Reflections are often a nuisance; they reduce the light that passes through the lenses of cameras and telescopes, and cause distracting glares on displays such as mobile phone screens. Antireflection coatings exist, but they consist of multiple thin films that are expensive to apply. Researchers from Inha University and the Gwangju Institute of Science and Technology in Korea have now developed a straightforward process for fabricating antireflection coatings.1 “Our polymer antireflection films can be used for display units, solar cells and many optical components,” says Han Sup Lee, who led the research team.

Reflections occur when light travels between two media of different refractive indexes — glass, for example, is optically denser than air. The reflections that occur at the air–glass interface are traditionally suppressed by inserting an additional film that reduces the difference between the two refractive indices. The transition between air and glass should ideally be gradual, and such antireflection coatings therefore consist of multiple layers with increasing refractive index.

Fig. 1: Scanning electron microscopy images of the polymer nanostructures. Increasing the etching quality (left to right) in the aluminum oxide template makes the nanostructures more parabolic (right) and so improves the antireflection efficiency.

The alternative approach of Lee and his co-workers takes inspiration from the eyes of moths, which have an antireflection polymer film patterned with nanostructures made from the same material. The best antireflection effect was achieved when the nanostructures had a parabola-like shape (Fig. 1).

The researchers found that aluminum oxide was the perfect template for fabricating the patterned films. Tiny nanometer-sized holes typically form during the passivation of aluminum oxide. These holes were shaped as parabolas through a controlled etching process. The antireflection polymer was then poured into this template, after which the aluminum oxide was removed to make free-standing films. More than 99% of the incident light was transmitted without reflections through these nanostructured films.

Although these results are impressive, the aluminum oxide templates are slow to fabricate. Furthermore, the films cannot be reused indefinitely. However, Lee is optimistic that a commercially suitable process could be developed. “We are currently working on an antireflection fabrication process based on a robust material that can be used continuously in, for example, a roll-to-roll process. We are also trying to make antireflection structures with enhanced surface mechanical stabilities.”