Unlike multi-layered anti-reflection coatings, this one is inherently broadband, and works at a wide range of angles.
The structure has been formed into the surface of a hard coating (>’3H’ in pencil terms) on a flexible substrate.
To make it, the flexible film with an un-cured organic hard coating is pressed against a sheet of glass on which a closely-packed single layer of ~100nm SiO2 beads has been bonded.
Pushed into the coating, the spherical beads leave an array of almost-touching concave dimples in the coating surface. These dimples are the anti-reflective structure which, after pressing, is cured using ultra-violet to harden it.
Flexible is preserved, with the anti-reflection film bending around an 8mm diameter rod without damage, and the hard coating is “favourable for touch panels”, said the team.
Over the whole thing, the researchers applied a fluoroalkyl hydrophobic coating with “great self-cleaning characteristics”, said the team to help shun dust and fingerprints.
Polyethylene terephthalate (PET) and triacetyl cellulose (TAC) are used for the substrate and, as an aside, the bead-covered glass sheet, used to form the dimples, itself has anti-reflection properties. An added advantage of the technique is that the embossing tool makes itself as the SiO2 beads self-assemble into a suitable close-packed pattern when there are spin-coated onto the glass surface ready for bonding.
Mathematical models that describe the optical performance of the coating have been created. These and the coating are described in the Optical Society of America paler ‘Broadband antireflection film with moth-eye-like structure for flexible display applications’.
This is not the first time moth eyes have inspired anti-refleaction coatings. Anders in the UK offers such a coating for displays (pictured, right), and the University of Surrey is proposing a graphene-based one to improve solar cells.