Swelling and the activation of hBN single-photon emitters synthesized by focused ion beam patterning and carbon-rich annealing

Emerging quantum technologies require controlled fabrication of quantum systems in solid-state materials. Focused ion beam (FIB) has become a versatile tool to create nanostructures and single-photon emitting (SPE) defects in materials. In particular, the ability to pattern arrays of bright and stable room temperature SPEs in two-dimensional hexagonal boron nitride (hBN) via high-energy, heavy-ion FIB allows for direct placement of SPEs. However, the FIB parameters needed to create hBN SPEs are dependent on post-FIB annealing steps. Moreover, morphological damage induced by FIB exposure may further influence the successful creation of SPEs. In this work, we perform atomic force microscopy to characterize the surface morphology of hBN regions patterned by Ga+ FIB to create SPEs at a range of ion doses and find that material swelling is strongly correlated to the onset of non-zero SPE yields. Furthermore, we simulate vacancy and impurity profiles at each of the tested doses and propose a qualitative model to elucidate how Ga+ FIB patterning followed by carbon-rich annealing creates isolated SPEs that is consistent with observed optical and morphological characteristics. Our results provide novel insight into the formation of hBN SPEs created by high-energy, heavy-ion FIB that can be leveraged for monolithic hBN photonic devices and a wide range of low-dimensional solid-state SPE hosts.