Oxygen-stabilized triangular defects in hexagonal boron nitride

S. P. Huber, E. Gullikson, R. W. E. van de Kruijs, F. Bijkerk, and D. Prendergast

Phys. Rev. B 92, 245310 – Published 29 December 2015

Abstract

Recently several experimental transmission electron microscopy (TEM) studies have reported the observation of nanoscale triangular defects in mono- and multilayer hexagonal boron nitride ( $h$ -BN). First-principles calculations are employed to study the thermodynamical stability and spectroscopic properties of these triangular defects and the chemical nature of their edge termination. Oxygen-terminated defects are found to be significantly more stable than defects with nitrogen-terminated edges. Simulated x-ray absorption spectra of the boron $K$ edge for oxygen-terminated defects show excellent agreement with experimental x-ray absorption near-edge spectroscopy (XANES) measurements on defective $h$ -BN films with oxygen impurities. Finally, we show that the structural model for oxygen defects in $h$ -BN as deduced from the simulated core-level spectroscopy is intrinsically linked to the equilateral triangle shape of defects as observed in many recent electron microscopy measurements.

Received 27 August 2015
Revised 10 December 2015

DOI:https://doi.org/10.1103/PhysRevB.92.245310

Authors & Affiliations

S. P. Huber^1,2,*, E. Gullikson³, R. W. E. van de Kruijs², F. Bijkerk², and D. Prendergast¹

¹Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
²Industrial Focus Group XUV Optics, MESA + Research Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
³Center for X-Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^*shuber@lbl.gov

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Vol. 92, Iss. 24 — 15 December 2015

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Images

Figure 1
Partial images of $h$ -BN crystalline supercell including triangular defect with four out of six different edge terminations investigated in this study: (a) electron-doped nitrogen-terminated $V_{B_{10} N_{6}}^{N:e}$ , (b) hydrogen-passivated nitrogen-terminated $V_{B_{10} N_{6}}^{N:H}$ , (c) oxygen-terminated $V_{B_{10} N_{6}}^{O}$ , and (d) boron-terminated $V_{B_{6} N_{10}}^{B}$ . The structures shown are all relaxed under neutral charge conditions with the exception of the nitrogen-terminated case, where one electron was added for each undercoordinated edge atom. Hydrogen, nitrogen, boron, and oxygen atoms are colored pink, light blue, green, and red, respectively (or from lightest to dark gray in the same order).
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Figure 2
Top view of part of the surface plane of the $V_{B_{3} N_{1}}^{N}$ supercell model for the (a) neutral and (c) charged supercell surface slab model. The side views (b) and (d) correspond to the top two layers of the neutrally and negatively charged slab, respectively, with the rightmost plane being the surface plane. The dashed lines indicate the unperturbed crystal lattice.
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Figure 3
(a) Measured and simulated x-ray absorption spectrum of the boron $K$ edge in $h$ -BN. The dotted black line is the measured spectrum for the 13-nm thin film on the Cu(111) substrate. The simulated spectra for the static structure at $T = 0$ K and the thermally equilibrated structure are shown in a dashed gray and solid red line, respectively. (b) Closeup of main $π^{*}$ and three satellite features indicated by arrows. (c) Top and (d) side view of a $5 \times 5 \times 1 h$ -BN supercell with an isosurface representation of the squared wave function $| ψ (\vec{r}) |^{2}$ of the excitonic state corresponding to the intense transition in the B $K$ -edge spectrum at 192 eV. The excitonic state is highly localized and has distinct antibonding $p$ -like character.
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Figure 4
(a–c) Schematic representation of the ${BN}_{3 - x} O_{x} (1 \leq x \leq 3)$ substitutional oxygen defect environments of boron atoms in $h$ -BN. (d–f) Defect structures in a $h$ -BN host crystal that hosts a boron atom with ${BN}_{2} O, {BNO}_{2}$ , and ${BO}_{3}$ environment, respectively, while maintaining twofold coordination for the oxygen atoms and threefold coordination for nitrogen and boron atoms. The colors of the circles around selected boron atoms correspond to spectra in Fig. 5.
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Figure 5
Measured and simulated B $K$ -edge x-ray absorption spectra for hexagonal boron nitride. The solid black line corresponds to the measured spectrum for multilayer $h$ -BN on a $Cu (111)$ substrate and the dashed gray line is the thermally averaged simulation. The four colored spectra with the first peak increasing from lower to higher energy represent the simulated spectrum of a single boron atom with a local ${BN}_{3}, {BN}_{2} O, {BNO}_{2}$ , and ${BO}_{3}$ environment, respectively. The labels $π_{0}^{*} – π_{3}^{*}$ and corresponding vertical dashed lines denote the energy position of the main $π^{*}$ and satellite peaks as observed in experiment.
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