Impact of irradiation conditions on the magnetic field sensitivity of spin defects in hBN nano flakes

Abstract We study V B − centres generated by 25 keV helium focused ion beam (FIB) irradiation in thin (∼70 nm) hexagonal boron nitride (hBN) nanoflakes, to investigate the effect of implantation conditions on the key parameters that influence the magnetic field sensitivity of V B − quantum sensors. Using a combination of photoluminescence, optically detected magnetic resonance, and Raman spectroscopy we examine the competing factors of maximising signal intensity through larger V B − concentration against the degradation in spin coherence and lattice quality at high ion fluences. Both the V B − spin properties and hBN lattice parameters are largely preserved up to an ion fluence of 10 14 ions cm −2 , and beyond this significant degradation occurs in both. Our measurements give an inferred AC magnetic field sensitivity of ∼ 1 μ T / Hz at the optimal implantation dose. Using the patterned implantation enabled by the FIB, the V B − centres and the associated lattice damage are well localised to the implanted regions. This work demonstrates how careful selection of fabrication parameters optimises the properties of V B − centres in hBN, supporting their application as quantum sensors based in 2D materials.