Framework for engineering of spin defects in hexagonal boron nitride by focused ion beams

Abstract: 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 (VB-) defect, which is typically fabricated by ion irradiation. However, VB- fabrication methods often lack robustness and reproducibility when applied to thin flakes (less than 10 nm) of hBN. Here we identify mechanisms that both promote and inhibit VB- generation and optimize ion beam parameters for site-specific fabrication of optically active VB- centers. We emphasize conditions accessible by high resolution focused ion beam (FIB) systems, and present a framework for VB- fabrication in hBN flakes of arbitrary thickness for applications in quantum sensing and quantum information processing.