Unveiling breathing plasmon modes in aluminum metal–insulator–metal cavities by cathodoluminescence

Abstract

Aluminum (Al) processes excellent plasmon response from the ultraviolet (UV) to visible spectrum. Understanding of the deep sub-wavelength plasmon response of Al nanostructures is essential for the Al-based plasmon device design, such as UV surface-enhanced resonance Raman scattering and emission control of emitters. In this work, by using cathodoluminescence, the plasmonic properties of Al metal-insulator-metal (MIM) disk nanocavities are investigated. The resonant breathing modes rather than edge modes are resolved by the CL spectra and realspace mode patterns, which are in good agreement with the electromagnetic calculations. Moreover, the dispersion behavior of plasmon modes of the MIM cavity can be traced back to the propagating plasmon modes in an Al MIM slab, which shows that the electromagnetic fields are strongly confined in the cavities. Furthermore, a mode volume as small as 1.1×10 5 nm 3 is obtained for the 240 nm diameter cavity, demonstrating these MIM resonators to be ideal candidates for studies of strong plasmon-matter interactions.

Second harmonic generation from aluminum plasmonic nanocavities: from scanning to imaging

“…Despite their optical losses due to interband transitions (for Au at ∼520 nm), 28–34 Ag or Au surfaces are often used for plasmonic devices. Aluminum (Al), on the other hand, has no transition at the UV-visible and almost perfectly fits to the Drude free electron model, with a narrow interband transition in the near-infrared.…”

Nanoscopy of Aluminum Plasmonic Cavities by Cathodoluminescence and Second Harmonic Generation

“…[28][29][30] Plasmonic-based devices are often made of gold and therefore operate at wavelengths longer than 600 nm to avoid losses due to interband transitions that occur at about 550 nm. [31][32][33][34][35][36][37] Recently, aluminum has been recognized as the metal of choice for expanding photonic devices into the visible-UV range. [28,31,[38][39][40][41][42] Aluminum can be treated as an ideal Drude metal with no transition at the UV-visible, except a narrow interband transition at the near-infrared.…”

“…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.…”

Directional Chiral Optical Emission by Electron-Beam-Excited Nano-Antenna

“…By exciting an individual subwavelength nanoantenna with an electron beam, optical emissions can be effectively generated on subwavelength scales. [14,15] So far, polarization-resolved radiation, [16][17][18] angular emission, [19,20] and breathing plasmon modes [21,22] have been realized with nanoantennas. Among these previous studies, chiral emissions excited by electron beams from nanoantennas are particularly attractive.…”