An Ingenious Super Light Trapping Surface Templated from Butterfly Wing Scales

Abstract

Based on the super light trapping property of butterfly Trogonoptera brookiana wings, the SiO2 replica of this bionic functional surface was successfully synthesized using a simple and highly effective synthesis method combining a sol-gel process and subsequent selective etching. Firstly, the reflectivity of butterfly wing scales was carefully examined. It was found that the whole reflectance spectroscopy of the butterfly wings showed a lower level (less than 10 %) in the visible spectrum. Thus, it was confirmed that the butterfly wings possessed a super light trapping effect. Afterwards, the morphologies and detailed architectures of the butterfly wing scales were carefully investigated using the ultra-depth three-dimensional (3D) microscope and field emission scanning electronic microscopy (FESEM). It was composed by the parallel ridges and quasi-honeycomb-like structure between them. Based on the biological properties and function above, an exact SiO2 negative replica was fabricated through a synthesis method combining a sol-gel process and subsequent selective etching. At last, the comparative analysis of morphology feature size and the reflectance spectroscopy between the SiO2 negative replica and the flat plate was conducted. It could be concluded that the SiO2 negative replica inherited not only the original super light trapping architectures, but also the super light trapping characteristics of bio-template. This work may open up an avenue for the design and fabrication of super light trapping materials and encourage people to look for more super light trapping architectures in nature.

Fig. 1

The macroscopic morphology of the butterfly wings and the reflectance spectroscopy of black and green region of the butterfly wings. a Photograph of butterfly Trogonoptera brookiana. b Optical microscopic image of the black butterfly wing scales. c The lower reflectance of the black wing scales was confirmed in the entire wave range

Fig. 2

FESEM images of original butterfly scales in the black region with different magnifications. a Lower magnification image. It was found clearly that these scales ranged in good order on the substrate. b, c Medium magnification image. This surface of the scale comprised a set of raised longitudinal quasi-parallel lamellae (ridges), the space between which was filled with a quasi-honeycomb-like structure. d The high-magnification images of the quasi-honeycomb-like structure

Fig. 3

Fabrication process from the original templates of butterfly wings to the SiO₂ negative replica. a 3D nanostructured model of the original butterfly wings. b The precursor solution filled the space left between the micro-ridges with a micropipettor. c The precursor solution became solidified through heating process. d The solid negative replica was obtained after the original bio-templates were etched away and cooled at room temperature

Fig. 4

FESEM images and EDS spectrum of the SiO₂ negative replica. a Lower magnification image. It could be found that the scales were still arranged in rows. However, they were no longer overlapped with each other. b Medium magnification image of the SiO₂ negative replica. It can be observed that notches are lying in parallel, with humps of different shapes between them. c High-magnification images of the replica surface. The sizes and shapes of the humps were in conformity with those of the pores shown in Fig. 2c. d The EDS spectrum showed the main elements constituting the SiO₂ negative replicas. e, f The scanning maps of silicon and oxygenium demonstrated the distribution of silicon and oxygenium, which was consistent with the structures shape of the subwavelength antireflective nanoditches arrays

Fig. 5

Schematic illustration of the multiple reflection and refraction occurred in the SiO₂ negative replicas and the reflectance spectroscopy analysis of the SiO₂ negative replica. a After multiple reflections and refractions, incident light traveled for a longer distance, and only a small part of the solar energy was reflected back to the air. b The average reflection of the SiO₂ negative replicas was about 20 % which was just 1/4 of the reflection of the flat plate without the negative quasi-honeycomb-like structure