Credit: © 2008 ACS

When electrons near the surface of a material oscillate in unison, they form electromagnetic waves called plasmons. Plasmons have potential for remote sensing, imaging, lithography and even cancer treatment, but they can be difficult to manipulate. Now, Xiang Zhang and co-workers1 at the University of California and Lawrence Berkeley National Laboratory have demonstrated a simple way of controlling plasmons using patterns cut into a thin metal film.

The researchers show that light from a mercury lamp can be converted into surface plasmons if it hits a sharp edge or slit in a material. This process diffracts the light into plasmons with a broad band of frequencies — plasmons generated in different places can interfere in any number of ways.

By cutting nanoscale slits in aluminium films — in patterns including triangles, squares and pentagons — the researchers demonstrated several different plasmon interference patterns. The plasmon patterns can be further tailored by adjusting the wavelength, polarisation or incident angle of the light beam.

This accurate control of plasmons could lead to new methods of particle manipulation. It could also be used for 'sub-wavelength' imaging, because the plasmon interference patterns resolve features even smaller than the wavelength of the original light beam.