title: Theoretical and experimental analysis of the structural pattern responsible for the iridescence of Morpho butterflies.
abstract: Morpho butterflies are well-known for their iridescence originating from nanostructures in the scales of their wings. These optical active structures integrate three design principles leading to the wide angle reflection: alternating lamellae layers, "Christmas tree" like shape, and offsets between neighboring ridges. We study their individual effects rigorously by 2D FEM simulations of the nanostructures of the Morpho sulkowskyi butterfly and show how the reflection spectrum can be controlled by the design of the nanostructures. The width of the spectrum is broad (≈ 90 nm) for alternating lamellae layers (or "brunches") of the structure while the "Christmas tree" pattern together with a height offset between neighboring ridges reduces the directionality of the reflectance. Furthermore, we fabricated the simulated structures by e-beam lithography. The resulting samples mimicked all important optical features of the original Morpho butterfly scales and feature the intense blue iridescence with a wide angular range of reflection.
authors.affiliation: Institute for Microstructure Technology, Karlsruhe Institute of Technology (KIT), 76344 Karlsruhe, Germany. radwanul.siddique@kit.edu
authors.forename: Radwanul Hasan
authors.initials: RH
authors.lastname: Siddique
authors.forename: Silvia
authors.initials: S
authors.lastname: Diewald
authors.forename: Juerg
authors.initials: J
authors.lastname: Leuthold
authors.forename: Hendrik
authors.initials: H
authors.lastname: Hölscher
mesh_terms: D000818:Animals; D002080:Butterflies / Q000737:chemistry* / Q000648:ultrastructure*; D003116:Color; D003198:Computer Simulation; D008027:Light; D008953:Models, Anatomic; D008956:Models, Chemical; D012031:Refractometry / Q000379:methods*; D012542:Scattering, Radiation; D014921:Wings, Animal / Q000737:chemistry* / Q000648:ultrastructure*