Optimized Al₂O₃–TiO₂ nanolayers prepared by atomic layer deposition as transparent high-performance corrosion-barrier coatings for silver

Silver is highly susceptible to tarnishing in sulfur-containing environments, creating a need for protective coatings that preserve its original appearance. Here, mixed Al₂O₃–TiO₂ nanolayers were deposited on high-purity silver by atomic layer deposition (ALD) and optimized with respect to optical appearance and sulfidation resistance. An intermediate coating thickness of 51.9 ± 2 nm provided the best balance between limited visible-range interference and barrier performance. In accelerated sulfur–toluene tests, this coating delayed pronounced tarnishing to ∼14 h, compared with ∼1 min for uncoated silver, corresponding to an approximately 840-fold extension in the time to full tarnishing. X-ray photoelectron spectroscopy, ellipsometry, Raman spectroscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and scanning electron microscopy confirmed the formation of continuous, conformal mixed Al–Ti oxide films with oxidized Al–O and Ti–O environments and a near-equimolar to slightly Al-rich cation composition, with Al/Ti ≈ 1.0–1.3. The results highlight ALD Al₂O₃–TiO₂ as a promising approach for protective coatings that combine low visual impact with strong resistance to silver sulfidation.