Micrometer-Scale\nGraphene-Based Liquid Cells of Highly\nConcentrated Salt Solutions for In Situ Liquid-Cell Transmission Electron\nMicroscopy

In situ liquid-cell transmission microscopy has attracted\nmuch\nattention as a method for the direct observations of the dynamics\nof soft matter. A graphene liquid cell (GLC) has previously been investigated\nas an alternative to a conventional SiN<sub><i>x</i></sub> liquid cell. Although GLCs are capable of scavenging radicals and\nproviding high spatial resolutions, their production is fundamentally\nstochastic, and a significant compositional change in liquids encapsulated\nin GLCs has recently been pointed out. We found that graphene-based\nliquid cells were formed in nano- to micrometer sizes with high reproducibility\nwhen the concentration of the encapsulated aqueous salt solution was\nhigh. In contrast, when we revisited conventional fabrication methods,\nwater-encapsulated GLC was formed with low yield, and any electron\ndiffraction spots from ice were not confirmed by a cooling experiment.\nThe reason for this was the presence of intrinsic defects in the graphene,\nthe presence of which we confirmed by the etch-pit method. The shrinkage\nof a water-encapsulated cell and a decrease in the bubble area in\nan aqueous (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> solution cell\nsuggested that volatile water molecules and gas molecules can leak\nfrom the cells during the fabrication and observation processes. Further\nrevision of the conditions for the formation of liquid cells and a\nreduction in the number of intrinsic graphene defects are expected\nto lead to the provision of graphene-based liquid cells capable of\nencapsulating dilute aqueous solutions or pure water.