Multiple-Patterning Nanosphere Lithography for Fabricating Periodic Three-Dimensional Hierarchical Nanostructures.

While three-dimensional (3D) configurable hierarchical nanostructures have wide ranging applications in electronics, biology, and optics, finding scalable approaches remains a challenge. We report a robust and general strategy called multiple-patterning nanosphere lithography (MP-NSL) for the fabrication of periodic 3D hierarchical nanostructures in a highly scalable and tunable manner. This nanofabrication technique exploits the selected and repeated etching of polymer nanospheres that serve as resists and that can be shaped in parallel for each processing step. The application of MP-NSL enables the fabrication of periodic, vertically aligned Si nanotubes at the wafer scale with nanometer-scale control in three dimensions including outer/inner diameters, heights/hole-depths, and pitches. The MP-NSL method was utilized to construct 3D periodic hierarchical hybrid nanostructures such as multilevel solid/hollow nanotowers where the height and diameter of each level of each structure can be configured precisely as well as 3D concentric plasmonic nanodisk/nanorings with tunable optical properties on a variety of substrates.