Raman spectroscopy of dip-coated and spin-coated sol–gel TiO₂ thin films on different types of glass substrate

The photoinduced self-cleaning and super-hydrophilic properties of titania (TiO₂) coated glasses are considered to be utilized in many applications. The photocatalytic activity of titania is inherent to the glass composition and to the deposition method. Particularly sodium ions diffused to the titania film from the substrate have tremendous impact on its crystallinity. The deposition method influences surface, structure, and the density of the film. This study aims to provide new findings regarding the mechanism of crystallization of sol–gel synthesized titania and its thin films deposited by means of two different methods (dip-coating and spin-coating) onto the glass substrate with a high content of sodium ions (soda-lime glass) and without sodium ions (quartz glass). The main attention is devoted to Raman spectroscopy and Raman point-to-point mapping of the films. The content and the chemical state of the sodium ions were judged using the XPS. It is shown that the dip-coating method led to dense compact material. In this case the crystallization is localized in randomly distributed centers of nucleation. Contrary the spin-coated samples embodied a web-like pattern of cracks, from which the crystallization proceeds throughout the film. Additionally SEM, AFM, XRD, GDS, UV–VIS methods were performed to support the results.