Direct imaging of single atoms or molecules on/inside low-dimensional nanomaterials has been significantly progressed owing to the recent development of an aberration corrected electron microscopy. Anionic-charged two-dimensional (2D) clay mineral nanosheets were used in this study as a host material to build a supramolecular 2D assembly of cationic guests via electrostatic interaction, which were successfully characterized by spectroscopic techniques. For deeper understanding of clay-based supramolecular chemistry, direct imaging of the clay nanosheet and its molecular complexes in atomic-scale is the key issue. However, atomic-scale imaging of the clay nanosheet and its molecular complexes by electron microscopy has not been achieved, since clay minerals are typically sensitive to an electron beam irradiation.<br/>Here, the first atomic-scale imaging of a free-standing monolayer clay mineral nanosheet by annular dark field (ADF) imaging on aberration-corrected scanning transmission electron microscope (STEM) is demonstrated. ADF−STEM measurement was conducted at an acceleration voltage of 300 kV using a FEI Titan Cubed G2. STEM samples were prepared by dropping a solution containing well-dispersed aqueous suspension of the montmorillonite (MMT, Figure) nanosheet onto a carbon-coated Cu grid. The monolayer MMT nanosheet was stably observable under the optimum conditions, while typical bulk clay minerals are highly sensitive to an electron beam irradiation during the electron micrography. Moreover, to understand the stability of monolayer MMT nanosheet during the electron beam irradiation, we analyzed the decrease of Selected Area Electron Diffraction (SAED) intensity with TEM mode which showed the higher stability of monolayer than stacked tri-layers.

Atomic-scale imaging of a free-standing monolayer clay mineral nanosheet by aberration-corrected scanning transmission electron microscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.