Abstract
Structural hierarchy and complex 3D architecture are characteristics of biological photonic designs that are challenging to reproduce in synthetic materials. Top–down lithography allows for designer patterning of arbitrary shapes, but is largely restricted to planar 2D structures. Self-assembly techniques facilitate easy fabrication of 3D photonic crystals, but controllable defect-integration is difficult. In this paper we combine the advantages of top–down and bottom–up fabrication, developing two techniques to deposit 2D-lithographically-patterned planar layers on top of or in between inverse-opal 3D photonic crystals and creating hierarchical structures that resemble the architecture of the bright green wing scales of the butterfly, Parides sesostris. These fabrication procedures, combining advantages of both top–down and bottom–up fabrication, may prove useful in the development of omnidirectional coloration elements and 3D–2D photonic crystal devices.
Highlights
Top-down nanofabrication based on planar lithography has been the workhorse of modern nanotechnology, enabling the current microelectronics industry as well as the development of a wide range of platforms
We found that many common polymers were not suitable substrates for a successful deposition of a second inverse-opal films (IOFs), even after surface activation by oxygen plasma, we found that growth of good-quality IOFs was possible on films of cured SU-8
Using simple chemical surface-modifications and the unique wetting properties of the IOFs, we have shown that we are able to spin-coat and pattern resist layers on top of IOFs that show good adhesion to the top of the porous surface, but no penetration inside of the pores
Summary
Top-down nanofabrication based on planar lithography has been the workhorse of modern nanotechnology, enabling the current microelectronics industry as well as the development of a wide range of platforms (photonics, microfluidics, etc.). Bottom-up techniques based on self-assembly have emerged as a powerful platform for templating structures that are patterned in 3D with feature sizes ranging from a few nanometers to several microns [10,11,12,13,14,15,16,17,18,19] Unlike their top-down counterparts, they allow scalable 3D patterning of materials. In this paper we develop techniques to build stacks of self-assembled porous 3D-photonic crystals and lithographically patterned planar defect layers with comparable feature-sizes to the pores. This type of structural hierarchy is found in the bright green wing scales of the butterfly, Parides sesostris. We developed two techniques to incorporate lithographically patterned planar layers on top of or inside of self-assembled 3D porous inverse-opal films
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