Tuning optical and structural properties of TiO2/SiO2 Anti-Reflective coatings via plasma processing

• Argon plasma jet treatment significantly reduces surface reflectance of TiO 2 /SiO 2 multilayer anti-reflective coatings, achieving an average reflectance as low as 0.45 % in the visible range (450–750 nm). • Plasma exposure time (5–15 min) enables tunable optical properties, with optimal performance at 15 min, beyond which surface degradation occurs. • Surface smoothing and reduced effective refractive index are attributed to plasma-induced cleaning, nanoscale restructuring, and formation of a graded interfacial layer — confirmed by AFM and optical modeling. • Optical emission spectroscopy (OES) reveals that excited argon metastables (Ar*) dominate the plasma, with minor ambient-air-derived species (O, N 2 , OH) contributing to post-treatment surface hydroxylation. • The study demonstrates a simple, controllable, post-deposition plasma method to enhance anti-reflective performance without altering the multilayer deposition process — highly relevant for photovoltaic and optoelectronic applications. Anti-reflective coatings are essential for enhancing the efficiency of photovoltaic systems by minimizing surface reflections. In this study, TiO 2 and SiO 2 thin films were deposited on silicon substrates via sputtering and subsequently treated with an argon plasma jet for 5, 10, and 15 min. Optical emission spectroscopy confirmed the presence of active plasma species. Plasma treatment significantly reduced surface reflectance in the 450–750 nm range from 2.38 % to 0.59 %, 0.48 %, and 0.45 %, respectively consistent with Lumerical simulations. A concurrent decrease in refractive index was also observed. Structural analyses revealed the anatase phase prior to thermal treatment, evolving into a mixed anatase–rutile phase with enhanced crystallinity post-treatment. Moreover, plasma modification lowered surface roughness and improved coating uniformity, as confirmed by FE-SEM and AFM.