Gold nanocups at their magnetoinductive resonance have the unique ability to redirect scattered light in a direction dependent on cup orientation, as a true three-dimensional nanoantenna.
Nanocups are just what they sound like: very tiny, cup-shaped particles. What makes them special is their ability to bend light. Halas and Mirin have found a way to make material incorporating nanocups that can bend light in a specific direction.
Redirecting scattered light means none of it bounces off the metamaterial back into the eye of an observer. That essentially makes the material invisible. "Ideally, one should see exactly what is behind an object," said Mirin.
"The material should not only retransmit the color and brightness of what is behind, like squid or chameleons do, but also bend the light around, preserving the original phase information of the signal."
Halas said the embedded nanocups are the first true three-dimensional nano-antennas, and their light-bending properties are made possible by plasmons.
Using nanocup metamaterial to transmit optical signals between computer chips has potential, she said, and enhanced spectroscopy and superlenses are also viable possibilities.
A solar panel that doesn't have to track the sun yet focuses light into a beam that's always on target would save a lot of money on machinery.
Solar-generated power of all kinds would benefit, said Halas. "In solar cells, about 80 percent of the light passes right through the device. And there's a huge amount of interest in making cells as thin as possible for many reasons."
Halas said the thinner a cell gets, the more transparent it becomes. "So ways in which you can divert light into the active region of the device can be very useful. That's a direction that needs to be pursued," she said.
To make light-bending material, the Rice researchers spread polystyrene or latex colloidal particles on a glass slide, evaporate a layer of gold at various angles on top of the particles, deposit a layer of elastomer on top and then, after curing, lift the slab from the substrate with the oriented nanocups embedded.