Sep 19, 2007
Plasmonics forges ahead
Physicists in Ireland and Germany have developed a new tunable nanoscale structure based on nanowires embedded in a flexible polymer substrate. The breakthrough device will allow researchers to advance from classically restricted systems into the new quantum realm of tunable surface plasmon polaritons, important for a variety of applications in photonics.
The tunable structures are crucial for further research in a field known as plasmonics – a new branch of photonics. The practical uses of surface polariton plasmons (SPPs) extend to the development of novel spectroscopic techniques for use in the life sciences, such as Surface Plasmon Resonance, ultra-sensitive methods from Surface Enhanced Raman Scattering to subwavelength optics, as well as for the fundamental understanding of quantum behaviour at nano and meso-scales.
SPPs are quasiparticles and are quantum phenomena that arise from the interaction of light with a metal's conduction electrons. Plasmon polaritons are part light and part electron wave and possess new properties not seen in either photons or excitons. In conjunction with metallic and metallodielectric nanostructures, SPPs are alternatives to planar waveguides and photonic crystal structures for strongly guiding and manipulating light. Planar waveguides and photonic crystals are widely studied as key components for future integrated photonic devices with structural elements smaller than the wavelength of light.
Now, Dominic Zerulla of University College Dublin and colleagues at several institutions in Germany have made a novel device that allows them to choose the properties of excited SPPs. It consists of a periodic arrangement of metallic ribbon-like quantum wires on a tunable elastic polymer substrate. The beauty of the structure is that its periodicity can be tuned over a wide range of wavelengths and angle of incidences of light.
"In classical experiments the desired excitation of SPPs by photons is naturally restricted to specific optical setups that confine and limit the experiment to a unique combination of photon wavelength and angle of incidence according to the 'SPP dispersion relation'," Zerulla told nanotechweb.org. "By implementing these tunable quantum wire materials, we are the first to successfully excite SPPs on such a structure with the important advantage of variable periodicity."
Apart from important applications in optics, the device will allow crucial fundamental questions about these quasiparticles to be answered. These include their localization, higher order excitation, lifetime and group velocity.
The researchers were able to make their device by using a non-rigid polymer as a substrate, rather than the traditional metal, glass or semiconductor materials. This allows the distances between the embedded nanowires to be tuned by simple mechanical stretching.
The system may even be used as the basis of a new spectroscopic technique or plasmonic biosensor in the future, adds Zerulla.
The team says that it is now ready to publish new results on the transition from a propagating SPP mode to a localized standing wave pattern. The present study was reported in Physical Review B.
About the author
Belle Dumé is contributing editor at nanotechweb.org