Fabrication of dual patterned nanocavities using double layer nanosphere lithography

A new nanosphere lithography technique is presented to produce a periodic nanocavities of two sizes. The process starts by deposition of a bilayer of polystyrene microspheres on photoresist through self assembly as a mask. The spheres act as microlenses to direct UV light both to the centers of the bottom spheres and between these centers, resulting in bigger and smaller nanocavities. The appearance and size of small cavities can be controlled through adjusting exposure and development time. Among the achieved ordered patterns, the diameter of the big cavities ranges from 610 to 660 nm and the small cavities from zero to 250 nm. The diameter of the big cavities and spacing are also tunable by using spheres of different diameters. The approach presented in this paper can be extended to fabrication of mixed arrays of nanocolumns with controlled size.