Recently, electron-beam spectroscopy techniques have emerged as powerful probes in nanoscience due to their ability to generate, probe, and control light at length scales far below the diffraction limit of light. Taking advantage of the extremely high spatial resolution, novel techniques have appeared that combine electron beam excitation with optical spectroscopy. Spatially-resolved cathodoluminescence (CL) spectroscopy, in which the electron-beam-induced radiation is collected inside an electron microscope, is one of these techniques that holds great potential for nanoscience. For a long time CL spectroscopy was mainly used in geology to analyze minerals, but in the past two decades its scope has expanded significantly. Recently it has been used to study fundamental optical properties of a myriad of metallic, semiconductor, and dielectric (nano)materials in the fields of materials science and nanophotonics, including plasmonics and metamaterials. We have developed a special version of CL spectroscopy in which we can both effectively measure the emitted spectrum as well as the angular emission distribution (SPARC) .
The SPARC system is integrated with a standard commercially available scanning electron microscope (SEM). SEMs are relatively easy to operate and do not require electron-transparent samples as is the case for TEM work. Additionally, the vacuum chamber is more spacious providing more flexibility. As a result SEM-CL is widely applicable and easy to use.
Here we present how the technique can be employed to study the fundamental optical properties of metallic and semiconductor nanostructures including the spectral response, directionality, polarization response, and the 3D near-field distribution. This opens up new avenues for peforming multipolar decomposition of the scattering, probing dispersion, coherent control of light on the nanoscale, probing chirality, beaming of light, and studying the 3D optical response of complex nanophotonic structures. Systems that can be studied include nanoantennas, photonic crystals, MIM plasmon resonators, nanowires, bull's eyes etc.