Controlling plasmonic resonances in binary metallic nanostructures

Investigation on the interplay of plasmonic resonances in binary nanostructures indicated that, at a fixed wavelength, with a variation in the difference permittivity ratio eta=(epsilon(2)-epsilon(0)/epsilon(1)-epsilon(0)), resonances exhibit the dielectric effect, resonance chaos, collective resonance, resonance flat, and new branch regions. This means that plasmonic resonances can be controlled by material parameters epsilon(1) and epsilon(2). In this work, using the Green's matrix method of solving the surface plasmon resonances, we first study the resonance combination of symmetrical binary three-nanostrip systems. Several resonance branches extend across the above mentioned regions. Near fields within the gaps and at the ends of nanostrips are greatly enhanced due to the influence of neighboring metallic material. Then, along each resonance branch, resonances in the dielectric permittivity region are mapped into the wavelength region of gold. Through adjusting material parameters epsilon(1) and epsilon(2), the resonance wavelength is tuned from lambda(R)=500 to 1500 nm, while for a single nanostrip it is only at lambda(R)=630 nm. We also find that comparable permittivity parameters epsilon(1) (or epsilon(2)) and epsilon(Au)(omega) can control resonance wavelength and intensity effectively. High dielectric permittivity of the neighboring metal has also an advantage in a giant enhancement of the near field. These findings provide new insights into design of hybrid plasmonic devices as plasmonic sensors. (C) 2010 American Institute of Physics. [doi:10.1063/1.3407527]