Tuning the crystallization temperature of titanium dioxide thin films by incorporating silicon dioxide via supercycle atomic layer deposition

Titanium oxide-based nanomaterials are nowadays of great interest in various application fields such as optics, sensing, photocatalysis, and solar cells. Tuning their physical properties by tailoring the geometry or combining them with different materials further expands their applicability and even allows for the generation of new functionalities. The materials’ crystalline phase also determines its properties and the crystallization behavior can be modified by doping or multilayering thin films with various materials. For instance, the combination of TiO 2 with silicon dioxide (SiO 2 ) renders these composites ideal candidates for coatings applied in harsh environments based on the high chemical and mechanical stability of both materials. Applying such coatings in optics, sensing, or photocatalysis require accurate prediction of the evolution of their properties and crystalline phase during heat treatments within the fabrication and application. Herein, we present the fabrication of SiO 2 -incorporated TiO 2 thin films by supercycle atomic layer deposition (ALD). Specifically, TiO 2 -SiO 2 multilayers with varying material ratios, TiO 2 thicknesses, and individual layer numbers as well as SiO 2 -doped TiO 2 thin films are prepared. Their crystallization behavior is studied by in situ X-ray diffraction during thermal annealing. The structural properties of the composite materials are assessed by X-ray reflectivity, spectroscopic ellipsometry, and transmission electron microscopy before and after annealing. TiO 2 -SiO 2 multilayers show increasing crystallization temperatures from amorphous TiO 2 to anatase with decreasing TiO 2 layer thickness from 50 nm to 4 nm and with increasing number of TiO 2 layers. Their layered structure is retained during annealing while the interfaces roughen slightly. SiO 2 -doped TiO 2 thin films demonstrate increasing crystallization temperatures with increasing SiO 2 contents up to 10 %. The refractive index of these doped structures is tailored by the SiO 2 content. Detailed characterization of ALD deposited SiO 2 -containing TiO 2 thin films could further expand their application in the future by precisely adjusting the fabrication process for the desired material properties and target application. SiO 2 incorporation via supercycle ALD enables precise tuning of TiO 2 thin film crystallization behavior and structural properties for tailor-made coatings.