Excitation dependent Fano-like interference effects in plasmonic silver nanorods

Abstract

Surface plasmon resonances in metal nanoparticles are an emerging technology platform for nano-optics applications from sensing to solar energy conversion. The electromagnetic near field associated with these resonances arises from modes determined by the shape, size, and composition of the metal nanoparticle. When coupled in the near field, multiple resonant modes can interact to give rise to interference effects offering fine control of both the spectral response and spatial distribution of fields near the particle. Here, we present an examination of experimental electron energy loss spectroscopy (EELS) of silver nanorod monomer surface plasmon modes and present an explanation of observed spatial amplitude modulation of the Fabry-Pérot resonance modes of these silver nanorods using electrodynamics simulations. For these simulations, we identify differences in spectral peak symmetry in light scattering and electron spectroscopies (EELS and cathodoluminescence) and analyze the distinct near-field responses of silver nanorods to plane-wave light and electron beam excitation in terms of a coupled oscillator model. Effects of properties of the material and the incident field are evaluated, and the spatially resolved EELS signals are shown to provide a signature for assessing Fano-like interference effects in silver nanorods. These findings outline key considerations and challenges for interpreting electron microscopy data on plasmonic nanoparticles for understanding nanoscale optics and for characterization and design of photonic devices.

Link between Cathodoluminescence and Electron Energy Loss Spectroscopy and the Radiative and Full Electromagnetic Local Density of States

“…Such spectral shifts have been experimentally measured recently 24. Furthermore, the CL and radiative EMLDOS resonances may be affected by the inter-mode coupled terms, which can lead to asymmetric line shapes while the EELS and full EMLDOS resonances remain Lorentzian.Previously, asymmetric CL line shapes as opposed to symmetric EELS line shapes have been pinpointed as Fano resonances in calculations on nanowires 32. Our analysis shows that these asymmetric line shapes are due to interferences between the far-field radiation from locally excited modes, which cancel out in the full energy transfers due to additional absorption contributions.…”

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 than around 100 nm, high order longitudinal modes can be probed both in EELS 22,32,36-38 and CL. 12,21,32,38,39 Figure 3 shows calculations of the z...…”

Self-hybridization within non-Hermitian localized plasmonic systems

“…2a,b, we calculate EELS spectra of as a function of L for a nanocross. When L is small, the cross eigenmodes have the same spatial profile as the well-known rod eigenmodes 35 , with eigenvectors σ n displaying periodic profiles with n nodes (Fig. 2c).…”

“…Using the convention of refs [32][33][34][35] , we call diabatic the eigenvectors of the unperturbed basis σ τ { , } m m (0) (0) in which M is expressed in equation (4), and adiabatic the eigenvectors of the hybridized basis σ τ…”

Freeform 3D Plasmonic Superstructures

“…Plasmonic nanoparticle clusters have attracted great attention due to the unique capability to manipulate electromagnetic elds at the sub-wavelength scale [1][2][3][4][5] . Ensembles of metallic nanoparticles generate various electromagnetisms at optical frequencies such as arti cial magnetism [6][7][8][9][10] and Fano-like interference [11][12][13] and a strong eld localization in the structure [14][15][16] . These unique properties are geometry-dependent and lead to a broad range of applications in sensing 16,17 , surface-enhanced spectroscopies [18][19][20][21][22] , nonlinear integrated photonics 23,24 , and light harvesting 25,26 .…”