Plasmonic graphene controls rippling electrons

As if diamond-beating strength and high conductivity aren't enough, graphene has a new trick: turning electron waves on and off. That could make this wonder material a useful component in novel types of circuits, exotic materials and ultra-sharp microscopes.

When light hits some materials in just the right way, ripples of electrons called plasmons appear on the surface. These rippling surfaces can focus light through openings smaller than light's wavelength, so might allow microscopes with unprecedented resolution.

For decades, researchers have focused on metals as the best material for carrying plasmons. They have the advantage of being abundant in free electrons, but their plasmons were hard to control without building delicate nanostructures.

Now, two teams have shown that plasmons can be produced in graphene too, a substance made of atom-thin layers of carbon that is prized for its ability to conduct electricity better than copper or gold, and its impressive strength.

Plasmon switch

Both groups coated a thin silicon wafer with a layer of graphene, and excited the surface with a laser. They used a nanoscale microscope to image the resulting electron ripples. Unlike similar work in metals, both teams were able to control their graphene plasmons, using a voltage to make the ripples grow and shrink.

"We can basically turn plasmons on and off, something you cannot do with metals," says Dmitri Basov of the University of California, San Diego, who led one of the teams.

As well as microscopes, the ability to switch plasmons could be useful when building circuits and also metamaterials, which can bend light around objects by controlling its path. Metamaterials are the technology behind preliminary invisibility cloaks but must be intricately engineered. Plasmonic graphene might be capable of the same feat but would be easier to manufacture.

Journal references: Nature, DOI: 10.1038/nature11253 and 10.1038/nature11254

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