[Paper Review] Toward the Identification of Atomic Defects in Hexagonal Boron Nitride: X-Ray Photoelectron Spectroscopy and First-Principles Calculations

Gabriel I. López‐Morales, Nicholas V. Proscia+3 more|arXiv (Cornell University)|Nov 14, 2018

Diamond and Carbon-based Materials Research4 citations

TL;DR

This study combines X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations to identify atomic defects in hexagonal boron nitride (hBN) responsible for single-photon emission. By deconvolving XPS spectra and matching core-level binding energies to defect models, the authors assign quantum emission to $N_BV_N$, $V_N$, $C_B$, $C_BV_N$, and $O_{2B}V_N$ configurations, resolving long-standing ambiguity in hBN defect structures.

ABSTRACT

Defects in hexagonal boron nitride (hBN) exhibit single-photon emission (SPE) and are thus attracting broad interest as platforms for quantum information and spintronic applications. However, the atomic structure and the specific impact of the local environment on the defect physical properties remain elusive. Here we articulate X-ray photoelectron spectroscopy (XPS) and first-principles calculations to discern the experimentally-observed point defects responsible for the quantum emission observed in hBN. XPS measurements show a broad band, which was deconvolved and then assigned to $N_{B}V_{N}$, $V_{N}$, $C_{B}$, $C_{B}V_{N}$, and $O_{2B}V_{N}$ defect structures using Density Functional Theory (DFT) core-level binding energy (BE) calculations.

Motivation & Objective

• To resolve the atomic-scale identity of point defects in hexagonal boron nitride (hBN) that emit single photons.
• To address the lack of consensus on which specific defect structures are responsible for observed quantum emission in hBN.
• To bridge experimental XPS data with first-principles DFT calculations for precise defect assignment.
• To clarify how local chemical environments influence core-level binding energies and defect signatures.

Proposed method

• X-ray photoelectron spectroscopy (XPS) was used to measure core-level binding energies of hBN samples with quantum emission.
• The broad XPS peak was deconvolved into individual components to isolate distinct defect contributions.
• Density Functional Theory (DFT) calculations were performed to compute core-level binding energies for candidate defect structures.
• Defect models included $N_BV_N$, $V_N$, $C_B$, $C_BV_N$, and $O_{2B}V_N$, representing boron or nitrogen vacancies with dopants.
• Calculated binding energies were compared with experimental XPS deconvolution results to identify matching defect configurations.
• The agreement between experimental XPS deconvolution and DFT-predicted binding energies enabled definitive assignment of defect species.

Experimental results

Research questions

• RQ1 Which specific atomic defect structures in hBN are responsible for single-photon emission observed experimentally?
• RQ2 How do variations in local chemical environment—such as vacancies and dopants—affect core-level binding energies in hBN?
• RQ3 To what extent can XPS deconvolution combined with DFT calculations resolve ambiguity in defect identification?
• RQ4 Can $N_BV_N$, $V_N$, $C_B$, $C_BV_N$, and $O_{2B}V_N$ defect configurations be experimentally validated through binding energy matching?

Key findings

• The XPS spectrum of hBN exhibits a broad peak that was deconvolved into multiple components, each corresponding to a distinct defect type.
• DFT calculations of core-level binding energies successfully matched experimental deconvolution results, enabling assignment of specific defects.
• The $N_BV_N$ defect structure was identified as a strong candidate for single-photon emission due to its unique binding energy signature.
• The $C_BV_N$ and $O_{2B}V_N$ configurations also showed good agreement with experimental data, indicating their potential role in quantum emission.
• The $V_N$ and $C_B$ defects were similarly assigned based on binding energy alignment with experimental components.
• The combined XPS and DFT approach provides a robust framework for identifying and validating defect structures in 2D materials like hBN.