Fabrication of antireflective hierarchical TiO₂ nanostructures by moth-eye patterning of anodic anodized nanotubes

Herein, we report the fabrication and characterization of a hierarchical TiO₂ structure that exhibits reduced surface reflection. The hierarchical structure, which is a moth-eye-shaped array containing nanotubes, was fabricated by dry-etching a TiO₂ nanotube layer, by using colloidal lithography. The fabricated structure shows a reduced reflectance, compared with that of non-patterned TiO₂ nanotubes. This is because of the graded refractive index of the moth-eye pattern. Furthermore, we investigated the optical properties of gold-decorated moth-eye TiO₂ nanotubes and found that the absorption, which was caused by the plasmonic resonance of gold nanostructures, was further enhanced by coupling with the light-trapping effect.