Asymmetric Structural Colors Based on Monodisperse Single Crystal Cu2O spheres
The structural color has attracted broad attention owing to its anti-photobleaching capability and brilliant metallic color. Especially, the asymmetric structural colors generated by a simple material will have great practical significance in the field of biomimetic materials, double-side display and anticounterfeiting. Asymmetric optical effect was usually achieved by the plasmonic effect of Ag or Au nanocrystals. Here, for the first time, we realized the asymmetric structural colors based on asymmetric scattering of Cu2O single crystal spheres. By spray-coating Cu2O spheres on glass slide, different structural colors were viewed from the Cu2O film side and the glass slide side. FDTD simulations confirmed that the asymmetric colors were ascribed to the inhomogeneous distribution of electric field intensity. The film built by 200 nm Cu2O spheres on glass slide shows green and cyan structural colors from the front and back side, respectively. The colors of both sides of the Cu2O films were proved to be tuned by changing the diameters of Cu2O single crystal spheres. Different substrates were used to examine the influence of substrates on the asymmetric colors. Finally, inspired by different brilliant colors from the front and back of nature creatures, the patterns of butterfly and petals were fabricated by Cu2O spheres. Impressively, similar with nature, the patterns show completely different colors viewed from the front and back sides. The asymmetric structural colors of Cu2O single crystals spheres will open a new avenue to realize multi-mode color output and pave its applications in display, biomimetic materials and anticounterfeiting materials.