Cathodoluminescence spectroscopy has emerged as a powerful tool for probing plasmonic phenomena in metallic nanostructures, particularly in the study of localized surface plasmon resonances and hot carrier dynamics. The technique leverages the interaction of a focused electron beam with nanostructured metals to generate and map plasmonic responses with nanoscale spatial resolution, providing insights into light-matter interactions at subwavelength scales.
Localized surface plasmon resonances (LSPRs) occur when conduction electrons in metallic nanostructures collectively oscillate under external excitation, leading to enhanced near-field effects and characteristic far-field scattering. Cathodoluminescence enables direct visualization of these resonances by detecting the emitted photons resulting from electron-induced plasmon decay. Unlike optical excitation methods, electron beams offer superior spatial resolution, often below 10 nm, allowing for precise mapping of plasmon modes in complex nanostructures such as nanodimers, oligomers, and patterned metasurfaces.
One key application is the spectral and spatial mapping of LSPRs in individual nanostructures. For example, gold and silver nanoparticles exhibit distinct cathodoluminescence peaks corresponding to their dipolar, quadrupolar, and higher-order plasmon modes. By scanning the electron beam across a nanostructure, researchers reconstruct the spatial distribution of these modes, revealing how geometric parameters like shape, size, and interparticle spacing influence plasmon coupling. This capability is critical for designing plasmonic devices with tailored optical responses, such as ultra-sensitive sensors or nanoantennas for light harvesting.
Another significant application is the investigation of hot carrier generation in plasmonic systems. When plasmons decay non-radiatively, they can generate highly energetic electron-hole pairs, known as hot carriers, which have potential applications in photocatalysis, photodetection, and energy conversion. Cathodoluminescence provides a means to study these processes by analyzing the emission spectra and lifetime of plasmon-generated photons. The electron beam’s precise excitation location allows researchers to correlate hot carrier production with specific plasmon modes, offering insights into the efficiency and spatial distribution of carrier generation.
In metallic nanostructures with sharp tips or gaps, cathodoluminescence reveals enhanced electric fields due to plasmonic hot spots. These regions exhibit intense emission peaks, indicating strong light confinement, which is useful for surface-enhanced spectroscopy and nonlinear optical applications. Additionally, the technique helps quantify losses in plasmonic systems, distinguishing between radiative damping and absorption losses, which is essential for optimizing plasmonic device performance.
Recent studies have employed cathodoluminescence to explore hybrid plasmonic systems, where metallic nanostructures are coupled to dielectric or semiconductor components. By mapping plasmon resonance shifts and mode hybridization, researchers gain a deeper understanding of energy transfer mechanisms and the role of near-field coupling in these systems.
The ability to probe plasmonic phenomena at the nanoscale without diffraction-limited constraints makes cathodoluminescence indispensable for advancing plasmonics research. Its applications extend to designing efficient plasmonic circuits, optimizing hot carrier extraction, and developing next-generation nanophotonic devices. As electron microscopy techniques continue to improve, cathodoluminescence will remain a vital tool for unraveling the intricate interplay between plasmons and light at the nanoscale.
The quantitative analysis of cathodoluminescence data often involves correlating emission spectra with numerical simulations, such as finite-difference time-domain (FDTD) calculations, to validate observed plasmon modes. For instance, studies on silver nanorods have shown cathodoluminescence peaks at wavelengths matching simulated LSPR positions, confirming the technique’s accuracy in mode identification. Similarly, the emission intensity profiles of gold bowtie antennas align with theoretical predictions of field enhancement, demonstrating the reliability of cathodoluminescence for plasmonic characterization.
In summary, cathodoluminescence serves as a critical experimental method for investigating plasmonic effects in metallic nanostructures, offering unmatched spatial resolution and detailed spectral information. Its applications in LSPR mapping and hot carrier studies provide foundational knowledge for advancing nanophotonics, enabling the development of innovative plasmonic technologies with enhanced optical performance.