Abstract
Abstract A gyroid crystal possesses a peculiar structural feature that can be conceptualized as a triply periodic surface with a constant mean curvature of zero. The exotic optical properties such as the photonic bandgap and optical chirality can emerge from this three-dimensional (3D) morphological feature. As such, gyroid crystals have been considered as the promising structures for photonic crystals and optical metamaterials. To date, several methods have been proposed to materialize gyroid crystals, including 3D printing, layer-by-layer stacking, two-photon lithography, interference lithography, and self-assembly. Furthermore, the discovery of Weyl points in gyroid crystals has further stimulated these advancements. Among such methods, the self-assembly of block copolymers (BCPs) is unique, because this soft approach can provide an easy-to-craft gyroid, especially at the nanoscale. The unit-cell scale of a gyroid ranging within 30–300 nm can be effectively addressed by BCP self-assembly, whereas other methods would be challenging to achieve this size range. Therefore, a BCP gyroid has provided a material platform for metamaterials and photonic crystals functioning at optical frequencies. Currently, BCP gyroid nanophotonics is ready to take the next step toward topological photonics beyond the conventional photonic crystals and metamaterials. In particular, the intrinsic lattice transformations occurring during the self-assembly of BCP into a gyroid crystal could promise a compelling advantage for advancing Weyl photonics in the optical regime. Lattice transformations are routinely considered as limitations, but in this review, we argue that it is time to widen the scope of the lattice transformations for the future generation of nanophotonics. Thus, our review provides a comprehensive understanding of the gyroid crystal and its lattice transformations, the relevant optical properties, and the recent progress in BCP gyroid self-assembly.
Highlights
1.1 Historical backgroundDiscovered in 1970 by A
We propose that such negatively observable lattice distortions [35, 56] can be a vital aspect of the block copolymers (BCPs) gyroid, widening the scope of BCP gyroid nanophotonics
More than two decades ago, a well-developed bicontinuous network structure was initially created from multiarm star BCPs by Thomas et al [37], and later, they reevaluated this nontraditional structure as a double gyroid structure [38, 39]
Summary
Nanoscale 3D printing (i.e., twophoton lithography [34, 42,43,44,45]) has extended the lower scale limit of the gyroid lattice size to 300–400 nm [42, 44, 46] This process is limited to a single gyroid, which can be applied to only visible photonic crystals [11, 13, 15, 17, 19] and unsuitable for optical metamaterials. The BCP self-assembly can bridge the scale gap of the top-down-accessible gyroid and fulfill the scale requirements for “gyroid nanophotonics” – ranging from optical metamaterials to visible photonic crystals/Weyl materials [11, 13, 15, 17, 19, 29, 30]. Together with the aforementioned grain boundaries with dislocations and disclinations [60,61,62,63], this lattice transformation could represent a technical challenge that further prevents the deterministic optical study and practical usage of the BCP gyroid
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