TiO 2 sol-gel thin films: role of acidic and basic pH on physical characteristics

Abstract

In this work, we discuss the effects of acidic and basic pH on the structural, morphological, and optical properties of TiO₂ sol-gel thin films deposited on glass substrates by the dip coating method. X-ray diffraction (XRD) and Raman spectroscopy (RS) show that all the samples are polycrystalline and possess anatase structure with preference orientation along the (101) direction. It is found that crystallite size decreases with the increasing pH of the sol for both acidic and basic pH. Atomic force microscopy (AFM) demonstrated a homogenous grain distribution and smooth surface of all films. The surface roughness is influenced by the pH of the sol. UV-visible spectroscopy revealed a higher level of transparency for all films. The deposition medium's pH significantly influences the thin films' optical properties, particularly the direct and indirect band gaps, and refractive index. Photoluminescence measurements revealed a strong violet-blue emission band whose intensity depends strongly on the pH of the sol. Particularly, the emission intensity from the film deposited at a pH value of 10 is significantly lower and exhibited a distinct spectral signature compared to the other samples.