Millions of years before people began to fabricate functional nanostructures, biological systems were using periodic nanostructures to produce unique functionalities. For example, moths use hexagonal arrays of non-close-packed nanonipples as broadband antireflection coatings (ARCs) to reduce optical reflectance from their compound eyes. The outer surface of the corneal lenses of moths consists of periodic arrays of conical protuberances, termed corneal nipples, typically of sub-300 nm height and spacing. These arrays of subwavelength structured nipples generate a graded transition of refractive index, leading to minimized reflection over a broad range of wavelengths and angles of incidence. Similar periodic arrays of nanopillars have also been observed on the wings of cicada to render superhydrophobic surfaces for self-cleaning functionality. In this chapter, we reviewed our recent advances in developing self-cleaning moth-eye broadband ARCs on a large variety of substrates, such as crystalline silicon, GaAs, and glass. The motheye nanostructures are templated on the substrate surface by using two scalable bottom-up colloidal self-assembly technological platforms.

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