Bionic Approach Moth-Eye Structures

Some literature sources go so far that according to them all subwavelength antireflection reliefs with a gradient of effective refractive index are called moth-eye structures (e.g., [193]), including 2D pyramidal and nanopillar arrays. 

Decades passed before it was technologically possible to mimic such nano-strncmres and fabricate artificial bionic moth eye ARS [191, 194]. Technologically, moth eyes can be produced at a correct scale using lithography, crossing three gratings at 120°. Another approach to fabrication is electron-beam etching. 

Harker et al. produced artificial moth eye structures in silicon, germanium, and diamond [193]. Huang et al. fabricated bio-inspired silicon nanotips as antireflection stmcmres [194]. 

One should mention here the works of Wang who implemented a topology optimization procedure by genetic algorithm to developed a complex optimized surface relief (not a moth-eye structure), as a result claiming efficiencies up to three times over the Yablonovitch limit [195]. 

---