Keywords:Nanoantennas, Plasmons, Directional light scattering
Nanoantennas can efficiently convert light signals between near- and far-field. They are of importance in spectroscopy, detection, photonic circuits, and solar energy harvesting. Owing to their extremely large absorption/scattering cross-sections and strong capability in confining light at nanoscale, plasmonic nanostructures are excellent candidates for creating nanoantennas. We have developed a chemical method for the growth of monodisperse silver nanorods with both excellent length and diameter control. When the lengths of silver nanorods are in the range of ~150–550 nm, well-controlled, higher-order longitudinal plasmon modes are observed. These silver nanorods can act as broadside nanoantennas when deposited on high-refractive-index substrates, where light is scattered along the two side directions instead of at the two ends. Moreover, silver nanorods also exhibit a color-routing behavior. Depending on the length, silver nanorods scatter light of different colors along different directions. When silver nanorods are grown even longer, they can function as nanoantennas for surface-enhanced infrared absorption.