Direct imaging of hybridized eigenmodes in coupled silicon nanoparticles

Abstract

High-index dielectric nanoparticles support leaky geometrical resonances in the visible spectral range with large interaction cross sections, and find applications in nanoscale optoelectronic devices and surface coatings. Coupling between such resonant nanoparticles in close proximity can give rise to enhanced directionality and confinement. Here, we combine dark-field (DF) scattering spectroscopy with cathodoluminescence (CL) imaging spectroscopy to study hybridization of resonant modes in coupled silicon nanoparticles and directly image the modal field profiles of these hybridized eigenmodes. The DF measurements show a strong influence of the gap size on the scattering spectrum as a result of hybridization. Using finite-element modeling we calculate the eigenmodes of the dimer and identify the hybridized eigenmodes in the scattering spectrum. CL imaging spectroscopy is used to directly map the modal field profiles of single particles and dimer structures with deep-subwavelength spatial resolution. Detailed comparison with eigenmode calculations shows that the measured modal field profiles correspond to the hybridized symmetric electric and antisymmetric magnetic bonding modes. We study dimers composed of large dielectric bars to explore the ability of CL imaging to map highly complex hybridized field profiles inside resonant nanostructures. Our results demonstrate the ability to characterize the complex resonant properties of coupled nanostructures, paving the way for more complex applications and devices based on resonant dielectric nanoparticles.

Unidirectional light scattering with high efficiency at optical frequencies based on low-loss dielectric nanoantennas

“…The equations (11) and (12) were satisfied around 650 nm at which unidirectional forward scattering was observed in the FDTD numerical simulation. This agreement strongly suggest that the first Kerker condition was achieved with the asymmetric dimer configuration around 650 nm, at which the resonant scattering peak was also observed.…”

“…This drawback has hampered the realization of the aforementioned applications using metallic plasmonic nanoparticles 7 and stimulated the study of high-refractive-index dielectric nanoparticles as an alternative. For instance, dimers or oligomers of silicon nanostructures have been revealed to enhance and confine the electromagnetic field into the gap region, and increase the scattering efficiency, without appreciable heat generation [8][9][10][11][12][13][14][15][16] . These dielectric nanoantennas can be exploited, for example, by spectroscopic techniques such as fluorescence microscopy or surface enhance Raman scattering, where undesired heat could disturb the response of the sample 17 .…”

Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies

“…The mode coupling effect we report on is different from hybridization [46] which is observed with plasmonic metameterial [12,47], split-ring resonators metametarials [48], inductor-capacitor resonators [49], cut wires [50], nanowires [51], nano-rings [52], nanoparticle dimers [53] or silicon nanoparticles [54]. In the latter cases, the coupling between the two identical meta-atoms which constitute the dimer leads from a trapped mode to the formation of new hybridized modes because it lifts the degeneracy of the mode of the individual meta-atoms.…”

Electromagnetic polarization-controlled perfect switching effect with high-refractive-index dimers and the beam-splitter configuration

“…However, the challenge of building good sphere dimmers with controlled separation still remains although there are some recent good examples in the literature, like those in refs 23, 40. Other geometries like either cubes41 or cylinders1142 could constitute suitable alternatives for building this kind of dimer units. Also, with reference to the experiment in the optical range, the widely used backward dark field microscope configuration (BDFMC) (see for instance, refs 17, 43 among others) could be used to reproduce the results contained in this research, although our findings are mainly addressed to a final in-plane optical-board set-up.…”