Single‐orientation stitching of graphene has emerged as the predominant method for growth of large‐area, high‐quality graphene films. Particularly noteworthy is graphene grown on single‐crystalline Cu(111)/sapphire substrates, which exhibits exceptionally planar oriented stitching due to the atomically smooth substrate, facilitating the formation of continuous, high‐quality graphene monolayer. These single‐orientation stitches have conventionally been regarded as seamless with negligible defect concentrations. In this article, we present experimental observations regarding graphene grown on single‐crystalline Cu(111)/sapphire substrates. Among the graphene flakes with single‐orientation, our findings reveal two major merging behaviors: one producing the expected seamless stitching, and another unexpectedly generating structural defects that create nanoscale pathways permitting water permeation. Notably, we identify a unique merging structure—overlapped junction, in which the edge of one graphene flake overlaps and lies atop the edge of another flake, rather than forming a continuous atomic stitch. This discovery challenges the conventional anticipation of single‐orientation stitched graphene films as seamless single crystalline film, while offers unique perspective for graphene applications in molecular sieving, selective filtration membranes, and protective coatings.
Wang et al. (Sun,) studied this question.