Unveiling quasi-dark surface plasmon modes in Au nanoring cavities by cathodoluminescence

Abstract

Spectral resolving and imaging surface plasmon modes in noble metal nanostructures are important for applications in nanophotonics. Here, we use cathodoluminescence (CL) spectroscopy to excite and probe quasi-dark plasmon modes of Au nanoring cavities. Numerical simulations of both the spectra and the electromagnetic field distribution are carried out by using boundary element method. Good agreement between the experimental and simulated results is obtained. Particularly, CL is shown as an efficient method to probe quadrupole modes, which is difficult for traditional optical means. Moreover, a high Purcell factor in excess of 100 is obtained for the dark quadrupole modes in gold ring cavities. Our work provides an efficient way to explore the initial nature of surface plasmon modes in metal nanostructures.

Plasmonic Hot Carriers Imaging: Promise and Outlook

“…Therefore, both aforementioned imaging techniques are accessible to dipolar modes that are manifested due to radiative losses, whereas higher-order modes are only captured by EELS, underscoring their ability to detect nonradiative modes (Figure d). It is also in qualitative agreement with observations of dark-mode plasmons which are mostly probed by EELS, not by CL . Additionally, in contrast with SEM, PEEM has been suggested as a powerful technique to capture a LSPR near-field intensity map.…”

“…It is also in qualitative agreement with observations of dark-mode plasmons which are mostly probed by EELS, not by CL. 76 Additionally, in contrast with SEM, PEEM has been suggested as a powerful technique to capture a LSPR near-field intensity map. By employing multiphoton PEEM system with ultrashort-pulsed laser, it enabled timeresolved photoemitted electron measurement, which visualized the dynamics of LSPRs for different Au nanostructures within spatial resolution of sub-10 nm.…”

Tunable Multipolar Surface Plasmons in 2D Ti3C2Tx MXene Flakes

“…Light–matter interactions at the nanoscale have been greatly enriched by the collective oscillations of free charge carriers, commonly known as surface plasmons (SPs). − The ability to manipulate light at nanometer scales through coupling with resonating SPs is known to enhance the performance of numerous applications ranging from biological, chemical, and optical sensors to photovoltaic devices and surface-enhanced Raman spectroscopy (SERS). − ,− Despite the predominance of metallic nanostructures, e . g ., gold, silver, aluminum, and copper, in plasmonic applications, ,, SP excitations are not necessarily limited to metals and are already evidenced in other materials with substantial free charge carrier density. , In this regard, owing to their reduced dimensionality, 2D materials stand out for their electronic and photonic properties. − The outstanding light confinement at their surfaces makes them excellent candidates for the plasmonic platform. − Thus far, several 2D materials such as graphene, ,, black phosphorus, hexagonal boron nitride, transition metal chalcogenides, e .…”

“…In this context, electron energy loss spectroscopy (EELS) in conjunction with scanning transmission electron microscopy (STEM) stands out for its technical capability to investigate local SP modes with high spatial resolution, ,,, where the incident fast electrons couple to the SPs, resulting in inelastic kinetic energy losses. ,,, In contrast to light-based techniques with very reduced spatial resolution due to light diffraction limit, , electron beams allow the excitation of both optically active and forbidden SP modes. ,,,, Those modes have been extensively analyzed in metal nanostructures, e . g ., gold and silver, by the use of STEM-EELS. ,,, However, to our knowledge, no progress has been made on specific plasmon modes sustained by Ti 3 C 2 T x , neither their thickness-dependence nor morphological-dependence, i .…”

Evolution and Coupling of Plasmonic Modes in Single-Crystal Aluminum Nanoridge Antennas

“…The spatial distributions of the emission intensity corresponds to the SPP standing wave patterns and these resonance orders with mode number m = 2–5 can be distinguished clearly. It is worth noting here that the even-order resonances can be probed by CL technique, ,, however, it is not possible with optical excitation under normal incidence. Moreover, in this Fabry–Perot resonance case, the plasmon wavelength can be deduced from the antinode spacing, which equals to λ SPP /2.…”