This study explores the structural, morphological, optical, and gas-sensing characteristics of titanium dioxide (TiO2) thin films with thicknesses of 90, 130, and 160 nm, both before and after decoration with gold (Au/TiO2) and silver (Ag/TiO2) nanoparticles. XRD confirmed the formation of the pure anatase phase, with crystallite size increasing from 13.7 to 14.7 nm and microstrain decreasing from 12.05 × 10–3 to 11.18 × 10–3 as film thickness increased. Scanning electron microscopy revealed a thickness-dependent grain growth (15.4 ± 3–34.7 ± 4.5 nm), while the successful decoration with Au nanoparticles enlarged the particle size to 19 ± 3.5–37.9 ± 5 nm. EDX spectroscopy confirmed stoichiometric TiO2 composition, diffusion of substrate elements (Na, Ca, Mg, and Si), and controlled metal loading (Au: 5.8–10.3 wt %; Ag: 1.4–2.8 wt %). Spectroscopic ellipsometry results indicated refractive indices of 2.3–3.4 and optical band gaps between 3.44–3.60 eV, suggesting improved crystallinity and reduced defect density with increasing thickness. Transmission spectroscopy under CO2 and air atmospheres revealed negligible response for bare glass and pure TiO2, whereas Au/TiO2 and Ag/TiO2 films exhibited localized surface plasmon resonance (LSPR) dips at 520–550 nm and 450–500 nm, respectively. Upon CO2 exposure, Ag/TiO2 showed red-shifts of 10–15 nm and transmission changes of 5–8%, while Au/TiO2 exhibited larger shifts (12–20 nm) and 6–10% modulation. Transmission change ratio analysis confirmed the superior sensitivity of Au/TiO2 (TCR up to −0.50) compared to Ag/TiO2 (TCR up to 0.20), demonstrating their potential for efficient, label-free optical CO2 sensing.
Sadia et al. (Fri,) studied this question.