Exploring electronic, optical and vibrational properties of low-dimensional materials using monochromated EELS

Low-dimensional materials, such as fullerenes, carbon nanotubes, graphene, hexagonal boron nitride and transition metal dichalcogenides have garnered significant attention as candidates for next-generation device components. Their distinctive properties stem from reduced dimensionality and are significantly influenced by the behavior of quasiparticles, including excitons and phonons, particularly in non-periodic structures like vacancies and edges. Correlating local atomic structures with spectral features is crucial for elucidating their physical properties. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (EELS) offers localized spectral information at the single-atom level, providing valuable insights for materials characterization. Recent advances in monochromators for transmission electron microscopy have enhanced the energy resolution of EELS, enabling the measurement of optical and vibrational absorption properties at the nanoscale and atomic level. Additionally, phenomena like optically forbidden excitations and modulation of the local phonon density of states, previously inaccessible via conventional spectroscopic methods, are now observable. This review summarizes recent advancements in using monochromated transmission electron microscopy to characterize low-dimensional materials.