Inelastic electron scattering at large angles: the phonon polariton contribution

TL;DR

This paper investigates how inelastic electron scattering at large angles involves phonon polaritons in materials like SrTiO3, PbTiO3, and SiC, revealing that polaritons can be excited via multiple scattering, contrary to previous assumptions.

Contribution

It introduces a comprehensive framework combining dielectric theory, DFT, and simulations to understand phonon polariton contributions in high-angle electron scattering.

Findings

Phonon polaritons can be excited at large scattering angles.

Multiple scattering enables polariton excitation in electron energy-loss spectroscopy.

The relative contribution depends on structure factor and scattering angle.

Abstract

We explore the inelastic electron scattering in SrTiO3, PbTiO3, and SiC in their phonon energy range, challenging the assumption that phonon polaritons are excluded at large angles in high-resolution transmission electron energy-loss spectroscopy. We demonstrate that through multiple scattering, the electron beam can excite both phonons and phonon polaritons, and the relative proportion of each varies depending on the structure factor and scattering angle. Integrating dielectric theory, density functional theory, and multi-slice simulations, we provide a comprehensive framework for understanding these interactions in materials with polar optical phonons.