Characterizing Quantum Emitters at the Nanoscale with Time-Resolved Cathodoluminescence in a Scanning Transmission Electron Microscope.

Combining a scanning transmission electron microscope with cathodoluminescence (STEM-CL) allows researchers to simultaneously acquire atomic scale structural and compositional information along with local optical properties of the sample. Such CL systems have been applied for examining quantum dots, color centers in wide bandgap materials, and other quantum emitters (QE), allowing the establishment of direct correlation between the material’s structural feature and its optical properties. Our research demonstrates an integration of high temporal-resolution into the STEM-CL system, allowing the research of the fast processes during the QEs’ photon emissions. The temporal resolution is achieved with a simple pump-probe mechanism, where fast (ns) and ultrafast (ps) electron pulses are utilized as pump, while the photons generated by the CL processes are sent into a time-correlated-single-photon-counting device to reveal the temporal information. The system is set up on an aberration corrected STEM equipped with the CL module. An initial demonstration experiment was carried out with as short as 5 ns electron pulses generated by the beam blanker to obtain the spatially resolved radiative decay lifetime of Ce-doped YAG nanoparticles. Anticipated upgrades to the system will include an RF module to pitch the electron beam in GHz frequency, creating ps electron pulses, pushing the temporal-resolution to ps region. An HBT interferometer is also integrated to the CL module allowing simultaneous anti-bunching measurements. The details of the system and the preliminary results will be shown in the presentation.