Lotus Leaf-Based Metamaterial Capable of Near-Total Light Absorption

An experimental biometamaterial fabricated using a lotus leaf as a template is capable of almost total absorption of light across the entire visible spectrum.

Researchers from the Tokyo and Shibaura institutes of technology in Japan hypothesized that the unique structure of the leaf's surface — where cilia form tiny, randomly-orientated, macaroni-like nanorods, each measuring around 100 nm — might confine light effectively.

A lotus flower, top, lotus leaf, middle, and scanning electron microscope image of lotus leaf, bottom. Courtesy of the Tokyo Institute of Technology.

Using a spray sputtering technique, they applied a gold coating ranging in thickness from 10 nm to 30 nm on different samples. In addition to lotus leaves, they used leaves from three other plants as controls.

The researchers found that the 10 nm-thick gold biometamaterial created using lotus leaves exhibited reflectivity of less than 0.01 through the whole visible spectrum. The low reflectivity results in almost complete absorption of light on the material's surface. Finite-difference time-domain calculations suggest the low reflectivity is a result of the random orientation of nanorods on the leaf's surface.

Work is in progress to find an effective way to remove the gold biometamaterial from the leaf template once it is created. The researchers are considering a form of chemical treatment to that end.

Nanostructured surfaces that absorb virtually all visible light are used in telescopes to stop unwanted reflections and could be useful in photovoltaics.

The research was published in Scientific Reports (doi: 10.1038/ srep15992).