Butterfly wing inspired mimicry of optical nanotechnology

Our technologies for transmitting, manipulating and displaying information, whether for work or play, depend increasingly on our ability to control light; to harness and transform colour.

Some of nature's most beautiful creatures depend on such a facility too, and often they show us that beauty can be inextricably linked to utility.

Therefore, inspired by the butterfly structures, Professor Min Gu from the School of Science teamed up with researchers from Swinburne University of Technology to use optical two-beam super-resolution lithography to create gyroid structures that are inherently 3D and which are also mechanically stronger than natural gyroids.

Butterfly wings are made of a hard material called chitin and in some iridescent butterfly wings this is made in a gyroid pattern which means it is designed as a 3D periodic structure made up of an intertwining and curved surface.

The research team succeeded in making photonic gyroid nanostructures similar to those found in butterfly wings using optical two-beam super-resolution lithography.

The artificial structures, which outperform their natural counterpart in many ways, offer inspiration to engineers seeking to control light in photonic and optical technologies, and could lead to more brilliant visual displays, new chemical sensors, and better storage, transmission and processing of information.

Until now, however, the techniques employed to make such structures were typically low-resolution and were thus unable to produce artificial gyroid structures with lattice constants comparable to those found in the butterfly wings.

Gu explained that the structures have a lattice constant of 360 nm and a Young’s Modulus that is up to 20% higher than their biological counterparts.

"The artificial materials also boast long-range periodicities and well-defined crystalline boundaries, unlike their natural counterparts that suffer from uncontrolled structural disorders," he said.

"In addition, the artificial gyroids produced have the same blue-green colour as the butterfly Callophrys rubi’s wings and have chiral properties lacking in the imperfect natural structure.

"For instance, they contain only left- or right-handed single gyroid chiral molecules that are mirror images of one another, while the natural version contains a mixture of both.

"This means that the artificial architecture is much more suitable for applications, such as photonic crystals with optical bandgaps, and miniature chiral beam splitters."

First author Dr Zongsong Gan from Swinburne University of Technology further explained that metamaterials made from the artificial gyroid should also have tuneable nonlinear optical properties and respond to light at ultrafast speeds, making them ideal for high-speed switches.

"Compared to conventional fabrication techniques for gyroids and other such structures, optical two-beam super-resolution lithography, which is rather like direct laser writing, has two significant advantages," Gan said.

"The first is that it has improved resolution and the second is that the materials fabricated with this technique have better mechanical strength.

"Apart from applications in biomimetic photonics, the new gyroid structures could help make more compact optoelectronics because, thanks to their smaller size, larger numbers of devices can be integrated onto a single chip.

"However, for 3D devices, smaller and more compact also means that there is a higher risk of the structure collapsing because it is mechanically weaker than an equivalent 2D sheet.

"Our fabrication technique allows us to make stronger architectures and so overcome this problem."

The research findings were published in the journal Science Advances entitled Biomimetic gyroid nanostructures exceeding their natural origins.

Professor Gu is the Associate Deputy Vice-Chancellor Research Innovation and Entrepreneurship, RMIT Distinguished Professor and Director, Laboratory of Artificial-Intelligence Nanophotonics.

He is also the sole author of two standard reference books and has over 500 publications in nano/biophotonics and his work has been cited over 14,100 times.

In 2015 he was awarded the Australian Institute of Physics Walter Boas Medal for his original research and contributions to physics.

Story: Petra van Nieuwenhoven