Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Abstract

Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure challenge their technological utility. Here, we directly correlate hBN quantum emission with local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nanobeam electron diffraction. Across 40 emitters, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540 to 720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, at least four distinct defect classes are responsible for the observed emission range, and all four classes are stable upon both optical and electron illumination. Our results provide a foundation for future atomic-scale optical characterization of colour centres.

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Fig. 1: Correlated optical and electron characterization of quantum emitters in hBN.
Fig. 2: Cathodoluminescence mapping reveals multiple and distinct quantum-emitter species within a diffraction-limited optical spot.
Fig. 3: Correlating stable emitter PL and CL spectra reveals two types of behaviour.
Fig. 4: Correlating quantum emission with local strain.
Fig. 5: Emitter classification.

Data availability

All strain analysis data presented in Fig. 5 are included in Supplementary Information. Due to large file sizes, strain mapping and all other electron microscopy source data are available from the corresponding authors on request.

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Acknowledgements

The authors acknowledge useful discussions about strain mapping with T. Pekin (Humboldt-Universität zu Berlin) and about CL–PL correlations with C. McLellan (Stanford). TEM imaging and spectroscopy were performed at the Stanford Nano Shared Facilities and Stanford Soft & Hybrid Materials Facility. The PL, TEM experiments and theoretical modelling were supported by the DOE ‘Photonics at Thermodynamic Limits’ Energy Frontier Research Center under grant no. DE-SC0019140. F.H. gratefully acknowledges the support of the Diversifying Academia, Recruiting Excellence (DARE) Doctoral Fellowship Program by Stanford University. J.V. acknowledges the support the NSF Quantum Leap EAGER grant no. DMR 1838380. T.F.H. and L.Y. also acknowledge support from the Betty and Gordon Moore Foundation EPiQS Initiative through grant no. GBMF4545.

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Contributions

F.H., L.Y., T.F.H. and J.A.D. conceived the project. F.H. made the samples and performed the PL and TEM experiments. J.L.Z., L.Y. and F.H. performed the second-order correlation measurements under the supervision of J.V. C.J.C. and P.N. performed the theoretical calculations. A.F.M. assisted in strain map data collection. M.N. and I.A. assisted in sample preparation. F.H. and J.A.D. wrote the draft. J.A.D. supervised the project. All co-authors discussed the results and provided useful feedback on the manuscript.

Corresponding authors

Correspondence to Fariah Hayee or Jennifer A. Dionne.

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Extended data

Extended Data Fig. 1 Higher energy lines associated with the 580-590 nm emitters.

a, HAADF and decomposed CL spectral weight maps of the emitter with ZPL at 578 nm in Fig. 4a of main text. b, CL spectral components showing higher energy peaks similar to that in Fig. 2a. c, HAADF and CL spectral weight maps of the emitter E6 in Fig. 3a with ZPL at 590 nm. d, CL spectral components for emitter in (c). Each pixel in the CL weight maps is 15 nm. For both emitters here, the PL spectrum has two probable phonon-sidebands, a similar spectral signature to the emitter in the main text Fig. 2a. All these three emitters have four higher energy (UV-blue) peaks in their CL spectrum. For the particular emitter in panels (c-d), spectral decomposition shows that the 420 nm emitter is located 80 nm away from the 590 nm emitter. However, the 460 nm, 500 nm and 532 nm peaks are localized to the same 15 nm bright pixel as the 590 nm peak.

Supplementary information

Supplementary Information

Supplementary Figs. 1–13 and discussion sections 1–10.

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Hayee, F., Yu, L., Zhang, J.L. et al. Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy. Nat. Mater. 19, 534–539 (2020). https://doi.org/10.1038/s41563-020-0616-9

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