Soft Matter and electron sensitive materials

One of the research lines at the Advanced Microscopy Laboratory relies on the study and development of multiple approaches for the observation of porous solids. Nanoporous materials, commonly zeolites (pore size below 2 nm), mesoporous materials (pore size ranging from 2 to 50 nm) and metal organic framework (MOF) solids, which consist of metal ions or clusters coordinated to organic molecules have displayed countless applications in fields such as petroleum refining and petrochemistry, drug delivery systems, water/air treatment or gas storage materials.

All these properties rely on the exploitation of the intracrystalline pore network and on the introduction and location of guest elements within the framework systems. In many cases, due to the complexity of the structures formed in addition to the high degree of information required (up to atomic level) electron microscopy is the only method powerful enough for the characterization of these nanostructures. The main drawback for the observation of these materials has been the extremely high beam sensitivity of these solids in the electron microscope. In our laboratory we have successfully controlled the microscope conditions in STEM mode which combined with the spherical aberration corrector and obtained truly atomic resolution images of several materials.

The following example illustrates these capabilities: the Fe single atomic sites in the MFI framework have been imaged for the first time. These works combined image analysis, electron diffraction and DFT calculations for providing essential structural keys in order to tune catalytically active sites at the atomic level.

Figure caption: Left: ABF data of the sodalite cage. Right: Atomic-resolution analysis of Iron containing MFI zeolite.

Reference: Direct Atomic-Level Imaging of Zeolites: Oxygen, Sodium in Na-LTA and Iron in Fe-MFI. Mayoral A.*, Zhang Q., Zhou Y., Chen P., Ma Y., Monji T., Losch P., Schmidt W., Schüth F., Hirao H., Yu J., Terasaki O. Angew. Chem. Int. Ed. 59, 19510-19517. 2020