Abstract
We theoretically study plasmonic antennas featuring areas of extremely concentrated electric or magnetic field, known as hot spots. We combine two types of electric-magnetic complementarity to increase the degree of freedom for the design of the antennas: bow-tie and diabolo duality and Babinet's principle. We evaluate the figures of merit for different plasmon-enhanced optical spectroscopy methods: field enhancement, decay rate enhancement, and quality factor of the plasmon resonances. The role of Babinet's principle in interchanging electric and magnetic field hot spots and its consequences for practical antenna design are discussed. In particular, diabolo antennas exhibit slightly better performance than bow-ties in terms of larger field enhancement and larger Q factor. For specific resonance frequency, diabolo antennas are considerably smaller than bow-ties which makes them favourable for the integration into more complex devices but also makes their fabrication more demanding in terms of spatial resolution. Finally, we propose Babinet-type dimer antenna featuring electromagnetic hot spot with both the electric and magnetic field components treated on equal footing.
Highlights
Plasmonic antennas (PAs) are metallic particles widely studied for their ability to control, enhance, and concentrate electromagnetic field [1]
The hot spots typically arise from the interaction between adjacent parts of a plasmonic antenna separated by a small gap [2,3] but they can be based on the lightning rod effect [4,5,6] or combination of both
We perform a comprehensive study on the plasmonic antennas featuring electric, magnetic, and electromagnetic hot spots: bowtie and inverted diabolo, diabolo and inverted bowtie, and their dimers, respectively
Summary
Plasmonic antennas (PAs) are metallic particles widely studied for their ability to control, enhance, and concentrate electromagnetic field [1]. Focusing of the field stems from the excitation of localized surface plasmons (LSP)—quantized oscillations of the free electron gas in the metal coupled to the evanescent electromagnetic wave propagating along the boundary of the metal. In judiciously designed plasmonic antennas, local spots of enhanced electric or magnetic field can be formed, referred to as hot spots. Electromagnetic hot spots with simultaneous enhancement of both electric and magnetic field are unique for plasmonic antennas [13]. Their formation has been observed in dielectric resonators (silicon nanodimers) [14]
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