Influence of system configuration on the properties of Sol-Gel spin coating TiO₂-ZnO films: A comparison of single-layer, composite, and bilayer

This study investigates the influence of system configuration single-layer, composite, and bilayer on the structural, morphological, and optical properties of TiO₂-ZnO thin films. Four different structural designs were fabricated using the sol–gel spin-coating method: TiO₂, ZnO, TiO₂:ZnO composite and ZnO/TiO₂ bilayer. Structural analysis revealed that the ZnO/TiO₂ bilayer exhibited characteristic diffraction peaks corresponding to both crystalline oxides, confirming the formation of a dual-phase heterostructure. However, the TiO₂: ZnO composite film does not exhibit discernible Bragg reflections within the scanned 2θ range. The single layer TiO₂ and ZnO films displayed the expected anatase (101) and hexagonal (100) and (002) crystallographic orientations, respectively. Surface morphology analysis indicated apredominantly compact and relatively smoothfor TiO₂. The ZnO Several elongated surface features with lateral dimensions of ∼ 954 nm, 981 nm, and 1009 nm are observed. These features may correspond to coalesced grains or preferentially oriented growth structures formed during thermal treatment. All thin film configurations exhibited high optical transparency exceeding 60% in the 350–900 nm wavelength range. The optical band gap values varied with film configuration, ranging from 3.52 to 4.13 eV. The ZnO/TiO₂ bilayer showed the lowest band gap value (3.52 eV), which can be attributed to interfacial interactions at the heterojunction.