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MIT Technology Review

Waves of Electrons

Surface plasmons could improve solar cells and wireless devices.

October 20, 2008

Photons–particles of light–are good at carrying energy and information through space; electrons aren’t, but they’re easier to control. Many modern technolo­gies–imaging systems, solar cells, information networks–need to mediate between footloose photons and well-behaved electrons, but getting the particles to interact with each other can be a challenge.

T-Ray filter: Terahertz radiation causes waves to propagate through electrons in a metal sheet. Where the waves bend around holes in the sheet, the resulting electric field causes the emission of terahertz radiation at a single frequency. That could allow different frequencies to be encoded with different information, increasing capacity in a wireless network.

Recently, researchers trying to bridge the photon-­electron divide have been turning to a peculiar physical entity called a surface plasmon, which is like a wave passing through the cloud of electrons on the surface of a metal. Phenomena such as light shining on a sheet of metal induce plasmons, much the way dropping a stone in a pond induces waves. The shape and motion of the waves depend on characteristics of the metal–which could be, say, an ultrathin, perforated sheet or a nanosphere. Below is a sampling of research projects that seek to take advantage of the plasmon’s versatility.