Abstract:Structurally colored materials are often used for their resistance to photobleaching and their complex viewing-direction-dependent optical properties. Frequently, absorption has been added to these types of materials in order to improve the color saturation by mitigating the effects of nonspecific scattering that is present in most samples due to imperfect manufacturing procedures. The combination of absorbing elements and structural coloration often yields emergent optical properties. Here, a new hybrid architecture is introduced that leads to an interesting, highly directional optical effect. By localizing absorption in a thin layer within a transparent, structurally colored multilayer material, an optical Janus effect is created, wherein the observed reflected color is different on one side of the sample than on the other. A systematic characterization of the optical properties of these structures as a function of their geometry and composition is performed. The experimental studies are coupled with a theoretical analysis that enables a precise, rational design of various optical Janus structures with highly controlled color, pattern, and fabrication approaches. These asymmetrically colored materials will open applications in art, architecture, semitransparent solar cells, and security features in anticounterfeiting materials.
The work was supported by the National Science Foundation (NSF) under the Award No. DMREF-1533985. Fabrication was carried out at the Harvard Center for Nanoscale Systems, which is supported by the NSF’s Materials Research Science and Engineering Centers Program DMR- 1420570. N.V. acknowledges the support of the Cluster of Excellence Engineering of Advanced Materials (EAM) and of the Interdisciplinary Center for Functional Particle Systems (FPS) at Friedrich-Alexander University Erlangen-Nürnberg. The authors would like to thank Orad Reshef, Alexander Tesler, Alison Grinthal, Anna Shneidman, and Peter Korevaar for helpful discussions. G.T.E., N.V., and J.A. designed research. C.R. and E.S. synthesized nanoparticles. G.T.E., C.R., T.K., and E.S. fabricated samples. G.T.E. and C.R. measured samples. G.T.E. performed calculations. G.E., N.V., and J.A. wrote the manuscript. All the authors discussed and reviewed the manuscript.