Researchers at the Tokyo Institute of Technology have successfully created a material that can absorb virtually all light that the human eye can see. And they used a lotus leaf to do it.
Metamaterials, by definition, are manmade. There is no hard and fast boundary between a metamaterial and any other synthetic material, but the defining characteristic of a metamaterial is that it is engineered to have properties that are rarely or never seen in nature. The new Tokyo material is different: it was inspired by the much-revered lotus leaf. That's why the researchers are coining a new term, the "biometamaterial."
It's a mouthful, but it's apt. The lotus leaf is the perfect template because of the unique way its cells are patterned on the surface of the leaf, where it gathers sunlight. The cilia (hairlike structures) on the leaves seemed to be structured in such a way as to absorb light effectively.
To mimic the structure, the researchers sprayed a very fine liquid gold on the leaf, which adhered to it like papier mâché. The resulting gold surface was incredibly thin: just 10 nm, about 1/100,000th of a millimeter at the smallest.
The unprecedented material absorbed nearly all light in the visible spectrum, meaning that it reflected virtually nothing. The researchers concluded that the rodlike structures of cilia on the original leaf were indeed the key to the unparalleled light absorption. The next step is to separate the gold from the leaf, which they haven't quite figured out yet, but they are working on various chemical processes to pry their new material off the lotus leaf so that it can then be created on its own, using the new material as a template.
The researchers have not yet said what they hope the biometamaterial will be used for, but similar surfaces that absorb most visible light are used in telescopes (to block out "light noise" and unwanted reflections) and solar panels.
The new discovery is detailed in an article titled, "Biometamaterials: Black Ultrathin Gold Film Fabricated on Lotus Leaf," in the journal Nature.