Plasmon Launching and Scattering by Silicon Nanoparticles

Abstract

Resonant optical nanomaterials with a high refractive index, such as silicon, have become key elements for controlling free-space light. Here, we show that silicon nanoparticles can manipulate highly confined guided waves in the form of surface plasmon polaritons (SPPs) on a subwavelength scale. Using electron energy-loss spectroscopy in a transmission electron microscope, we demonstrate that SPPs in ultrathin metal films can be efficiently launched due to the strong coupling between the Mie resonances of the nanoparticle and the SPP modes. We find that the SPP excitation wavelength can be tuned across the entire nearinfrared by varying the particle size. For insight into the coupling mechanism, we also measure the electron-beam-induced response of the Mie resonances in isolated silicon nanostructures in a broad size range. Finally, we show that the silicon nanoparticles act as scatterers of the SPPs supported by the film. Our results may pave the way for using high-refractive-index dielectric nanoantennas as compact elements for manipulating highly confined SPPs.

Computational Discovery and Experimental Demonstration of Boron Phosphide Ultraviolet Nanoresonators

“…The position of the beam is directly related to the excitation efficiency of the optical modes, [ 59 ] and thus, by judicious positioning of the beam we can selectively excite different Mie modes. [ 55 ] When the beam is positioned in the center of nanoparticle, we observe a distinct resonance in the ultraviolet at 3.99 eV. As the beam is moved closer to the surface of the nanoparticle, two additional resonances are observed at the energies 3.57 and 2.77 eV.…”

“…The experimental EELS intensity maps (Figure 4h–j) of these three Mie modes are in good agreement with the simulations as well as previous EELS measurements performed on Mie‐resonant Si nanoparticles. [ 55,56 ]…”

“…The energy loss was then calculated as the work rate done on the electron beam by the induced electromagnetic field. [55] Dark-Field Scattering Measurements: A custom-built inverted optical microscope was used for dark-field scattering spectroscopy of single nanoparticles (Figure 3a). For the measurements presented in Figure 3, the sample is illuminated from the top by a halogen lamp through a dark field condenser and the scattered light was collected by an objective (50×, NA = 0.8).…”

“…The experimental EELS intensity maps (Figure 4h-j) of these three Mie modes are in good agreement with the simulations as well as previous EELS measurements performed on Mie-resonant Si nanoparticles. [55,56] The dark-field scattering measurements (Figure 3) combined with the EELS measurements (Figure 4) show that the optically resonant nature of the BP nanoparticles can be identified both in their far-field and near-field responses, respectively. These resonances are present both in the visible and ultraviolet and their resonance energies can be tuned with particle size.…”

“…To gain more insight into the nature of these resonances and to access the ultraviolet spectral region, we also perform near-field characterization on similar BP nanoparticles using electron energy-loss spectroscopy (EELS). EELS is performed in a transmission electron microscope and has been employed to access near-field properties of both metallic [53,54] and dielectric nanostructures [55][56][57] as well as optical devices. [58] The combined high spatial and spectral resolution of EELS provides unique nanoscale information on optical modes over a broad spectral range.…”