"Incoherent and coherent cathodoluminescence spectroscopy –nanoscale light distribution in semiconductors"

Abstract:

The growing demand for precise nanoscale characterization tools has driven advancements in techniques capable of probing optical and thermal phenomena beyond the diffraction limit. In this work, we highlight recent developments in cathodoluminescence (CL) spectroscopy within a scanning electron microscope (SEM), enabling high-resolution studies of light-matter interactions at the nanometer scale.

In the first part, we demonstrate a novel approach to nanoscale thermometry using coherent CL from individual crystalline silicon nanospheres (NPs, d ~ 200–240 nm) exhibiting optical Mie resonances. By coupling 442-nm laser light into the SEM, we locally heat individual nanoparticles and use the electron beam as a probe to monitor spectral shifts in the Mie modes. The electric quadrupole (EQ) mode serves as a sensitive temperature indicator, exhibiting red-shifts up to 100 meV corresponding to temperatures as high as 575°C. Thermal simulations reveal that the heat dissipation is highly dependent on the NP’s contact area with the 15 nm-thin SiN membrane. We further implement a pump-probe CL technique by synchronizing ns-laser and electron pulses, allowing us to investigate the temporal dynamics of heating and cooling processes in a single NP. This approach opens new pathways for localized, time-resolved thermometry with potential applications in integrated electronics, optoelectronics, and nanoscale heat management.

In the second part, we explore the structural-optical correlations in polycrystalline CsPbBr₃ perovskite films. By combining electron backscatter diffraction (EBSD) and CL spectroscopy on the same region, we achieve the first direct mapping of crystal orientation with optical emission at the nanoscale. While grain orientation does not significantly affect intra-grain CL emission, a strong decrease in CL intensity is observed at grain boundaries. Depth-resolved CL and optical simulations reveal the key roles of carrier diffusion and outcoupling in shaping the spectral response.

Together, these results illustrate the strength of SEM-based CL spectroscopy for in-situ exploration of structural, optical, and thermal properties in functional nanomaterials, with broad relevance to materials science, photonics, and device engineering.