Subwavelength hollow-nanopillared glass with gradient refractive index for ultra-low diffuse reflectance and anti-fogging.

Nanostructured glass with subwavelength hollow nanopillars with a diameter of sub-65 nm was fabricated, showing high optical transmission and ultra-low diffuse reflectance. A simple process involving single-step plasma etching was used on the glass slide coated with a SiO sacrificial film. First, SiO nanodot structures were formed using a plasma-induced anisotropic etching with CF plasma. SiO nanodot array then became a secondary etching mask to form hollow nanopillars on the glass. The hollow structure formed at the upper part reaching up to the apex of the nanopillar had a lower solid fraction, while the lower part had a higher fraction. The refractive index (RI) gradually increased from 1.09 (near the value for air) to 1.42 (near the value for glass). Geometry-induced RI gradient enhanced the light transmission while it significantly reduced diffuse reflectance, particularly in the shorter wavelengths, thus suppressing the haziness or milky appearance of the nanostructured glass. Super-hydrophilic and anti-fogging properties of nanostructured glasses and dental mirrored glasses were also demonstrated with sprayed water and exhaled breath. Results showed that the wettability was enhanced in hydrophilicity and anti-fogging properties by both the hydrophilic nature of the glass and the newly-formed nanostructure. The nanostructured super-hydrophilic glass was also found to have an easy cleaning nature against fine sand dust adhesion by simple air blow or water spraying. Results of this study showed that such a hollow-pillared glass surface with gradient RI and special wettability could be applied to a variety of optical and opto-electronic applications requiring superwetting, such as optical windows for solar cell panels, display panels, light-emitting diodes, and medical devices even with curved surfaces.