Optimizing the density of nitrogen implantation for generating high-density NV center ensembles for quantum sensingFupan Feng, Wenlong Zhang, Jian Zhang, Liren Lou, Wei Zhu and Guanzhong WangEur. Phys. J. D, 73 9 (2019) 202DOI: https://doi.org/10.1140/epjd/e2019-100047-8