Moiré nanosphere lithography: use colloidal moiré patterns as masks

Nanosphere lithography (NSL) uses self-assembled layers of monodisperse micro-/nano-spheres as masks to fabricate plasmonic metal nanoparticles. Different variants of NSL have been proposed with the combination with dry etching and/or angled-deposition. These techniques have employed to fabricate a wide variety of plasmonic nanoparticles or nanostructures. Here we report another promising extension - moire nanosphere lithography (MNSL), which incorporates in-plane twisting between neighboring monolayers, to extend the patterning capability of conventional NSL. In conventional NSL, the masks, either a monolayer or bilayer, are formed by spontaneous self-assembly. Therefore, the resulted colloidal crystal configurations are limited. In this work we used sequential stacking of polystyrene nanosphere monolayers to form a bilayer crystal at the air/water interfaces. During this layer-by-layer stacking process, a crystal domain in the top layer gains the freedom to positon itself in a relative angle to that in the bottom layer allowing for the formation of moire patterns. Subsequent O2 plasma etching results in a variety of complex nanostructures that have not been reported before. Using etched moire patterns as masks, we further fabricated the corresponding gold nanostructures and characterized their scattering optical properties. We believe this facile technique provides a new strategy to fabricate novel and complex plasmonic nanostructures or metasurfaces.