Metamaterials are artificially structured materials whose interaction with electromagnetic waves is determined by their structure rather than by their chemical composition. The resulting material properties are not found in nature. Metamaterials that operate at optical frequencies, known as optical metamaterials, have attracted special attention due to their potentially ground-breaking technical applications such as sub-diffraction imaging or invisibility cloaking. The creation of optical metamaterials remains technologically challenging, as it requires fabricating nanometer scale features over macroscopic areas. Top-down lithographic techniques were utilized to create infrared metamaterials, and negative refraction was found in parts of the visible spectrum. However, state-of-the-art lithography is limited by the accessible feature sizes and often results in only microscopic patterning areas. Furthermore, these optical metamaterials aren’t truly three-dimensional (3D) as they are limited to a narrow range of light propagation directions. This research project investigated an alternative bottom-up approach toward the fabrication of 3D optical metamaterials by replicating continuous network structures of self-assembled block copolymers. The ultimate goal has been to realize a material that exhibits a negative refractive index in the visible optical spectrum. Advanced in situ x-ray scattering techniques were used to investigate and fundamentally understand the self-assembly of 3D network structures by means of well-controlled annealing experiments. The goal of these experiments was to overcome the limitations of “self-assembled” optical metamaterials made by current empirical approaches.
