Christiansen, Alexander Bruun1; Højlund-Nielsen, Emil1; Clausen, Jeppe Sandvik3; Caringal, Gideon Peter5; Mortensen, N. Asger6; Kristensen, Anders6
1 Department of Micro- and Nanotechnology, Technical University of Denmark2 Optofluidics, Department of Micro- and Nanotechnology, Technical University of Denmark3 Department of Photonics Engineering, Technical University of Denmark4 Structured Electromagnetic Materials, Department of Photonics Engineering, Technical University of Denmark5 Technical Information Center of Denmark, Technical University of Denmark6 Center for Nanostructured Graphene, Center, Technical University of Denmark
Inspired by nature, nano-textured surfaces have attracted much attention as a method to realize optical surface functionality. The moth-eye antireflective structure and the structural colors of Morpho butterflies are wellknown examples used for inspiration for such biomimetic research. In this paper, nanostructured polymer surfaces suitable for up-scalable polymer replication methods, such as imprinting/embossing and injection-molding, are discussed. The limiting case of injection-moulding compatible designs is investigated. Anti-reflective polymer surfaces are realized by replication of Black Silicon (BSi) random nanostructure surfaces. The optical transmission at normal incidence is measured for wavelengths from 400 nm to 900 nm. For samples with optimized nanostructures, the reflectance is reduced by 50 % compared to samples with planar surfaces. The specular and diffusive reflection of light from polymer surfaces and their implication for creating structural colors is discussed. In the case of injection-moulding compatible designs, the maximum reflection of nano-scale textured surfaces cannot exceed the Fresnel reflection of a corresponding flat polymer surface, which is approx. 4 % for normal incidence. Diffraction gratings provide strong color reflection defined by the diffraction orders. However, the apperance varies strongly with viewing angles. Three different methods to address the strong angular-dependence of diffraction grating based structural color are discussed.
Proceedings of Spie, the International Society for Optical Engineering, 2013, Vol 8818