Huge electric field enhancement and highly sensitive sensing based on the Fano resonance effect in an asymmetric nanorod pair

Abstract

A sharp plasmonic Fano resonance is found to appear in a silver nanorod pair structure with broken length symmetry. It is shown that it arises from strong interference between a narrow plasmon mode of inter-nanorod near-field coupling and broad scattering from the nanorod. The inter-nanorod coupling is the result of the magnetic dipole plasmon resonance induced by the anti-parallel current of the nanorod pair, while the broad scattering is caused by electric dipole oscillation. The numerical results show that a giant local field enhancement (197), a high quality factor (52) and a sensing sensitivity of 1426 nm per refractive index unit in the symmetry-broken nanorod pair with a displacement Δl = 40 nm originated from a pronounced Fano resonance in the near-infrared spectrum. Huge local field enhancement and high sensitivity make this simple structure promising for surface enhanced Raman spectroscopy and sensing applications.