Speaker
Description
We present pump-probe cathodoluminescence (CL) spectroscopy using two new ultra-fast SEM instruments that we have developed in our group: one based on an electrostatic beam blanker (electron pulse duration 15 ps at 5 keV) synchronized with a 1-ns 442 nm pulsed laser, and one based on photoemission using a 500-fs 1034 nm pulsed pump laser, upconverted to 257 and 345 nm, creating 1-10 ps electron pulses with 1-300 electrons/pulse.
Using electrostatic beam blanking we study pulsed laser excitation of silicon nanospheres with strong CL Mie resonances in the visible spectral range. Ultrafast laser local heating leads to thermo-optic spectral shifts of the Mie modes. Synchronizing nanosecond pulsed laser excitation with nanosecond electron pulses allows us to probe the temporal evolution of these shifts and monitor nanoscale heating dynamics. These results demonstrate how dielectric Mie resonances, probed with USEM-CL, can serve as sensitive probes for nanoscale thermometry with potential applications in photocatalysis in semiconductor integrated circuit metrology.
Using ultrafast photo-emission microscopy we study charge carrier dynamics in Cu2ZnSnS4 (CZTS), an earth-abundant semiconductor material for photovoltaic applications whose performance is strongly limited by defect-mediated recombination. Delay-dependent pump-probe USEM-CL measurements reveal transient enhancement and suppression of the CL probe intensity following optical pumping, which can be described using a defect-assisted two-trap recombination model involving competing non-radiative and radiative pathways of which we determine the decay rates. These results establish pump-probe USEM-CL as a powerful method for probing recombination dynamics in complex semiconductors, potentially also at high spatial resolution.