Ridge/hole Hierarchical Super Black Amorphous Carbon Architecture Inspired By Black Butterfly Wings

It has been a long story seeking for super black materials with goodabsorption (>99%) and low reflectance (<1%) to reduce unnecessaryreflection that can severely limit the performance of optical devices, sinceKirchhoff introduced the concept of blackbody and Planck discovered thelaw of blackbody radiation over a hundred years ago. Carbon Nanotubeswith refractive index close to air and materials with Graded-indexstructures, such as black silicon, Ni-P alloy and black gold, are widely usedto decrease reflection. During millions of years’ evolution, nature has alsoneeded and finally got elaborate nanostructures to achieve low reflection,and some butterflies’ blackness can be considered structurally-assisted.Super black amorphous carbon architecture can be obtained by integratingthe antireflection nanostructures in black butterfly wings and amorphouscarbon with broadband absorption, which can also provide inspiration andguidance for design and fabrication of super black materials.Inspired by the antireflection nanostructures of inverse V-type ridgesand double row rectangular nano hole arrays in black wings of the butterflyTroides aeacus, we find and demonstrate a new ridge/hole hierarchical superblack amorphous carbon architecture. The architecture was structurallycharacterized with scanning electron microscope, and the chemicalcomposition was analyzed with Raman spectra, and reflection andtransmission spectra were measured with spectrophotometer.3D FDTDmodels were built with optiFDTD, and after calculation, simulatedreflectance, transmittance as well as Poynting Vector maps were acquired,through which we can analyze the effect of each structural component onantireflection. Both experimental results and theoretical simulation show that the architecture has much lower reflection than flat substrate and glassycarbon, which can be attributed to the hierarchical nanostructures. As thesintering temperature going up, the architecture’s reflectance increases fromaround0.6%(500oC) to about1%(800oC), and transmittance decreasesfrom around0.005%(500oC) to about0.001%(800oC) in visible light(380~795nm), which can be ascribed to the enhancement of graphitizationdegree and size parameters’ shrinkage. Poynting vector maps show thatridges primarily reflect incident light into nano hole regions, which play adominant role in antireflection process. The holes with ribs around them actas waveguides for light with shorter wavelengths, while changing to abarrier for longer wavelengths.The work provides new inspiration for super black materials appliedin optical instruments, detectors and solar conversion devices. With precisemodel and dimensions, the ridge/hole as well as previous inverse V-typeridge architecture can be obtained through methods such as sputtering orevaporating target matrials on proper substrates, nano imprintinglithographyand reactive ion etching. As a fantastic example of integratingelaborate architectures engineered by Nature and existing appropriatematerials, it encourages human beings to explore more wonderfulhierarchical structures in Nature, and furthermore to extract prototypes forreferring to and borrowing, to resolve thorny scientific problems lying onthe way ahead.