Technology could allow ultra-potent microscopes, new electronic devices

While developing new types of lenses, researchers have crafted a layered material that makes light bend in a way nature never intended.

Light naturally bends, or refracts, in a specific way when it travels from one material to another. This creates, for example, the illusion of a drinking straw looking bent when placed in water.


Negative refraction compared to natural refraction. In natural refraction, light going from one material to another bends in some direction to the opposite side of the "normal," an imaginary line perpendicular to the surfaces. In negative refraction, light bends back from the normal.

But the new material, crafted from alternating layers of semiconductors, refracts light backwards—a phenomenon called negative refraction, researchers say.

Negatively refracting materials have been made before. But this is the first that’s fully three-dimension and made totally of semiconductors, the investigators said. Semiconductors are substances that can switch between electrically conducting and non-conducting states, which makes them key components of electronic devices.

The negative-refraction semiconductor structure could be useful in instruments such as chemical threat sensors, communications equipment and diagnostics tools, the scientists said. Semiconductors “are extremely functional materials. These are the things from which true applications are made,” said engineer Claire Gmachl of Princeton University in New Jersey, one of the researchers.

Natural refraction is why lenses have to be curved, a trait that limits image resolution. The new material makes flat lenses possible, Gmachl and colleagues said—theoretically allowing for the creation of microscopes that can focus on objects as small as DNA strands.

A limitation of the new material, though, is that it works only with infrared light, a type of light with slightly lower energy than the visible. But the researchers said they hope the technology will expand to other wavelengths in the future.

The substance is in a class of materials called metamaterials, made of traditional substances, such as metals or semiconductors, arranged in very small alternating patterns that modify their collective properties. This enables metamaterials to manipulate light in ways that normal materials cannot. Scientists are also investigating the possibility that certain metamaterials could form invisibility cloaks.

The refraction findings, by a team led by Princeton engineering graduate student Anthony Hoffman, appeared in the Oct. 14 online issue of the research journal Nature Materials.

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