Ultrahigh nitrogen-vacancy center concentration in diamond

Kolarics, Sándor and Bojtor, András and Koltai, Kirstóf and Klujber, Gergely and Szieberth, Máté and Márkus, Bence Gábor and Beke, Dávid and Kamarás, Katalin and Gali, Ádám and Amirari, D and Berry, Robert and Boucher, Salime (2022) Ultrahigh nitrogen-vacancy center concentration in diamond. CARBON, 188. pp. 393-400. ISSN 0008-6223

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Abstract

High concentration of negatively charged nitrogen-vacancy (NV−) centers was created in diamond single crystals containing approximately 100 ppm nitrogen using electron and neutron irradiation and subsequent thermal annealing in a stepwise manner. Continuous-wave electron paramagnetic resonance (EPR) was used to determine the transformation efficiency from isolated N atoms to NV− centers in each production step and its highest value was as high as 17.5%. Charged vacancies are formed after electron irradiation as shown by EPR spectra, but the thermal annealing restores the sample quality as the defect signal diminishes. We find that about 25% of the vacancies form NVs during the annealing process. The large NV− concentration allows observing orientation dependent spin-relaxation times and also determining the hyperfine and quadrupole coupling constants with high precision using electron spin echo (ESE) and electron-nuclear double resonance (ENDOR). We also observed the EPR signal associated with the so-called W16 centers, whose spectroscopic properties might imply a nitrogen dimer-vacancy center for its origin.

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