# Angular resolved electron energy loss spectroscopy in hexagonal boron nitride

## TL;DR

This paper introduces a novel electron energy loss spectroscopy method for hexagonal boron nitride that provides high-quality spectra and diffraction imaging, enabling detailed analysis of excitations with advantages over traditional techniques.

## Contribution

The study presents a new spectroscopic setup combining an electron microscope with a monochromator and in-column filter, enhancing the analysis of excitations in 2D materials.

## Key findings

- High-quality core loss spectra at B and N K edges were obtained.
- The method offers results comparable to non-resonant X-ray scattering with greater sensitivity and simplicity.
- Theoretical calculations help determine the applicability and accuracy of ab initio simulations.

## Abstract

Electron energy loss spectra have been measured on hexagonal boron nitride single crystals employing a novel electron energy loss spectroscopic set-up composed by an electron microscope equipped with a monochromator and an in-column filter. This set-up provides high-quality energy-loss spectra and allows also for the imaging of energy-filtered diffraction patterns. These two acquisition modes provide complementary pieces of information, offering a global view of excitations in reciprocal space. As an example of the capabilities of the method we show how easily the core loss spectra at the $K$ edges of boron and nitrogen can be measured and imaged. Low losses associated to interband and/or plasmon excitations are also measured. This energy range allows us to illustrate that our method provides results of quality comparable to those obtained from non resonant X-ray inelastic scattering, but with advantageous specificities such as an enhanced sensitivity at low q and a much higher simplicity and versatility that makes it well adapted to the study of two-dimensional materials and related heterostructures. Finally, by comparing theoretical calculations against our measures, we are able to relate the range of applicability of ab initio calculations to the anisotropy of the sample and assess the level of approximation required for a proper simulation of our acquisition method.