▎ 摘　　要

Atomically thin single crystals, without grain boundaries and associated defect clusters, represent ideal systems to study and understand intrinsic defects in materials, but probing them collectively over large area remains nontrivial. In this study, the authors probe nanoscale mass transport across large-area (approximate to 0.2 cm(2)) single-crystalline graphene membranes. A novel, polymer-free picture frame assisted technique, coupled with a stress-inducing nickel layer is used to transfer single crystalline graphene grown on silicon carbide substrates to flexible polycarbonate track etched supports with well-defined cylindrical approximate to 200 nm pores. Diffusion-driven flow shows selective transport of approximate to 0.66 nm hydrated K+ and Cl- ions over approximate to 1 nm sized small molecules, indicating the presence of selective sub-nanometer to nanometer sized defects. This work presents a framework to test the barrier properties and intrinsic quality of atomically thin materials at the sub-nanometer to nanometer scale over technologically relevant large areas, and suggests the potential use of intrinsic defects in atomically thin materials for molecular separations or desalting.