Simulations of angle- and spatially-resolved vibrational electron energy loss spectroscopy for a system with a planar defect

TL;DR

This paper advances the theoretical simulation of vibrational electron energy loss spectroscopy (EELS) by modeling angle- and spatially-resolved spectra at atomic scales, revealing defect-induced phonon density of states variations.

Contribution

It introduces a detailed simulation method for vibrational EELS with nanometer and atomic resolution, focusing on systems with planar defects, enhancing interpretation of experimental data.

Findings

Spectral shape varies with defect presence and probe size.

Atomic scale contrast enhances defect detection.

Spectral modifications are sensitive to detector angles.

Abstract

Recent developments in experiments with vibrational electron energy loss spectroscopy (EELS) have revealed spectral shape variations at spatial resolutions down to sub-atomic scale. Interpretation in terms of local phonon density of states enables their qualitative understanding, yet a more detailed analysis is calling for advances in theoretical methods. In Zeiger and Rusz, Phys. Rev. Lett. 124, 025501 (2020) we have presented a frequency resolved frozen phonon multislice method for simulations of vibrational EELS. Detailed simulations for a plane wave electron beam scattering on a vibrating hexagonal boron nitride are presented in a companion manuscript (Zeiger and Rusz, arXiv:2104.03197). Here we present simulations of vibrational EELS assuming a convergent electron probe of nanometer size and atomic size on a hexagonal boron nitride structure model with a planar defect. With a nanometer beam we observe spectral shape modifications in the presence of the defect, which are correlated with local changes of the phonon density of states. With an atomic size electron beam, we observe the same, although with better contrast. In addition, we observe atomic level contrast and sub-atomic scale spectral shape modifications, which are particularly strong for small detector collection angles.