Elevating performance of AlOxFy anti-reflection coating via controllable HF vapor fluorination

The introduction of anti-reflective coatings (ARCs) to optical devices has provided a simple and effective solution to improve their power efficiency. Among the various methods of preparing ARCs, the solution process is widely applied due to its simplicity, scalability, and naturally formable pores embedded in the film, which effectively reduce the refractive index of the material. Additionally, since low refractive index materials are always preferred for an effective ARC, strategies of fluorine substitution have been considered. Herein, we successfully introduce fluorine into Al2O3 ARCs by controlled HF vapor through abundant pores in the film. The exposure and reaction conditions were finely tunable, resulting in a precisely controlled amount of fluorine in the AlOxFy ARC. Finally, the gaseous HF vapor fluorination resulted in an effective porous ARC on a sapphire window by matching the refractive index between the surrounding media; thus, fluorinated ARC improves transparency. The maximum and the average transmittances of the ARC-applied window reach ∼99.15% and ∼97.04%, respectively. The suggested fluorination method is anticipated to have broad applicability for situations where surface chemistry modification is necessary. Highly reliable and controllable, this strategy can be used with complicated architectures without causing structural damage.