Inverted hemispherical mask colloidal lithography

This paper presents a cost-effective nanofabrication method for forming large area and high coverage two-dimensional metal nanostructures on flat and curved surfaces. This method starts with a periodic array of hemispherical dimples on polystyrene (PS) film prepared by colloidal lithography with a sacrificial layer of polyacrylic acid (PAA) underneath. After the removal of PAA in water solution, the PS layer is turned over and attached to the substrate to be patterned. An inverted hemispherical mask is formed after oxygen plasma etching. As the holes at the bottom are much larger than those on the surface, the mask is especially suitable for a standard lift-off process. Based on this mask, metal nano-disk and pair-disk arrays, as well as two-dimensional nanostructures on a curved surface, have been fabricated. Optical measurement shows that a surface plasmon resonance exists in a periodic disk array. This method is valuable for the fabrication of a magnifying metamaterial hyperlens in order to eliminate the limitation of optical diffraction.