Cathodoluminescence Nanoscopy of 3D Plasmonic Networks

Abstract

Nanoporous metallic networks are endowed with the distinctive optical properties of strong field enhancement and spatial localization, raising the necessity to map the optical eigenmodes with high spatial resolution. In this work, we used cathodoluminescence (CL) to map the local electric fields of a three-dimensional (3D) silver network made of nanosized ligaments and holes over a broad spectral range. A multitude of neighboring hotspots at different frequencies and intensities are observed at subwavelength distances over the network. In contrast to well-defined plasmonic structures, the hotspots do not necessarily correlate with the network morphology, emphasizing the complexity and energy dissipation through the network. In addition, we show that the inherent connectivity of the networked structure plays a key optical role because a ligament with a single connected linker shows localized modes whereas an octopus-like ligament with multiple connections permits energy propagation through the network.

Cathodoluminescence Spectroscopy of Complex Dendritic Au Architectures for Application in Plasmon‐Mediated Photocatalysis and as SERS Substrates

“…[37] This complex morphology leads to broadband absorption in the visible and near infrared (Figure S1, Supporting Information), which results from the average of the multiple plasmon modes excited on the complex structures. [12] To characterize the spatial and energy distribution of the resonances, we use spatially resolved CL spectroscopy. We start by acquiring panchromatic CL maps: the CL signal is integrated over all the wavelengths that fall within the detector range.…”

Free-electron-light interactions in nanophotonics

“…The use of tightly focused electron beams allows for collecting spectral information directly from nanoscale samples with spatial resolution limited by the size of the focused electron beam. CL found applications in plasmonics, 7,[9][10][11][187][188][189][190][191][192][193][194] photonics, 195,196 semiconductors, [197][198][199] electron-beam lithography, 200 and tomographic reconstruction. 201 Additionally, the combination of spatial and spectral resolution can be combined to measure the dispersion of CL effects such as SPR.…”

Nanoscopy of Aluminum Plasmonic Cavities by Cathodoluminescence and Second Harmonic Generation

“…[5][6][7][8][9] On such complex structures, neighbouring metallic nanostructures, nanoparticles, or cavities can interact to form local hot spots with desired frequencies, polarizations, and other light properties. [6][7][8][9][10][11][12] During recent years, plasmonic structures with specific optical properties have been fabricated, showing enhanced nonlinear properties, [6,[13][14][15][16][17][18] refractive index modulation, [19] deep subwavelength electromagnetic (EM) field confinement, [20][21][22] cloaking, [23,24] negative refraction, [25] and even more exotic properties. [21,26] These optical properties are governed by the complex dielectric function of the metal, the geometrical parameters of the subwavelength structures, [27] and by their arrangement onto the surface.…”

“…to map the local electric fields with a nanoscale resolution. [10,11,37,38,41,42,50,[60][61][62][63][64][65][66] We shall point out that far-field optical measurements are less adapted for characterizing these structures as local effects and spectral resonances are averaged resulting in a broad spectral response.…”

“…By using raster scanning, it is possible to retrieve the full spectrum from each pixel of the entire scan, and thus to map the local electric fields with a nanoscale resolution. [ 10,11,37,38,41,42,50,60–66 ] We shall point out that far‐field optical measurements are less adapted for characterizing these structures as local effects and spectral resonances are averaged resulting in a broad spectral response.…”