Fig. 1. (a) Schematic illustration of the heterostructures. (b) Top-view SEM image of heterostructures, where Px equal to Py denotes the 450 nm period and W the 240 nm width of the nanoholes, H1 the top thickness of 80 nm, and H2 the vertical wall thickness of ∼10  nm. (c) The element components of Al and Si.

Fig. 2. For the spectral analysis, the reflection spectra under different incidence angles and azimuthal angles were collected by the angle-resolved spectrometer. (a) The diagram of the angle-resolved spectrometer, and θ and φ defined as illumination angle and azimuthal angle, respectively. (b) and (c) The variation of the optical properties with θ and φ, respectively, in case of illumination by an unpolarized white light. (d) The reflectance spectra of the Al nanostructures and the Al-Si heterostructures under varied illumination angle with φ set as 0°. (e) The FWHM of the pure Al nanostructures and the Al-Si heterostructures under the varied illumination angle with φ set as 0°. (f) The resonant linewidth comparison of the pure Al nanostructures and the Al-Si heterostructures under an incidence angle set as 75° with φ set as 0°.

Fig. 3. Mechanism of Al-Si heterostructures. (a) The resonant modes of the Al nanostructures and the Si nanostructures under varied incidence angles. (b) The energy levels of the Al nanostructures and Si nanostructures. The resonant modes of the Si nanostructures will couple to the (−1,0) SPP mode in case of spectral overlapping.

Fig. 4. Polarization-dependent optical properties of the heterostructures with an azimuthal angle of 0° by tuning the incident angles of (a) 30°, (b) 45°, and (c) 75° and with an illumination angle 60° by tuning the azimuthal angles of (d) 60°, (e) 75°, and (f) 90°.

Fig. 5. Imaginary part of the refractive index of the Si material is near zero in the visible and NIR regions.

Fig. 6. (a) The spectral analysis equipment of the angle-resolved spectrometer. (b) The diagram of θ and φ, defining the illumination angle and the azimuthal angle, respectively.

Fig. 7. Electromagnetic field distribution using commercial FDTD software. (a) The schematic illustration of heterostructures. (b) The electromagnetic field distribution in the x–y plane. (c) The electromagnetic field distribution in the y–z plane.

Fig. 8. Top-view SEM image of the Si nanoholes, where Px equal to Py denotes the 450 nm period and W the 240 nm width of the nanoholes.

Fig. 9. Reflectance spectra of the Si nanoholes arrays under varied θ. The resonant modes are at (a) 15°, (b) 30°, (c) 45°, and (d) 60°.

Fig. 10. Reflectance spectra of the Si nanoholes arrays under varied φ when θ is equal to 60°. The φ changes from 0° to 90°, and the step is 5°.

Fig. 11. Top-view SEM image of Al nanoholes, where Px equal to Py denotes the 450 nm period and W the 240 nm width of the nanoholes.

Fig. 12. Reflection spectra under different incident angles are collected by the angle-resolved spectrometer when the azimuthal angle equals 0°. The illuminating angle equals (a) 15°, (b) 30°, (c) 45°, and (d) 60°.