Now scientists are working on metallic nanoparticles to manipulate light in more effective ways than conventional optical materials to tap extra energy from the sunlight. Rice University researchers are paying attention to cup-shaped gold nanostructures that can bend light in a more manipulative manner. Here the cup behaves like three-dimensional nano-antennas.
The gold nanocups interrelate with light in two major ways: axially, the up-down direction, or transverse, the left-right track. The transverse mode is by far the more powerful of the two. Rice University researcher, Naomi Halas, who is also the study’s corresponding scientist, said, “When we illuminated the nanocups, the transverse interaction exhibited a strong scattering resonance.” She is working on this project with colleague Nikolay Mirin. She explained further, “We learned that the direction of the transverse resonant light scattering depends on the orientation of the cups, a property that has not been observed in studies of similar structures.”
Man-made “metamaterials” have an edge over naturally occurring materials. They can cause dramatic physical effect with the interaction of light. These “metamaterials” have very fine structures with features smaller than the wavelength of light. Features of “metamaterials” can pass on unique and fascinating optical behaviors. Hence scientists are naturally interested in “metamaterials” because of their interaction with light that naturally occurring materials are unable to show.
Naomi Halas has developed a material that collects light from any direction and emits it in a single direction. The material uses very tiny, cup-shaped particles called nanocups.
Mirin produced thin layers of gold deposited from various angles onto polystyrene or latex nanoparticles. These had been allocated haphazardly on a glass substrate. The cups that formed around the particles – and the dielectric particles themselves – were locked into an elastomer and lifted off of the substrate. “You end up with this transparent thing with structures all oriented the same way,” he said. In short, Mirin had a metamaterial that derives its properties from its structure and the composition is not playing an important role in it. The most important aspect of this substance is it captures light from any direction and focuses it in a single direction. According to Mirin, its greatest advantage is, “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.”
Mirin had been working on this concept earlier. He was trying to make a thin gold film with nano-sized holes. But later on he realized that the knocked-out bits were worth investigating. Previous work on gold nanocups reveled to scientists a sense of their properties, but until Mirin’s disclosure, no one was able to lock ensembles of isolated nanocups to safeguard their matching orientation. Naomi Halas, also affirmed, “The big breakthrough here was being able to lift the nanocups off of a structure and preserve their orientation. Then we could look specifically at the properties of these oriented nanostructures.”
Nanocup ensembles can focus light in a precise direction no matter where the incident light is coming. This factor can be used to its greatest advantage in thermal solar power. Capitalizing on this property, lots of money can be saved which is being spent on machinery. Because here a solar panel doesn’t have to track the sun yet focuses light into a beam that’s always on target! Halas also said that utilizing nanocup metamaterial to pass on optical signals between computer chips has potential, and enhanced spectroscopy and superlenses are also viable possibilities.
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