Milos Toth

Hexagonal boron nitride (hBN) is gaining interest as a wide bandgap van der Waals host of optically active spin defects for quantum technologies. Most studies of the spin‐photon interface in hBN focus on the negatively charged boron vacancy (V B − ) defect, which is typically fabricated by ion irradiation. However, the applicability and wide deployment of V B − defects is limited by V B − fabrication methods which lack robustness and reproducibility, particularly when applied to thin flakes (≲10 nm) of hBN. Here, two key factors are elucidated that underpin the formation and quenching of V B − centers by ion irradiation—density of defects generated in the hBN lattice and recoil‐implantation of foreign atoms into hBN. Critically, it is shown that the latter is extremely efficient at inhibiting the generation of optically‐active V B − centers. This is significant because foreign atoms such as carbon are commonplace on both the top and bottom surfaces of hBN during ion irradiation, in the form of hydrocarbon contaminants, polymer residues from hBN transfer methods, protective capping layers and substrates. Recoil implantation must be accounted for when selecting ion beam parameters such as ion mass, energy, fluence, incidence angle, and sputter/span yield, which are discussed in the context of a framework for V B − generation by high‐resolution focused ion beam (FIB) systems.