Plasmonic response of electrically connected dimers shows new resonant mode
Plasmonic response of electrically connected dimers shows new resonant mode lead image
Existing work on plasmonic devices has so far addressed only resonances of stand-alone nanoantennas. In the Journal of Applied Physics, researchers report finding that electrically connecting dimers in an array, and changing the shape and distance between connections, impacted the resonance behavior significantly. Understanding these kinds of effects could improve future nanoantenna designs to eventually make optical rectifying antennas (rectennas) a viable tool for energy harvesting.
The dominant dipole response of a dimer antenna depends on properties of the system such as length, material, and gap between electrodes, which give stand-alone dimer antennas a certain well-defined resonant behavior. The new findings show that in making connections between dimers, the response differs, which could be expected but is largely unexplored. For example, changing the gap has a much smaller effect on the dipole response than in unconnected devices.
After discovering an additional resonant mode in simulations, the authors built homodimer arrays, the symmetric versions of the two-part antenna arrays, and anti-symmetric heterodimer arrays from of gold deposited on silica. To extract signals from these nanoantennas, the individual dimers were connected by wires. They tested the effects of adding these “busbars,” the interconnecting gold nanowires, on the resonance responses.
The heterodimers consist of a triangular shaped electrode and a flat surface electrode facing the triangular electrode’s sharpest point, where the electric field is most strongly enhanced. When this apex comes close enough to the surface, a rectified current may result from light incident on the antenna.
The busbars generate their own charge-oscillation modes, which change the resonant behavior of the entire array. This additional resonance could expand the portion of the spectrum that can activate nanoantennas. Depending on where the busbars connect to the nanoantennas, the new mode can be far more intense than the stand-alone resonances. This more complex resonance behavior of the array could enable optimized nanoantenna array circuits for energy harvesting or optical sensing.
Source: “Optical properties of electrically connected plasmonic nanoantenna dimer arrays,” by Darin T. Zimmerman, Benjamin D. Borst, Cassandra J. Carrick, Joseph M. Lent, Raymond A. Wambold, Gary J. Weisel, and Brian G. Willis, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5008511 .
