Random but limited pressure of graphene liquid cells.

Even though many researchers have used graphene liquid cells for atomic-resolution observation of liquid samples in the last decade, no one has yet simultaneously measured their three-dimensional shape and pressure. In this study, we have done so with an atomic force microscope, for cells with base radii of 20-134 nm and height of 3.9-21.2 nm. Their inner pressure ranged from 1.0 to 63 MPa but the maximum value decreased as the base radius increased. We discuss the mechanism that results in this inverse relationship by introducing an adhesive force between the graphene membranes. Also, the sample preparation procedure used in this experiment is highly reproducible and transferable to a wide variety of substrates.