Broadband\nand Crack-Free Antireflection Coatings by\nSelf-Assembled Moth Eye Patterns

Abstract

We report broadband and quasi-omnidirectional\nantireflective (AR)\nstructures inspired to the nipple arrays of moth eyes. These nanocoatings,\nbased on thin elastomeric films, are prepared by simple self-assembly\nprocessing of a co-polymer specifically designed to this purpose,\nand PDMS replica molding. Typically, their surface is covered by a\ncompact distribution of hemispherical nanodomes of about 250 nm in\ndiameter and about 100 nm in height. When these novel nanostructures\nare applied on a single glass surface, a maximum of 2% transmission\nenhancement (equivalent to a 50% reduction of the reflected component)\ntowards wavelengths ranging from visible to near IR region is obtained.\nA considerable AR power is observed also at a wide range of incident\nangles ranging from normal to 50°. These properties could be\nattributed to an optimized graded refractive index profile resulting\nfrom the randomly distributed and close-packed nanodomes. Moreover,\nthanks to their elastomeric nature, these crack-free films can be\neasily applied on glass, as stickers, and periodically replaced, thus\noffering the possibility of easy dirt removal from an optical device.