High Sensitivity Spin Defects in hBN Created by High-Energy He Beam Irradiation

Recently the negatively charged boron vacancies (VB-$V_{\rm{B}}<^>{\bm{ - }}$) in hexagonal boron nitride (hBN) have been shown as spin defects that have great potential in quantum sensing. However, so far the sensitivity is limited by either photoluminescence (PL) intensity or the optically detected magnetic resonance (ODMR) contrast, and linewidth. In this work, the generation of these spin defects is demonstrated using high-energy helium ion beams, and ODMR measurements with different laser and microwave powers are performed. The spin defects generated by high-energy helium ions exhibit a high PL intensity and ODMR contrast while keeping a small linewidth, hence a good sensitivity. By comparing different fluences of helium irradiations, an optimal fluence is determined which is sufficient in creating spin defects without damaging the overall crystal lattice structure. With this optimal fluence, a high signal-to-noise ratio ODMR spectrum can be obtained with an accurate measurement of zero-field splitting frequency, and a best sensitivity as approximate to 2.55 mu T/Hz${\bm{ \approx }}2.55\ {\bf \mu }{\rm{T/}}\sqrt {{\rm{Hz}}} $. Moreover, with a focused beam, such spin defects can be created deterministically with nanometer precision.