Cathodoluminescence as a probe of the optical properties of resonant apertures in a metallic film

Abstract

Here we present the results of an investigation of resonances of azimuthal trimer arrangements of rectangular slots in a gold film on a glass substrate using cathodoluminescence (CL) as a probe. The variation in the CL signal collected from specific locations on the sample as a function of wavelength and the spatial dependence of emission into different wavelength bands provides considerable insight into the resonant modes, particularly sub-radiant modes, of these apertures. By comparing our experimental results with electromagnetic simulations we are able to identify a Fabry–Pérot mode of these cavities as well as resonances associated with the excitation of surface plasmon polaritons on the air–gold boundary. We obtain evidence for the excitation of dark (also known as sub-radiant) modes of apertures and aperture ensembles.

Mapping Local Surface Plasmon Modes in a Nanoplasmonic Trimer Using Cathodoluminescence in the Scanning Electron Microscope

“…The effect of accidental asymmetries on the excitability of the LSP modes can be seen in the maps as the excitability is variable at the ends of different rods. Similar observations have been made in the complementary nanostructure of slot trimers in a gold film (Singh et al, 2018). The experimental maps differ from the simulated maps in Figures 1 and 2 in that the distinct resonances due to LSP modes cannot be clearly distinguished and mapped.…”

Algorithm‐Designed Plasmonic Nanotweezers: Quantitative Comparison by Theory, Cathodoluminescence, and Nanoparticle Trapping

“…[ 47 ] Coherent CL, so‐called because the emitted radiation has a constant phase relation with the electric field of the incoming electron, has mapped localized surface plasmon (LSP) resonances in coupled plasmonic systems produced by various methods, including chemical growth and electrostatic assembly, [ 48,49 ] electron beam lithography, [ 50,51 ] and ion beam milling. [ 52,53 ]…”

“…[47] Coherent CL, so-called because the emitted radiation has a constant phase relation with the electric field of the incoming electron, has mapped localized surface plasmon (LSP) resonances in coupled plasmonic systems produced by various methods, including chemical growth and electrostatic assembly, [48,49] electron beam lithography, [50,51] and ion beam milling. [52,53] Simulations are performed in COMSOL Multiphysics to gain insight into the CL measurements. We model the electron beam with a point dipole source placed just above the surface of the gold.…”

A review of defect engineering, ion implantation, and nanofabrication using the helium ion microscope

“…By optimizing the gold film itself to enable more uniform milling rates, for example, by increasing the grain sizes in polycrystalline films by annealing [ 179 – 180 ], or by using single-crystal gold [ 181 ], further improvements in both gap size and reproducibility can be achieved. Additional plasmonic structures that have been fabricated by helium FIB milling include trimeric assemblies of resonant nanoapertures [ 182 ], arrays of nanostructured radial resonant apertures [ 183 ], and plasmonic heptamer nanohole arrays [ 139 ] ( Figure 6h ), all in gold films, as well as multiresonant plasmonic nanoslit cavities [ 184 ] and plasmonic tetramer nanoantennae [ 51 ] in crystalline gold platelets. In the latter study, an advanced beam patterning toolbox with beam path optimization was recently introduced [ 51 ].…”