Plasmon potential

Incident photons may induce a huge voltage in metal nanowires, bringing the possibility of nanoscale optical detection.

Credit: © 2009 APS

When photons strike a surface, they can exert forces on electrons to produce a detectable voltage. Mark Stockman and colleagues at Georgia State University have predicted that an enhanced version of this effect may occur when the electrons are confined within a metal nanowire, providing many potential light-sensing applications¹.

In a metal there are quasiparticles known as plasmons, which represent oscillations in the electron plasma. When a photon reaches the metal surface, it may couple to a plasmon to produce a surface plasmon polariton (SPP).

Stockman and colleagues calculated that when these SPPs are confined in a narrow wire they must exert a huge electromotive force on the metal electrons. They call this effect the giant surface-plasmon-induced drag-effect rectification, or SPIDER, and predict that it will increase rapidly in thinner nanowires. For example, nanowires just 5 nm in radius may support a SPIDER voltage as high as 10 volts, and huge electric fields would be generated at the metal surface.

The researchers suggest that tapered nanowires could be used to build versatile photodetectors with an extremely fast response time. The SPIDER effect could also enable spectroscopic analysis of nanosize chemical and biological objects — a task that was previously thought only possible with semiconductors.