Quantifying the creation of negatively charged boron vacancies in He-ion irradiated hexagonal boron nitride

A Carbone and ID Breev and J Figueiredo and S Kretschmer and L Geilen and A Ben Mhenni and J Arceri and A Krasheninnikov and M Wubs and AW Holleitner and A Huck and C Kastl and N Stenger, PHYSICAL REVIEW MATERIALS, 9, 056203 (2025).

DOI: 10.1103/PhysRevMaterials.9.056203

Hexagonal boron nitride (hBN) hosts luminescent defects possessing spin qualities compatible with quantum sensing protocols at room temperature. Vacancies, in particular, are readily obtained via exposure to high- energy ion beams. While the defect creation mechanism via such irradiation is well understood, the occurrence rate of optically active negatively charged vacancies (V-B) is still an open question. In this work, we exploit focused helium ions to systematically create optically active vacancy defects in hBN flakes at varying densities. By comparing the density-dependent spin splitting measured by magnetic resonance to calculations based on a microscopic charge model, in which we introduce a correction term due to a constant background charge, we are able to quantify the number of V-B defects created by the ion irradiation. We find a lower bound for the fraction (0.2%) of all vacancies in the optically active, negatively charged state. Our results provide a protocol for measuring the creation efficiency of V-B , which is necessary for understanding and optimizing luminescent centers in hBN.

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