The content provides an overview of the developments and advancements in atomic-resolution vibrational EELS. Key highlights include:
Experimental setup and capabilities: The introduction of the ground-potential monochromator enabled combining high-resolution imaging/diffraction with meV energy resolution needed to detect vibrational modes. This allows for atomic-scale spatial resolution and sensitivity to localized vibrations.
Scattering mechanisms: Dipole scattering leads to delocalized signals, while impact scattering is localized to atomic sites. Dark-field EELS can suppress the delocalized dipole scattering to enhance the localized phonon signal.
Demonstrations of atomic-resolution: Several studies have shown atomic-level variations in the phonon signal, mapping modulations with the crystalline lattice and identifying localized vibrations around defects and grain boundaries.
Theoretical models: Two key theoretical frameworks, the frequency-resolved frozen phonon multislice and the Bloch wave-based approach, are discussed to accurately account for phonon scattering in simulations, including dynamic diffraction effects.
Future perspectives: Optimization of dark-field signal collection, adding momentum-resolution, and combining with tip-enhanced Raman spectroscopy are proposed as promising future directions to further advance atomic-resolution vibrational EELS.
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