Speaker
Description
Cathodoluminescence (CL) is a technique for investigating various electron–matter interactions by measuring electron-beam-induced photon emission. It provides access to nanoscale luminescence processes such as defect emission¹, carrier recombination², carrier diffusion³, and plasmon-related emission⁴. Time-resolved (TR) CL combined with ultrafast transmission electron microscopy (UTEM) offers a platform that integrates the local excitation capability of electron microscopy with TR photon detection, enabling the analysis of electron-beam-induced luminescence dynamics from both spatial and temporal perspectives.
The luminescence signal observed in UTEM-based TR-CL is not determined solely by the intrinsic optical properties of the material. The acceleration voltage can alter the penetration depth, energy-loss distribution, excitation volume, sample damage, and surface/bulk contributions of the electron beam, thereby affecting the observed CL intensity, spectral characteristics, and TR luminescence response. This consideration becomes particularly important for TR-CL measurement with ps resolution using streak camera, where relatively low detection sensitivity and electron-pulse broadening under low-acceleration-voltage conditions can degrade the effective temporal resolution. Therefore, UTEM-based TR-CL requires the selection of acceleration voltage and beam conditions that are not only suitable for obtaining sufficient CL signal but also for resolving the luminescence dynamics of interest.
Here, we introduce a UTEM-based TR-CL platform, along with initial measurement results obtained using this system. The platform consists of a CL collection optical path coupled to UTEM, together with TR detection modules based on time-correlated single-photon counting (TCSPC) and a streak camera. TCSPC-based detection is advantageous for high-sensitivity CL decay measurements over long time ranges, whereas streak-camera-based detection, although relatively less sensitive, is suitable for tracking fast luminescence dynamics in the picosecond time regime⁵. Based on measurements from representative luminescent samples, we compare how experimental conditions such as acceleration voltage, beam current, and light-collection efficiency affect the CL signal and the effective temporal resolution, and discuss the condition-setting process required for TR-CL measurement with ps resolution using streak camera. Through this work, we aim to demonstrate the potential of this platform for future studies of nanoscale luminescence dynamics, including defect emission, charge recombination, and beam-induced optical responses.
References
1. Bourrellier, R. et al. Bright UV single photon emission at point defects in h-BN. Nano Lett. 16, 4317–4321 (2016).
2. Zagonel, L. F. et al. Nanometer scale spectral imaging of quantum emitters in nanowires and its correlation to their atomically resolved structure. Nano Lett. 11, 568–573 (2011).
3. Kim, Y.-J. & Kwon, O.-H. Cathodoluminescence in ultrafast electron microscopy. ACS Nano 15, 19480–19489 (2021).
4. Chaturvedi, P. et al. Imaging of plasmonic modes of silver nanoparticles using high-resolution cathodoluminescence spectroscopy. ACS Nano 3, 2965–2974 (2009).
5. Shima, K. et al. Spatio-time-resolved cathodoluminescence study on the midgap recombination lifetimes of nanowire-based InGaN/GaN multiple quantum shells. Appl. Phys. Lett. 128, 122105 (2026).