Researchers have succeeded in mapping how light behaves in complex photonic materials inspired by nature, like iridescent butterfly wings. Scientists have broken the limit of light resolution at the nanoscale and delivered a fundamental insight into how light and matter interact, which could lead to the development of enhanced bio-sensors for healthcare and more efficient solar cells and displays.

Optical measurements of light waves at the nanoscale have always been limited by the resolution of the optical microscope, but researchers were able to break this limit using a new technique which combines electronic excitation and optical detection, to explore the inside of a photonic crystal and study the confinement of light. Working with a spatial resolution of 30 nanometers, scientists examined the structures at a resolution more than ten times smaller than the diffraction limit for light, revealing a greater understanding of how light interacts with matter to create, for example, the visible iridescence phenomena observed in nature on the wings of butterflies.

The team constructed an artificial two-dimensional photonic crystal by etching a hexagonal pattern of holes in a very thin silicon nitride membrane. Photonic crystals are nanostructures in which two materials with different refractive indices are arranged in a regular pattern, giving rise to exotic optical properties. Natural photonic crystals can be found in certain species of butterflies, birds and beetles as well as in opal gemstones where they give rise to beautiful shimmering colours.
The photonic crystal inhibits light propagation for certain colours of light, which leads to strong reflection of those colours, as observed when such materials ‘catch the light’. By leaving out one hole, a very small cavity can be defined where the surrounding crystal acts as a mirror for the light, making it possible to strongly confine it within a so-called ‘crystal defect cavity’.
The scientists based their research methods on a technique used in geology, called cathodoluminescence, whereby a beam of electrons is generated by an electron gun and impacted on a luminescent material, causing the material to emit visible light.

With major advances in nanofabrication techniques it has become possible to construct artificial photonic crystals with optical properties that can be accurately engineered. These structures can be used to make high-quality nanoscale optical waveguides and cavities, which are important in telecommunication and sensing applications.

This story is reprinted from material from King's College London, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.