Description
Momentum-dependent electron energy-loss spectroscopy (q-EELS) has recently proven to be a pivotal tool for investigating charge excitations in suspended low-dimensional (2D) materials using a transmission electron microscope (TEM).
Unlike optical techniques, q-EELS provides access to the energy dispersion of phonons, excitons, and plasmons.
Comparing instead with other finite-momentum scattering techniques, such as neutron and X-ray spectroscopies, q-EELS with TEM does not require substrates or large crystals, making it an ideal tool to study freestanding 2D materials.
With sufficiently high momentum resolution, q-EELS can probe the optical-limit regime ($q \approx 0$) as well as low-momentum dispersions, thus enabling an unprecedented characterization of monolayer materials.
In this talk, I will discuss how the low-momentum loss functions of a 2D material can be linked to its optical properties introducing what we called optical conductivity approximation (OCA).
Then, I will present recent experimental observations of phonon, exciton, and plasmon dispersions in prototypical 2D materials and show how their peculiar 2D dispersions can be interpreted within the OCA framework.
