# Substitutional Si impurities in monolayer hexagonal boron nitride

## TL;DR

This study reports the first direct observation of silicon atoms substituting boron vacancies in monolayer hexagonal boron nitride, combining experimental STEM imaging with DFT calculations to analyze stability and electronic properties.

## Contribution

It provides the first experimental evidence and theoretical analysis of substitutional silicon impurities in monolayer h-BN, revealing stable configurations and electronic effects.

## Key findings

- Silicon atoms fill boron vacancies in h-BN.
- Si_B^{+1} is the most stable substitutional configuration.
- Substitutional Si introduces defect levels in the band gap.

## Abstract

We report the first observation of substitutional silicon atoms in single-layer hexagonal boron nitride (h-BN) using aberration corrected scanning transmission electron microscopy (STEM). The medium angle annular dark field (MAADF) images reveal silicon atoms exclusively filling boron vacancies. This structure is stable enough under electron beam for repeated imaging. Density functional theory (DFT) is used to study the energetics, structure and properties of the experimentally observed structure. The formation energies of all possible charge states of the different silicon substitutions (Si$_\mathrm{B}$, Si$_\mathrm{N}$ and Si$_\mathrm{{BN}}$) are calculated. The results reveal Si$_\mathrm{B}^{+1}$ as the most stable substitutional configuration. In this case, silicon atom elevates by 0.66{\AA} out of the lattice with unoccupied defect levels in the electronic band gap above the Fermi level. The formation energy shows a slightly exothermic process. Our results unequivocally show that heteroatoms can be incorporated into the h-BN lattice opening way for applications ranging from single-atom catalysis to atomically precise magnetic structures.