Conformable solid-index phase masks composed of high-aspect-ratio micropillar arrays and their application to 3D nanopatterning.

Three-dimensional (3D) microstructures are essential elements in various technological applications, including optical coatings, [ 1 , 2 ] tissue engineering scaffolds, [ 3 ] microfl uidics, [ 4 ] energy storage devices, [ 5 , 6 ] plasmonics, [ 7 ] and photonic crystals. [ 8 , 9 ] While conventional methods, such as photo lithography and electron beam lithography, are costly and ineffective in the generation of complex 3D patterns over large areas, unconventional methods based on soft lithography, such as nanoimprint lithography (NIL), [ 10 ] nanotransfer printing (nTP), [ 11 ] microcontact printing ( μ CP), [ 12 ] and micromolding in capillaries (MIMIC), [ 13 ] provide simple and inexpensive routes to fabricate complex multidimensional nanostructures. Above all, proximity fi eld nanopatterning (PnP), [ 14 ] which uses elastomeric components similar to those used in soft lithography, can generate complex 3D nanostructures very rapidly over large areas. Optical interference from the conformable elastomers, working as phase shift elements, generates a complex 3D intensity distribution by the Talbot effect, [ 15 ] or self-imaging effect. The diffracted images of surface relief structures are periodically repeated at integer or fractional Talbot distances from the surface of the mask. Pattern resolution in soft lithography is mainly determined by the fi neness and the aspect ratio of elastomeric surface relief structures, which generally consist of poly(dimethylsiloxane) (PDMS), from a Si master that contains the desired relief patterns on its surface. The height of the relief structures is