Replicating nano structure of butterfly wings could lead to better solar cells

Researchers have developed a technique to replicate biological structures, such as butterfly wings, on a nano scale. They focused on the tiny nano-sized photonic structures that are found in the insects’ cuticle, and which give insects their iridescence - that slightly metallic sheen that also seems to shift in color depending on the viewing angle. By replicating the biotemplate of butterfly wings, the researchers hope to be able to make various optically-active structures, such as optical diffusers or coverings that maximize solar cell absorption.

The appearance of butterfly wings is the result of two fundamental mechanisms. The first is the presence of chemical pigments that absorb certain wavelengths of light and transmit or reflect others, which is referred to as the “chemical” color. The second is an iridescence produced by the interference of light, due to multiple reflections within the physical structure of the material, and is known as the “physical” or “structural” color. By replicating the structure responsible for iridescence, the researchers say they will be able to make all kinds of optically active structures.

The research team from Pennsylvania State University (PSU) and the Universidad Autónoma de Madrid (UAM) created copies of the nano structures of butterfly wings using compounds based on Germanium, Selenium and Stibium (GeSeSb) and employed a technique called Conformal-Evaporated-Film-by-Rotation (CEFR), which combines thermal evaporation and substrate rotation in a low-pressure chamber. They also used immersion in an aqueous orthophosphoric acid solution to dissolve the chitin (substance typically found in the exoskeleton of insects and other arthropods).

The methods used to date to replicate bio structures are very limited when it comes to obtaining effective copies on a nanometric scale, and they often damage the original biostructure because they are used in corrosive atmospheres or at high temperatures. The new technique "totally" overcomes these problems, as it is employed at room temperature and does not require the use of toxic substances.

"Furthermore, the technique can be used to replicate other biological structures, such as beetle shells or the compound eyes of flies, bees and wasps," says Raúl J. Martín-Palma, lecturer at the Department of Applied Physics of the UAM and co-author of the study.

The compound eyes of certain insects are sound candidates for a large number of applications as they provide great angular vision. "The development of miniature cameras and optical sensors based on these organs would make it possible for them to be installed in small spaces in cars, mobile telephones and displays, apart from having uses in areas such as medicine (the development of endoscopes) and security (surveillance)", Martín-Palma says.