Structure and Local Chemical Properties of Boron-Terminated Tetravacancies in Hexagonal Boron Nitride

Imaging and spectroscopy performed in a low-voltage scanning transmission electron microscope are used to characterize the structure and chemical properties of boron-terminated tetravacancies in hexagonal boron nitride. We confirm earlier theoretical predictions about the structure of these defects and identify new features in the electron energy-loss spectra of B atoms using high resolution chemical maps, highlighting differences between these areas and pristine sample regions. We correlate our experimental data with calculations which help explain our observations.

Figure 1

High resolution ADF image of a $V_{\mathrm{B}1\mathrm{N}3}$ tetravacancy in $h\text{−}\mathrm{BN}$ (left) and corresponding atomic model of the defect (right). Data acquired using 60 kV electrons at $500°\mathrm{C}$.

Figure 2

The B $K$ edge EELS signature of a tetravacancy. The two spectra are acquired from the center of the defect and near the defect, respectively. The spectra have been PCA filtered. The data were extracted from a $16\times 14$ pixel map acquired using 60 kV electrons at $600°\mathrm{C}$, with an exposure time of $0.5\mathrm{s}/\text{pix}$ and an energy dispersion of $0.1\mathrm{eV}/\text{ch}$.

Figure 3

EELS mapping of the B $K$ edge around a tetravacancy. The ADF signal acquired during the scan is shown in (a); the image has been low-pass filtered. An atomic model of the defect is overlaid in (b); the positions of the B and N atoms are marked in blue and red, respectively. PCA-filtered maps of the 191.1, 192.5, and 196 eV peaks are displayed in (c)–(e), respectively. $30\times 30$ pixel map acquired using 30 kV electrons at $500°\mathrm{C}$, with an exposure time of $0.1\mathrm{s}/\text{pix}$ and an energy dispersion of $0.05\mathrm{eV}/\text{ch}$.

Figure 4

First principles calculations of the B $K$ edge at the edge of the tetravacancy and in a bulklike region. The model used, highlighting the respecting positions and in-plane charge density distribution, is displayed above. The spatial distribution of orbitals corresponding to the peaks at 191.6 and 195.2 eV is inset.