Comprehensive analysis of thickness-dependent structural, morphological, and optical properties of TiO2 based thin films

In this study, three TiO 2 -based thin film samples were fabricated, and their thickness-dependent optical properties and crystal structures were systematically investigated. The films, with thicknesses of 72 nm, 125 nm, and 283 nm, were deposited onto Si(111) substrates using the DC magnetron sputtering technique. The structural, morphological, and optical properties of the TiO 2 thin films were comprehensively characterized using a combination of analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and spectroscopic ellipsometry. XRD analysis confirmed that the films predominantly crystallized in the anatase phase with a high degree of crystallinity, while SEM images revealed smooth surface morphologies with a low density of structural defects. Raman spectroscopic results demonstrated the strong influence of film thickness and substrate effects on the optical and structural characteristics of the films. In particular, the increased intensity and narrowing of anatase-related phonon modes with increasing thickness indicated a progressive enhancement of crystalline ordering. FTIR spectroscopy and spectroscopic ellipsometry were employed to determine the optical band gap (Eg) values for each film thickness. For the 72 nm thick film, the optical band gap was estimated to be Eg ≈ 3.8–2.84 eV. At this low thickness, the substrate contribution remains significant, and the presence of mixed interfacial phases is evident. The 125 nm thick film exhibited an apparent band gap of Eg ≈ 4.13 eV. At this intermediate thickness, incomplete surface coverage and residual substrate influence result in an upward shift of the interband transition features. In contrast, the 283 nm thick film showed a band gap in the range of Eg ≈ 3.1–3.3 eV, which is consistent with the intrinsic optical properties of anatase TiO 2 . At this thickness, the film fully covers the substrate, effectively suppressing substrate-related optical contributions. These results confirm that the TiO 2 thin films produced in this study exhibit high structural and optical quality, making them promising candidates for applications in photocatalytic and optoelectronic devices. Overall, the findings highlight that precise control of film thickness and thermal treatment parameters is crucial for optimizing the optical and photocatalytic performance of TiO 2 -based thin films.