Kavli Affiliate: Scott K. Cushing
| First 5 Authors: Wonseok Lee, Wonseok Lee, , ,
| Summary:
Time-resolved and ultrafast electron energy-loss spectroscopy (EELS) is an
emerging technique for measuring photoexcited carriers, lattice dynamics, and
near-fields across femtosecond to microsecond timescales. When performed in
either a specialized scanning transmission electron microscope or ultrafast
electron microscope (UEM), time-resolved and ultrafast EELS can directly image
charge carriers, lattice vibrations, and heat dissipation following
photoexcitation or applied bias. Yet recent advances in theoretical
calculations and electron optics are often required to realize the full
potential of ultrafast EEL spectrum imaging. In this review, we present a
comprehensive overview of the recent progress in the theory and instrumentation
of time-resolved and ultrafast EELS. We begin with an introduction to the
technique, followed by a physical description of the loss function. We outline
approaches for calculating and interpreting ground-state and transient EEL
spectra spanning low-loss plasmons to core-level excitations analogous to X-ray
absorption. We then survey the current state of time-resolved and ultrafast
EELS techniques beyond photon-induced near-field electron microscopy,
highlighting abilities to image carrier and thermal dynamics. Finally, we
examine future directions enabled by emerging technologies, including electron
beam monochromation, in situ and operando cells, laser-free UEM, and high-speed
direct electron detectors. These advances position time-resolved and ultrafast
EELS as a critical tool for uncovering nanoscale dynamic processes in quantum
materials and solar energy conversion devices.
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