Large-area flexible 3D optical negative index metamaterial formed by nanotransfer printing

Negative-index metamaterials (NIMs) are engineered structures with optical properties that cannot be obtained in naturally occurring materials ^1-3. Recent work has demonstrated that focused ion beam⁴ and layer-by-layer electron-beam lithography can be used to pattern the necessary nanoscale features over small areas (hundreds of μm²) for metamaterials with three-dimensional layouts and interesting characteristics, including negative-index behaviour in the optical regime. A key challenge is in the fabrication of such three-dimensional NIMs with sizes and at throughputs necessary for many realistic applications (including lenses, resonators and other photonic components ^6-8). We report a simple printing approach capable of forming large-area, high-quality NIMs with three-dimensional, multilayer formats. Here, a silicon wafer with deep, nanoscale patterns of surface relief serves as a reusable stamp. Blanket deposition of alternating layers of silver and magnesium fluoride onto such a stamp represents a process for inking it with thick, multilayer assemblies. Transfer printing this ink material onto rigid or flexible substrates completes the fabrication in a high-throughput manner. Experimental measurements and simulation results show that macroscale, three-dimensional NIMs (>75 cm ²) nano-manufactured in this way exhibit a strong, negative index of refraction in the near-infrared spectral range, with excellent figures of merit.