Fabrication of anti-reflective and imaging nanostructured optical elements

Abstract

Moth eyes minimize reflection over a broad band of angles and colors and lotus leaves minimize wetting over a broad range of breakthrough pressures by virtue of subwavelength structures patterned on their respective surfaces; similar examples of organisms exploiting geometry to attain properties unavailable in bulk materials are abundant in nature. These instances have inspired applications to man-made structures, collectively known as functional materials: for example, self-cleaning/anti-fogging surfaces, and solar cells with increased efficiency. I fabricated a functional surface where both wetting and reflectivity are controlled by geometry. Using a periodic array of subwavelength-sized high aspect ratio cones, patterned on glass and coated with optimized surfactants, I have experimentally shown that we can significantly enhance transmission from the surfaces of a glass slab, and at the same time make the surfaces either superhydrophobic or superhydrophilic, depending on the applications, such as antifogging and self-cleaning glass. Novel lithographic techniques result in high patterning accuracy over large surface areas, and is easily adaptable to nanoimprinting for future mass replication. In addition, an all-dielectric subwavelength-patterned Luneburg lens was fabricated for operation at free-space wavelength of A =1.55 um.