Nanoimprint is broadly used to pattern thin polymer films on rigid substrates. The resulted patterns can be used either as functional nanostructures or as masks for a pattern transfer. Also, nanoimprint could, in principle, be used for the direct patterning of thermoformable substrates with functional nanostructures; however, the resulted global substrate deformation makes this approach unpractical. Here, we present a new approach for the direct nanoimprint of thermoformable substrates with functional nanostructures through precise maintaining of the substrate shape. Our approach is based on an elastomeric stam soaked in organic solvent, which diffuses into the imprinted substrate, plasticizes its surface, and thereby allows its imprint at the temperature below its glass transition point. Using this approach, we imprinted features at the 20 nm scale, which are comparable to those demonstrated by conventional nanoimprint techniques. We illustrated the applicability of our approach by producing functional antireflective nanostructures onto flat and curved optical substrates. In both cases, we achieved full pattern transfer and maintained the shape of the imprinted substrates, a combination that has not been demonstrated so far. Our approach substantially expands the capabilities of nanoimprint and paves the way to its numerous applications, which have been impossible by existing nanopatterning technologies.
Keywords: AR coating; PDMS; direct imprint; nanoimprint; polymers.