A general strategy for imaging confined molecules and their interactions, applying low-dose electron microscopy techniques across multiple material systems, has been proposed by recent research published on March 14, 2025. This innovative approach aims to overcome challenges traditionally faced by electron microscopy, particularly in the thermal mobility of molecules and their sensitivity to electron beams. By utilizing low-dose imaging and confinement effects, researchers can obtain high-resolution images of molecules and their interactions within various material systems.
The findings of this study, led by the authors, encompass three significant material systems: perovskites, zeolites, and metal-organic frameworks (MOFs). Each system presents unique interaction dynamics between the host materials and the guest molecules—ionic interactions observed with perovskites, van der Waals forces within zeolites, and coordination interactions involved with MOFs.
Specifically, when investigating perovskites, the positions of FA+ molecules were successfully imaged, locating them within the ionic framework of PbI6 octahedrons. This high-precision imaging enabled the researchers to analyze the influences of different A-site cations on the resulting molecular projections. For example, the imaging results indicated varying aspect ratios, with MAPbI3 featuring aspect ratios near one, contrasting with CsPbI3, which revealed elliptical projections as host-guest interactions strengthened.
Zeolite materials, particularly ZSM-5, provided another environment for imaging, as the study successfully detailed aromatic molecule arrangements like benzene as they were confined within the zeolite's channels. Using integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM), the study illustrated how different adsorption molecules impacted the geometric configuration and visualization of molecular projections. It was found the overall aspect ratios of aromatic molecules increased progressively from furan to pyridine to benzene, as the confinement of the ZSM-5 framework improved.
Another major focus was the imaging of the atomic structures within MOFs such as UiO-66. Here, the atomic arrangements of the BDC linkers were employed, and the study established methods to not only visualize but also analyze bond lengths varying from Zr–O bonds at 2.5 Å to Ti–O bonds at 2.0 Å. This precise resolution showcases the molecular structure details achievable through enhanced confinement and imaging techniques.
Overall, the results ascertain how heightened host-guest interactions directly correlate with improved image quality. The researchers emphasized, "This work not only introduces a general confinement strategy for resolving molecular structures, but also establishes an effective evaluation method for quantitatively analyzing the interaction strengths between host and guest units during the imaging process, which may help us understand various behaviors and interactions of these molecules in the real space." This not only signifies considerable advancements within molecular imaging but also paves the way forward for prospective studies and applications across various fields.
By evaluating the aspects of confinement strength, structural coherence, and specific imaging methodologies, future research can aim at resolving even more complex molecular interactions at varying real-world conditions. With this innovative strategy, the study asserts its contribution toward achieving greater potential for direct observation of molecular behaviors and reveals pathways for applications across disparate areas ranging from catalysis to energy storage.