Flower-inspired tunable hierarchical wrinkles for broad-angle structural color*

The cuticle on the epidermal cells of some flower petals forms nano-ridges. The hierarchical grating structures that selectively show broad-angle iridescence can enhance the foraging efficiency of pollinators. Although efforts have been devoted to mimicking this unique broad-angle structural color, the intrinsic tunability offered by natural systems to control such a broadened spectrum is still absent in synthetic models. In this work, we present a biomimetic design, based on hierarchical wrinkling of thin film multilayers, to precisely control the broad-angle diffraction. The wrinkling morphology programs the diffraction pattern: the small wrinkles control the diffraction angles, and the large wrinkles broaden the observable range of the diffraction. The hierarchical wrinkling system only occurs within a limited range of material properties and conditions. The control of the expression of structural color resembles the flowers' tunability of structural color in different regions. We anticipate that our findings will play a foundational role in the rational design of wrinkling photonics with broad-angle iridescence.