Nanoporous Silicon Dioxide Films for Large Area and Low-Cost Fabrication of Ultra-Low Refractive Index Coatings

Ultralow refractive index films can reduce the reflection loss of light propagating between different media, which is crucial for enhancing the performance and efficiency of optical components. This work presents an approach to the production of ultralow refractive index thin films based on magnetron cosputtering and subsequent selective chemical etching, where a nanoporous silicon dioxide film with a variable refractive index is fabricated by the sacrificial method of forming random holes with a size less than 100 nm. The effective refractive index can be adjusted from 1.1 to 1.46 by simply controlling the sputtering power ratio of the silicon target to the aluminum target. The antireflection properties of ultralow refractive index films have been verified, and their process reproducibility and environmental reliability have been evaluated. The results demonstrate the efficacy of this technique as a viable solution for large-area, low-cost, and high-performance fabrication of ultralow refractive index coatings, which have great potential for the preparation of industrial-scale antireflective films.