# Creation of single vacancies in hBN with electron irradiation

## TL;DR

This study measures how electron irradiation creates single vacancies in monolayer hBN, revealing lower damage rates at certain energies and proposing a theoretical model for defect engineering at the atomic level.

## Contribution

It provides the first quantitative analysis of vacancy creation in hBN via electron irradiation and introduces a theoretical model considering inelastic scattering effects.

## Key findings

- Damage rates are significantly lower below 80 keV in ultra-high vacuum.
- Single vacancies can be reliably created with electron irradiation at specific energies.
- Elastic knock-on cannot fully explain the observed damage, highlighting inelastic effects.

## Abstract

Understanding electron irradiation effects is vital not only for reliable transmission electron microscopy characterization, but increasingly also for the controlled manipulation of two-dimensional materials. The displacement cross sections of monolayer hBN are measured using aberration-corrected scanning transmission electron microscopy in near ultra-high vacuum at primary beam energies between 50 and 90 keV. Damage rates below 80 keV are up to three orders of magnitude lower than previously measured at edges under poorer residual vacuum conditions where chemical etching appears to have been dominant. Notably, is possible to create single vacancies in hBN using electron irradiation, with boron almost twice as likely as nitrogen to be ejected below 80 keV. Moreover, any damage at such low energies cannot be explained by elastic knock-on, even when accounting for vibrations of the atoms. A theoretical description is developed to account for lowering of the displacement threshold due to valence ionization resulting from inelastic scattering of probe electrons, modelled using charge-constrained density functional theory molecular dynamics. Although significant reductions are found depending on the constrained charge, quantitative predictions for realistic ionization states are currently not possible. Nonetheless, there is potential for defect-engineering of hBN at the level of single vacancies using electron irradiation.