Fig. 1. Optical resonances supported by a Si/Si3N4/Ag nanocavity. (a) Schematic configuration of a Si/Si3N4/Ag hybrid nanocavity. (b) Calculated scattering spectra (normalized to the maximum value) of Si/Si3N4/Ag nanocavities (d=195  nm, h1=50  nm) with variable Si3N4 spacer layer thickness. (c)–(e) Comparison of the scattering spectra (each spectrum is normalized to its maximum value) of Si nanoparticles with different diameters placed on a Si3N4/Ag/SiO2 substrate (h1=50  nm, h2=95  nm) (red curves) and a SiO2 substrate (blue curves).

Fig. 2. Physical mechanism for the enhanced nonlinear optical emission from a Si/Si3N4/Ag nanocavity. (a) Energy band diagram of Si and carrier dynamics in a Si nanoparticle excited by femtosecond laser pulses. (b) Calculated scattering and 2PA/3PA spectra for a Si nanoparticle (d=195  nm) placed on a Si3N4/Ag/SiO2 substrate. The scattering spectrum is normalized to its maximum value. (c), (d) Electric field amplitude distributions in the Si/Si3N4/Ag hybrid nanocavity calculated at the ED and MD resonances.

Fig. 3. Nonlinear optical emission from a Si/Si3N4/Ag nanocavity under the excitation of femtosecond laser pulses. (a) PL spectra of the Si/Si3N4/Ag nanocavity measured at different pumping pulse energies. The corresponding CCD images of the emission from the Si/Si3N4/Ag nanocavity are shown in the insets. (b) Backward scattering spectra (normalized to the maximum value) measured for the Si/Si3N4/Ag nanocavity before and after the luminescence burst. The scanning electron microscope (SEM) image of the Si nanoparticle before the excitation is shown in the inset. (c) Dependence of the integrated PL intensity on the pumping pulse energy observed for the Si/Si3N4/Ag nanocavity. (d) PL spectra of a Si nanoparticle placed on a SiO2 substrate measured at different pumping pulse energies. (e) Forward scattering spectra (normalized to the maximum value) measured for the Si nanoparticle placed on the SiO2 substrate before and after the luminescence burst. (f) Dependence of the integrated PL intensity on the pumping pulse energy observed for the Si nanoparticle placed on the SiO2 substrate.

Fig. 4. Coupling between the TE wave supported by a Si3N4/Ag heterostructure and the Mie resonances supported by a Si nanoparticle in a Si/Si3N4/Ag nanocavity. (a) Schematic showing the excitation of a Si/Si3N4/Ag nanocavity by using the TE wave propagating on the surface of the Si3N4/Ag heterostructure stimulated by s-polarized incident light. The electric component (E) of TE wave is concentrated on the surface of the Si3N4 spacer, while the corresponding magnetic component (H) mainly exists at the Si3N4/Ag interface. (b) Backward scattering spectrum of the Si/Si3N4/Ag nanocavity. The SEM image of the Si nanoparticle is shown in the inset. (c) Measured scattering spectra of the Si/Si3N4/Ag nanocavity excited by s-polarized light with different incident angles. The corresponding CCD images of the scattering are shown in the insets. The wavelength bands where MQ, ED, and MD exist are denoted by green, yellow, and red shadows, respectively. The angular dispersion of the TE wave is represented by a dashed curve, schematically. (d) Simulated scattering spectra (in a relative scale) of the Si/Si3N4/Ag nanocavity excited by s-polarized light with different incident angles.

Fig. 5. Exciton-photon coupling in a Si/Si3N4/Ag nanocavity with an embedded WS2 monolayer. (a) Schematic showing the excitation of a Si/Si3N4/Ag nanocavity with an embedded WS2 monolayer and the detection of the scattered light. The SEM and forward scattering images of Si/Si3N4/Ag nanocavities with an embedded WS2 monolayer are shown in the insets. (b), (c) Angle-resolved scattering spectra of the Si/Si3N4/Ag nanocavity (d∼190  nm) with an embedded WS2 monolayer. Each of the spectra is normalized to its maximum value. The CCD images of the scattered light are shown in the insets. (d), (e) Dispersion relations of the upper and lower polariton branches (purple dots) extracted from the angle-resolved scattering spectra of the Si/Si3N4/Ag nanocavity with an embedded WS2 monolayer around the resonant wavelengths of the XA and XB. The red and blue curves are the fittings of the dispersion relations based on the coupled harmonic oscillator model. The energies of the excitons and photons (TE wave) are indicated by dashed lines.

Fig. 6. Multipolar decomposition for resonances of the Si/Si3N4/Ag nanocavity (d=195  nm, h1=50  nmh2=95  nm). The dashed curve represents the sum of the scattering cross section of the four multipolar components. (a) The nanocavity is excited by a plane wave with normal incidence. (b) The nanocavity is excited by the simultaneous incidence of s-polarized and p-polarized plane waves with an incident angle of 53°.

Fig. 7. Simulated scattering spectra (in a relative scale) of Si/Si3N4/Ag nanocavities (d=195  nm, h2=95  nm) with different thicknesses of the Ag layer. The excitation light is a plane wave with normal incidence.

Fig. 8. Simulated results of the Si nanoparticle (d=195  nm) placed on a SiO2 substrate. (a) Scattering and 2PA/3PA spectra. The scattering spectrum is normalized to its maximum value. (b), (c) Electric field amplitude distributions at the ED and MD resonances.

Fig. 9. (a) PL spectrum of the WS2 sample placed on the Si3N4/Ag heterostructure using a 488 nm excitation laser with a power of 0.5 mW. (b) Raman spectrum of using a 633 nm excitation laser.

Fig. 10. Schematic diagram of experimental setups for measuring the nonlinear optical emission from the Si/Si3N4/Ag nanocavity under the excitation of femtosecond laser pulses.

Fig. 11. Simulated scattering spectra (in a relative scale) of a PS nanoparticle (d=300  nm) placed on the Si3N4/Ag heterostructure excited by s-polarized light in the Kretschmann-Raether configuration with different incident angles.

Fig. 12. Simulated angle resolved scattering spectra of the Si/Si3N4/Ag nanocavity with an embedded WS2 monolayer under the excitation of s-polarized plane wave.