TEM breakthrough for complex crystals
TEM image of the metal–organic framework ZIF-8 with a structural model overlaid showing zinc ions and organic ligands (colour). [KAUST]
A team of researchers from Saudi Arabia, China and the US have adapted high resolution TEM to image the surface and interfacial structures of an intricate metal-organic framework.
Crystalline and porous 3D metal-organic frameworks (MOFs) can be designed to have precise pore sizes and large void sizes, offering huge potential in gas storage and separation, ion conduction and catalysis application.
But imaging local structures with sufficiently high resolution isn't easy due to the extreme instablity of MOFs under electron beam irradiation.
Given this, Professor Yu Han from King Abdullah University of Science and Technology and colleagues used a Gatan K2 direct-detection electron-counting camera to acquire low-dose TEM images of ZIF-8 crystals, MOFs comprising zinc ions connected by organic 2-methylimidazole linkers.
Using the Gatan detector with an uncorrected FEI Titan 80-300 electron microscope, the researchers were able to image the structure of the ZIF-8 crystals to 2.1 Angstrom, a resolution high enough to image individual columns of zinc atoms and organic linkers.
According to the researchers, TEM also revealed critical local structural features that couldn't be identified using diffraction methods.
“The results revealed that porosity generated at the interfaces of ZIF-8 crystals is different from the intrinsic porosity of ZIF-8, which influences how gas molecules transport in ZIF-8 crystals,” explains Han.
This work lays the foundations for the use of non-destructive atomic-level HRTEM imaging of other materials, including polymers and two-dimensional materials.
The research team comprised researchers from KAUST as well as Gatan, Lawrence Berkeley National Laboratory and Xi’an University of Science and Technology.
Research is published in Nature Materials.