Atomic structure and defect dynamics of monolayer lead iodide nanodisks with epitaxial alignment on graphene

Lead Iodide (PbI₂) is a large bandgap 2D layered material that has potential for semiconductor applications. However, atomic level study of PbI₂ monolayer has been limited due to challenges in obtaining thin crystals. Here, we use liquid exfoliation to produce monolayer PbI₂ nanodisks (30-40 nm in diameter and > 99% monolayer purity) and deposit them onto suspended graphene supports to enable atomic structure study of PbI₂. Strong epitaxial alignment of PbI₂ monolayers with the underlying graphene lattice occurs, leading to a phase shift from the 1 T to 1 H structure to increase the level of commensuration in the two lattice spacings. The fundamental point vacancy and nanopore structures in PbI₂ monolayers are directly imaged, showing rapid vacancy migration and self-healing. These results provide a detailed insight into the atomic structure of monolayer PbI₂, and the impact of the strong van der Waals interaction with graphene, which has importance for future applications in optoelectronics.