Broadband circular dichroism in chiral plasmonic woodpiles.

The circular dichroism (CD) of a material is the difference in optical absorption under left- and right-circularly polarized illumination. It is crucial for a number of applications, from molecular sensing to the design of circularly polarized thermal light sources. The CD in natural materials is typically weak, leading to the exploitation of artificial chiral materials. Layered chiral woodpile structures are well known to boost chiro-optical effects when realized as a photonic crystal or an optical metamaterial. We here demonstrate that light scattering at a chiral plasmonic woodpile, which is structured on the order of the wavelength of the light, can be well understood by considering the fundamental evanescent Floquet states within the structure. In particular, we report a broadband circular polarization bandgap in the complex band structure of various plasmonic woodpiles that spans the optical transparency window of the atmosphere between 3 and 4 µ m and leads to an average CD of up to 90% within this spectral range. Our findings could pave the way for an ultra-broadband circularly polarized thermal source.

Directed Self-Assembly of Diamond Networks in Triblock Terpolymer Films on Patterned Substrates.

Block copolymers (BCPs) are particularly effective in creating soft nanostructured templates for transferring complex 3D network structures into inorganic materials that are difficult to fabricate by other methods. However, achieving control of the local ordering within these 3D networks over large areas remains a significant obstacle to advancing material properties. Here, we address this challenge by directing the self-assembly of a 3D alternating diamond morphology by solvent vapor annealing of a triblock terpolymer film on a chemically patterned substrate. The hexagonal substrate patterns were designed to match a (111) plane of the diamond lattice. Commensurability between the sparse substrate pattern and the BCP lattice produced a uniformly ordered diamond network within the polymer film, as confirmed by a combination of atomic force microscopy and cross-sectional imaging using focused ion beam scanning electron microscopy. The successful replication of the complex and well-ordered 3D network structure in gold promises to advance optical metamaterials and has potential applications in nanophotonics.