Abstract
Porous metal-organic frameworks (MOFs) have shown wide applications in catalysis, gas storage and separation due to their highly tunable porosity, connectivity and local structures. However, the electron-beam sensitivity of MOFs makes it difficult to achieve the atomic imaging of their bulk and local structures under (scanning) transmission electron microscopy ((S)TEM) to study their structure-property relations. Here, we report the low-dose imaging of a beam-sensitive MOF, MIL-101, under a Cs-corrected STEM based on the integrated differential phase contrast (iDPC) technique. The images resolve the coordination of Cr nodes and organic linkers inside the frameworks with an information transfer of ~1.8Å. The local structures in MIL-101 are also revealed under iDPC-STEM, including the surfaces, interfaces and defects. These results provide an extensible method to image various beam-sensitive materials with ultrahigh resolution, and unravel the whole framework architectures for further defect and surface engineering of MOFs towards tailored functions.
Highlights
Porous metal-organic frameworks (MOFs) have shown wide applications in catalysis, gas storage and separation due to their highly tunable porosity, connectivity and local structures
We report a general scanning transmission electron microscope (STEM) strategy to image the beamsensitive MOFs with a high resolution and signal-to-noise ratio based on the two-dimensional (2D) integration of differential phase contrast images
The surfaces and interfaces of MIL-101 crystals can especially be visually investigated from the imaging results. These results helped us to resolve the construction of MOF crystals and provided a general method to image various beam-sensitive materials when we extended the integrated differential phase contrast (iDPC)-STEM imaging to other porous frameworks
Summary
Porous metal-organic frameworks (MOFs) have shown wide applications in catalysis, gas storage and separation due to their highly tunable porosity, connectivity and local structures. After a 2D integration, the obtained iDPC-STEM image could exhibit the detailed structures inside the MIL-101 framework (Fig. 2d).
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