coating method has been presented to date. In this work, we have grown nanostructured TiO2 thin films by sol–gel dip coating method on glass substrates at room temperature and studied the effects of annealing temperature from 200 to 700°C on optical performance, microstructural changes and surface morphology evolution. The results of this work may be summarised as follows: the X-ray diffraction results show that annealed TiO2 thin films have anatase crystal structure, and the intensities of the peaks of the crystalline phase increased with the increase in annealing temperature; from atomic force microscopy images, distinct variations in morphology of the thin films were also observed; and optical results show that TiO2 films exhibit high visible transmittance, and it has a maximum transmittance of ∼93·61% at 500°C annealing temperature. The optical band gap of the as grown thin films decreases from 3·68 to 3·31 eV with the increase in annealing temperatures. The TiO2 thin film annealed at 500°C has the best optical property. The change in structural, morphological and optical properties with annealing temperature demonstrates that this material has a potential to be used as a novel technology such as nanoelectronics and possibly nano-optoelectronic devices based on nanomaterial for insulating, semiconducting and electron and/or hole blocking layer, etc.