Atomic-scale imaging reveals secret to thin film strength

March 28, 2020 - A team of scientists and engineers, led by University of Minnesota Associate Professor K. Andre Mkhoyan and Professor Emeritus Michael Tsapatsis (currently, a Bloomberg Distinguished Professor at Johns Hopkins University), have made a discovery that could further advance the use of ultra-thin zeolite nanosheets, which are used as specialized molecular filters. The discovery could improve efficiency in the production of gasoline, plastics, and biofuels.

The breakthrough discovery of one-dimensional defects in a two-dimensional structure of porous material (a zeolite called MFI) was achieved using a powerful high-resolution transmission electron microscopy (TEM) on the University of Minnesota Twin Cities campus. By imaging the atomic structure of the MFI nanosheets at unprecedented detail, the researchers found that these one-dimensional defects resulted in a unique reinforced nanosheet structure that changed the filtration properties of the nanosheet dramatically.

The findings are published in Nature Materials, a peer-reviewed scientific journal.

“TEM imaging of thin zeolite crystal at the atomic-scale has been a long-standing challenge as these crystals are readily damaged under the high-energy electrons, which are needed for atomic-scale imaging,” said Mkhoyan, an expert in advanced TEM and the Ray D. and Mary T. Johnson/Mayon Plastics Chair in the Department of Chemical Engineering and Materials Science at the University of Minnesota’s College of Science and Engineering. “It requires a deep understanding of the mechanisms of beam damage for zeolite crystals and the doses of electron beam that the zeolite can take. This work pushed the limits of our electron microscopes, where we can reliably produce atomic-resolution images of such extremely thin (just 3-nanometers-thick) zeolite nanosheets with identifiable one-dimensional intergrowths.”

The minute differences between the two materials (refer to enclosed image) was detected by Prashant Kumar, a graduate in the University of Minnesota Twin Cities College of Science and Engineering, after nearly five years of research.

“I have been fascinated by the beautiful symmetrical patterns in MFI crystal throughout my Ph.D. work,” said Kumar, a lead author of the study. “After staring at noisy images in the TEM for countless hours, I finally saw the symmetry breaking in the TEM images of MFI nanosheets—I knew this was unusual.”

Members of the research team include Ph.D. students and post-doctoral fellows Prashant Kumar, Dae Woo Kim, Neel Rangnekar, Supriya Ghosh, Han Zhang, Meera Shete, and Qiang Xiao; faculty members K. Andre Mkhoyan (Department of Chemical Engineering and Materials Science), Evgenii Fetisov and Professor Ilja Siepmann (Department of Chemistry); and Hao Xu and Traian Dumitrica (Department of Mechanical Engineering); senior research associate Benjamin McCool (ExxonMobil); and professor emeritus Michael Tsapatsis (Johns Hopkins).

This research was primarily funded by the National Science Foundation, with partial support for certain characterizations and computations by the U.S. Department of Energy and a variety of University of Minnesota partners.

To read the full research paper entitled “One-dimensional intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport,” visit the Nature Materials website:

Excerpt from news release written by Rhonda Zurn, College of Science and Engineering. Read the full release via the link below.

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