Optimization of carbon irradiation parameters for creating spin defects in hexagonal boron nitride

Negatively charged boron vacancy (VB−) spin defects are stable in nanoscale hexagonal boron nitride (hBN) flakes, which can be easily integrated into two-dimensional materials and devices to serve as both sensors and protective materials. Ion irradiation is frequently employed to create VB− spin defects in hBN. However, the optimal ion irradiation parameters remain unclear, even though they play a crucial role in determining the depth and density of the defects, which in turn affect sensing sensitivity. In this work, we optimize the carbon ion irradiation parameters for creating VB− spin defects by varying the irradiation dose and the incident angle. For 30 keV carbon ion irradiation, the optimal irradiation dose to create a VB− ensemble is determined to be 4 × 1013 ions/cm2, and both continuous and pulsed optically detected magnetic resonance measurements are used to estimate the magnetic sensitivity and spin coherence properties. Moreover, the incident angle of energetic ions is found to influence both the depth and density distributions of the VB− ensemble, a factor that is often overlooked. These results pave the way for improving the performance of quantum sensors based on hBN spin defects by optimizing the irradiation parameters.