Enhanced magnetic field sensitivity of shallow NV$^-$ ensembles via high-temperature implantation

Dense and shallow ensembles of negatively charged nitrogen-vacancy centers (NV$^-$) with good optical and spin properties play a key role in the performance enhancement of diamond-based quantum sensors. Ion implantation enables precise control of NV$^-$ depth and density. However, at high ion fluence, this method is limited by low NV$^-$ creation yields and sample amorphization. Additionally, shallow NV$^-$ spin properties deteriorate due to surface proximity. In this paper, we study N$_2^+$ ion implantation at energies between 10 and 15 keV with fluences as high as 1e15 ions/cm2 at temperatures of 20, 400 and 800°C to investigate the influence of implantation temperature on lattice damage, NV$^-$ creation yield and NV$^-$ spin properties. Our results show that diamond maintains structural integrity at 800°C with fluences up to 1e15 ions/cm2 without amorphization. Furthermore, high-temperature implantation improves NV$^-$ creation yields up to five times without compromising T2$^*$, T2 and T1, making it a promising approach to enhance the magnetic field sensitivity of NV$^-$ ensembles.