Black and white fused silica: modified sol-gel process combined with moth-eye structuring for highly absorbing and diffuse reflecting SiO2 glass.

Diffuse reflecting (white) and highly absorbing (black) fused silica based materials are presented, which combine volume modified substrates and surfaces equipped with anti-reflective moth-eye-structures. For diffuse reflection, micrometer sized cavities are created in bulk fused silica during a sol-gel process. In contrast, carbon black particles are added to get the highly absorbing material. The moth-eye-structures are prepared by block copolymer micelle nanolithography (BCML), followed by a reactive-ion-etching (RIE) step. The moth-eye-structures drastically reduce the specular reflectance on both diffuse reflecting and highly absorbing samples across a wide spectral range from 250 nm to 2500 nm and for varying incidence angles. The adjustment of the height of the moth-eye-structures allows us to select the spectral position of the specular reflectance minimum, which measures less than 0.1%. Diffuse Lambertian-like scattering and absorbance appear nearly uniform across the selected spectral range, showing a slight decrease with increasing wavelength.

Inverse Moth Eye Nanostructures with Enhanced Antireflection and Contamination Resistance.

Moth-eye-inspired nanostructures are highly useful for antireflection applications. However, block copolymer micelle lithography, an effective method to prepare moth eye nanopillars, can only be used on a limited choice of substrates. Another drawback of nanopillar substrates is that contamination is easily absorbed, thereby reducing transmittance. The production of antireflective surfaces that are contamination-resistant or that can be cleaned easily without the loss of optical properties remains challenging. Here, we describe an approach for creating inverse moth eye nanostructures on other optical substrates than the most commonly used fused silica. We demonstrate its feasibility by fabricating a borosilicate substrate with inverse nanostructures on both sides. The etching of nanoholes on both sides of the substrate improves its transmittance by 8%, thereby surpassing the highest increase of transmittance yet to be obtained with nanopillars on fused silica. More importantly, the substrate with inverse moth eye nanostructures is more robust against contaminations than the substrates with nanopillars. No significant decrease in performance is observed after five cycles of repeated contamination and cleaning. Our approach is transferable to a variety of optical materials, rendering our antireflection nanostructures ideal for applications in touch devices such as touch screens and display panels.