Effects of different compositional ratios on physical structure and optical properties of thin films during alloying of Zn²⁺ and TiO₂

Abstract

A batch of TiO₂ films with different Zn²⁺ compositions are prepared on a single crystal silicon substrate by using sol-gel method to observe the changes in optical and photocatalytic properties in the alloying process of Zn²⁺ and TiO₂. X-ray diffractometer (XRD) is used to observe the changes in the crystal structures of the films in the alloying process and to track the formation of ZnTiO₃ compounds. Scanning electron microscope (SEM) and atomic force microscope (AFM) are used to observe the phenomena of a large number of holes on the surfaces of the films due to the limited solubility of the crystal lattice for Zn²⁺ in the alloying process. X-ray photoelectron spectroscopy (XPS) and optical bandgap are used to observe the changes at a level of the electronic structure of the films in the alloying process of Zn²⁺ with TiO₂. Finally, by degrading the methylene blue solution, it is shown that a small amount of Zn²⁺ doping is completely dissolved in TiO₂, destroying the TiO₂ crystalline quality. As the compositional share of Zn²⁺ continues to increase to 15%, the limited solubility of TiO₂ for Zn²⁺ is verified in the XPS peak fitting, resulting in a large number of hole structures in the film, and the active specific surface area of the film is enhanced, while Zn²⁺ effectively traps the photogenerated e^–/h⁺. In order to continue to observe the effect of Zn²⁺ concentration on TiO₂, we increase the concentration of Zn²⁺ to 40% and observe the phenomenon in the alloying process of Zn²⁺ with TiO₂. It is shown that the appearance of the compound ZnTiO₃ can act as a complex center for e^–/h⁺ and a significant decrease in the percentage of TiO₂ leads to a gradual decrease in the photocatalytic efficiency of the films after alloying.