Abstract
A Fano resonance is experimentally observed in a single silver nanocube separated from a supporting silver film by a thin aluminum oxide film. The resonance spectrum is modulated by changing the size of the silver nanocube and its distance from the silver film. The system is fabricated by a bottom-up process with an accurately controlled nanogap at the sub-6-nm scale. The simulation result shows that the destructive interference between the dipole mode and the quadrupole mode in this “nanocube on mirror” (NCoM) structure is responsible for the resonance. The spectra red-shifted as the size of the silver nanocube increased and its distance from the silver film decreased. In addition, a refractive index sensitivity of the spectrum of 140 meV/RIU (refractive index unit), with a 2.4 figure of merit, is obtained by changing the dielectric environment around the silver nanocube. This work will enable the development of high-performance tunable optical nanodevices based on NCoM structures.
Highlights
When discrete and continuous excited-state energy levels overlap, quantum interference occurs.A zero absorption occurs in a specific optical band, and thereby generates an asymmetric spectrum that is called a Fano resonance [1]
The destructive interference suppresses the radiation attenuation of the system, which greatly increases its sensitivity to the surrounding media and concentrates the system energy on the surface of the structure [2]
It consists of a single silver nanocube and a silver film
Summary
When discrete and continuous excited-state energy levels overlap, quantum interference occurs. Sci. 2020, 10, 2603 structures, there are abundant plasmon hybridizations among various plasmon modes that lead to Fano resonances, such as a disk-ring nanocavity [19], a metal core-shell nanostructure [20,21,22], a self-assembled metal nanostructure [6,14,23,24], a metal nanoparticle (NP) array [25,26,27,28], and a waveguide and cavity resonator coupling structure [29,30] These complex structures usually require complicated fabrication methods. The refractive index sensitivity of the Fano resonance spectrum in the NCoM structure is investigated by varying the dielectric environment around the silver nanocube
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