Recent Progress of Vibrational Electron Energy-Loss Spectroscopy in Scanning Transmission Electron Microscope

With the recent developments of dedicated aberration correctors and monochromators, scanning transmission electron microscopes(STEMs) are playing an increasingly important role in condensed matter physics and materials science.Here, we review the progress of vibrational electron energy-loss spectroscopy(EELS) in STEM in the past decade.The technique termed four-dimensional EELS(4 D-EELS) has made it possible to probe lattice dynamics with both nanometer spatial resolution and fine momentum resolution.High spatial resolution in STEMs also enables atomically-resolved vibrational measurements to extract the local projected density of states(PDOS).Besides, electron scattering offers a large momentum transfer and a wide detection spectral range, providing new opportunities to investigate phonon polaritons complementary to conventional optical methods.Finally, prospects for future developments of vibrational STEM-EELS studies are also discussed.