Defect Engineering of Monoisotopic Hexagonal Boron Nitride Crystals via Neutron Transmutation Doping

Abstract

The nature of point defects in hexagonal boron nitride (hBN) is of current interest for the potential to alter its optical and electrical properties. The strong interaction between neutrons and the boron-10 isotope makes neutron irradiation a controllable way to introduce point defects in hBN. In this study, we perform Raman spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and optically detected magnetic resonance (ODMR) characterization of neutron-irradiated monoisotopic (hBN with a single boron isotope) 10 Band 11 B-enriched hBN crystalline flakes and a pyrolytic BN (pBN) reference sample. In h 10 BN and pBN, neutron irradiation produced two new Raman bands at 450 and 1335 cm −1 , which could be associated with B-related vacancies or defects. The near-bandedge optical emission was also significantly impacted by the neutron irradiation. EPR measurements clarified the origin of a high-spin defect center due to negatively charged boron vacancies, which was recently reported for similar neutron-irradiated hBN crystals. The ODMR experiments further confirmed this assignment. Hightemperature annealing partially recovered some of the hBN vibrational and optical properties. Our results are helpful to identify the nature of defects in hBN and enable defect-engineered applications such as quantum information and sensing. 10 7 4

Decoherence of V$${}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ spin defects in monoisotopic hexagonal boron nitride

“…Indeed, the thermal neutron capture cross-sections of 11 B ( ~0.005 barn) and 14 N ( ~1.8 barn) are orders of magnitude smaller than that of 10 B ( ~3890 barn) 32 . As a result, neutron irradiation of the h 10 BN crystal likely creates boron vacancy-related defects through nuclear transmutation and introduces interstitial 7 Li atoms resulting from the fission of the 10 B isotope 32 , 33 . Conversely, the h 11 BN crystal is almost transparent to neutrons and point defects are solely created by neutron scattering.…”

Emitter-Optomechanical Interaction in Ultra-High-Q hBN Nanocavities

“…The other peaks are not observed in Si 3 N 4 nor non-irradiated hBN (see supplemental material), therefore identified as arising from V − B centers. Peaks r6 around 450 cm −1 (red) and r10 at 1306 cm −1 (blue) have been previously identified: r6 is the highly localized phonon and r10 is the extended phonon [32] discussed in the context of Fig. 2(a).…”

“…2(a), one may expect that extended phonons which involve the vibration of multiple atoms (blue rings) govern the trapping process, whilst more strongly localized phonons involving only the vibrations of neighboring atoms (red rings) dominate the replica process. J. Li et al [32] recently reported Raman spectroscopy of V − B centers, and unveiled this picture of Raman peaks for highly localized and extended phonons via the boron isotope characterization.…”

“…Various Raman peaks are observed and labelled r1-14 on the figure. Peaks r7 at 524 cm −1 and r9 around 975 cm −1 are the bulk Si 3 N 4 phonons [37], and r11 at 1377 cm −1 is the bulk hBN phonon E 2g [32]. The other peaks are not observed in Si 3 N 4 nor non-irradiated hBN (see supplemental material), therefore identified as arising from V − B centers.…”

Magnetic imaging with spin defects in hexagonal boron nitride

“…For magnetic imaging, we rely on a monoisotopic h 10 BN crystal grown from a Ni-Cr flux [27], which was irradiated with thermal neutrons with a dose of about 2.6 × 10 16 n/cm 2 . The interest of isotopic purification with 10 B lies in its very large neutron capture cross section, which ensures an efficiently creation of V − B centers via neutron transmutation doping [28,29]. hBN flakes mechanically exfoliated from this neutron-irradiated crystal were deposited above the CrTe 2 flakes.…”