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Unconsciously allowing light to pass through the interface: A team from Hangzhou Institute of Science and Technology and Zhejiang University innovatively prepares high-performance broadband wide-angle anti reflection films
Reducing the reflection loss of light at interfaces is an eternal core challenge in fields such as optical imaging, solar energy utilization, and display technology. Traditional multilayer anti reflection films often have complex designs, limited bandwidth, and a sharp decline in performance when incident at large angles. Recently, the joint research team of Hangzhou Institute of Advanced Research, Chinese Academy of Sciences, and Zhejiang University published research results on Laser&Photonics Reviews, reporting a new strategy of magnetron co sputtering combined with wet etching, and successfully prepared high-performance broadband wide-angle antireflection films with gradient refractive index distribution. This work provides a novel and scalable solution for achieving efficient light management.
1、 Technical bottleneck: The structural difficulties of traditional anti reflective films
The principle of anti reflection film is to use destructive interference to counteract reflected light. Traditional solutions are mainly divided into two categories:
Single layer λ/4 film: can only achieve optimal performance at specific wavelengths and perpendicular incidence, with narrow applicability.
Multilayer dielectric film stack: Low reflection can be achieved in a wide wavelength range through design, but its refractive index varies step by step between layers. This abrupt interface can lead to the following issues:
Bandwidth limitation: It is difficult to achieve near zero reflection in an extremely wide spectral range (such as visible near infrared).
Angle sensitivity: As the incident light angle increases, the reflectivity sharply increases, seriously affecting off-axis imaging and collection efficiency.
Stress and adhesion: Thermal stress and lattice mismatch between different material interfaces can easily lead to film cracking or peeling.
2、 Innovation Path: Biomimetic Gradient Structure and Controllable Preparation
The research team is inspired by biological structures such as moth eyes and is committed to preparing thin films with continuous gradient refractive index profiles. This structure allows for a smooth transition of light wave impedance, allowing light to "unconsciously" pass through the interface, thereby achieving near zero reflection in ultra wide frequency bands and large incident angle ranges.
The team broke through convention and developed a novel preparation route of "deposition first, etching later". The core process flow and structural evolution are shown in the following figure:
The two core steps of this technological roadmap are:
Magnetron Co sputtering:
The team simultaneously used SiO ? and Al ? O3 as target materials, and deposited SiAlO ? mixed thin films with uniformly adjustable chemical composition (Si/Al ratio) on the substrate by precisely controlling their respective sputtering powers.
The key advantage of this method lies in the high uniformity of the components at the nanoscale, laying the foundation for the subsequent formation of uniform gradient structures.
Wet Etching:
By utilizing the difference in selective dissolution of Al ? O ∝ and SiO ? in specific etchants, the deposited SiAlO ? thin film is subjected to wet etching treatment.
The etchant preferentially dissolves the Al rich region, while the Si rich region is preserved. By precisely controlling the etching time and concentration, the process gradually occurs from the surface to the interior, ultimately successfully constructing a continuous gradient refractive index distribution structure from the surface layer (close to the refractive index of air) to the bottom layer (close to the refractive index of the substrate) inside the thin film.
3、 Excellent performance: broadband, wide-angle, low reflectivity
The performance test results show that the gradient refractive index anti reflection film prepared by this method performs well:
Ultra wide band: In the ultra wide spectral range of 400-1500 nm, the average reflectivity is suppressed to<1.5%, far exceeding traditional λ/4 films.
Ultra wide angle: Even under a large angle of 60 ° incidence, the film can maintain extremely low reflectivity, solving the core pain point of traditional film systems that are angle sensitive.
Excellent mechanical strength: because the film itself is an inorganic oxide after sintering, its hardness, wear resistance and adhesion are superior to many organic or aerogel based anti reflective structures.
4、 Conclusion and Prospect
The work of the Hangzhou Institute of Science and Technology and the Zhejiang University team successfully transformed the biomimetic gradient refractive index structure from a concept to a reality that can be accurately prepared through the clever combination of magnetron sputtering and wet etching. This preparation strategy is not only innovative in design, but also easy to expand and has good compatibility with existing optical device manufacturing processes.
This technology is expected to bring performance improvements to many fields:
Photovoltaic industry: Improve the capture efficiency of solar cells for large angle incident light such as dawn, dusk, and cloudy days, and increase daily power generation.
High end optical imaging: used in complex optical systems such as cameras, microscopes, and drone lenses to eliminate stray light and improve imaging contrast and clarity.
Flexible display and touch panel: reduces surface reflection and significantly enhances visibility in strong light environments.
This work has opened up a new technological path for the development of high-performance anti reflective optical coatings, demonstrating the enormous potential of industry university research integration in solving cutting-edge scientific problems and industrial application challenges.
