Large-Scale Nanofabrication of Stacked Nanosphere Lithography Metasurfaces

Metamaterials have the potential to yield flat lenses, diffraction-unlimited microscopes, and even invisibility cloaks. A metamaterial’s optical properties are governed by the spacing and alignment of small nanostructures embedded inside the material. These nanostructures, through electrical and magnetic coupling, may give rise to a negative index of refraction over a specific electromagnetic frequency – a phenomenon not found anywhere in nature.  However, fabrication of theorized Negative Index Metamaterials (NIMs), and other novel structures, has been difficult due to the limitations of 3D nanofabrication. This study proposes a new technique that utilizes Nano-Sphere Lithography (NSL) and spin-coating to stack metasurfaces and create 3D metamaterials. The process was optimized for polystyrene films, 200nm thick, and 25nm thick gold nano-antennas. We demonstrate the stacking of up to 3 NSL-defined metasurfaces, with no indication of a physical limit to how many layers can be stacked. The technique, hence, makes it more feasible to fabricate novel 3D metamaterials while still maintaining the resolution and simple fabrication offered by NSL.