No 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.

The crystallographic pore sizes of zeolites are substantially smaller than those inferred from catalytic transformation and molecular sieving capabilities, which reflects flexible variation in zeolite opening pores. Using in situ electron microscopy, we imaged the straight channels of ZSM-5 zeolite with benzene as a probe molecule and observed subcell flexibility of the framework. The opening pores stretched along the longest direction of confined benzene molecules with a maximum aspect change of 15%, and the Pnma space group symmetry of the MFI framework caused adjacent channels to deform. This compensation maintained the stability and rigidity of the overall unit cell within 0.5% deformation. The subcell flexibility originates mainly from the topologically soft silicon-oxygen-silicon hinges between rigid tetrahedral SiO 4 units, with inner angles varying from 135° to 153°, as confirmed by ab initio molecular dynamics simulations.

Identifying the atomic structures of porous materials in spatial and temporal dimensions by (scanning) transmission electron microscope ((S)TEM) is significant for their wide applications in catalysis, separation and energy storage. However, the sensitivity of materials to electron beams made it difficult to reduce the electron damage to specimens while maintaining the resolution and signal‐to‐noise ratio. It is therefore still challenging to capture multiple images of the same area in one crystal to image the temporal changes of lattices. Usings integrated differential phase contrast (iDPC) STEM, atomic‐resolution imaging of beam‐sensitive zeolite frameworks is achieved with an ultralow dose of 40 e− Å−2, 2–3 orders of magnitude lower than that of conventional STEM. Based on the iDPC technique, not only the atomic 3D architecture of ZSM‐5 crystals but also the changes of frameworks are observed during in situ experiments. Local structures and light‐element aromatics in ZSM‐5 crystals can also be revealed directly under iDPC‐STEM. These results provided not only an efficient tool to image beam‐sensitive materials with ultralow beam current but also a new strategy to observe and investigate the hydrocarbon pools in zeolite catalysts at the single‐molecule scale.

We report on observations of a correlation between the microstructure of organic thin films and their electronic properties when incorporated in field-effect transistors. We present a simple method to induce enhanced grain growth in solution-processed thin film transistors by chemical modification of the source-drain contacts. This leads to improved device performance and gives a unique thin film microstructure for fundamental studies concerning the effect of structural order on the charge transport. We demonstrate that the 1∕f flicker noise is sensitive to organic semiconductor thin film microstructure changes in the transistor channel.