Three-dimensional inhomogeneity of zeolite structure and composition revealed by electron ptychography

Abstract

Structural and compositional inhomogeneity is common in zeolites and considerably affects their properties. Thickness-limited lateral resolution, lack of depth resolution, and electron dose-constrained focusing limit local structural studies of zeolites in conventional transmission electron microscopy (TEM). We demonstrate that a multislice ptychography method based on four-dimensional scanning TEM (4D-STEM) data can overcome these limitations. Images obtained from a ~40-nanometer-thick MFI zeolite exhibited a lateral resolution of ~0.85 angstrom that enabled the identification of individual framework oxygen (O) atoms and the precise determination of the orientations of adsorbed molecules. Furthermore, a depth resolution of ~6.6 nanometers allowed probing of the three-dimensional distribution of O vacancies, as well as the phase boundaries in intergrown MFI and MEL zeolites. The 4D-STEM ptychography can be generally applied to other materials with similar high electron-beam sensitivity.

Applications of Transmission Electron Microscopy in Phase Engineering of Nanomaterials

“…The advantages of 4D-STEM ptychography were clearly demonstrated in recent studies on zeolite and MOF structures. ,− For example, Zhang et al acquired 4D-STEM data for zeolites using relatively low electron doses (3000–4000 e – /Å 2 ) and performed ptychography reconstruction using an iterative algorithm that incorporated the multislice method . The reconstructed ptychographic image displays subangstrom resolution (∼0.85 Å), surpassing that of the iDPC-STEM image (Figure a,b), and it exhibits a perfect match with the projected structural model (Figure c).…”

“…49,177−180 For example, Zhang et al acquired 4D-STEM data for zeolites using relatively low electron doses (3000−4000 e − /Å 2 ) and performed ptychography reconstruction using an iterative algorithm that incorporated the multislice method. 49 The reconstructed ptychographic image displays subangstrom resolution (∼0.85 Å), surpassing that of the iDPC-STEM image (Figure 12a,b), and it exhibits a perfect match with the projected structural model (Figure 12c). This unparalleled high resolution allows not only for the clear distinction of all atomic columns, including oxygen, within the zeolite framework but also for the differentiation between coexisting MFI and MEL zeolite domains (Figure 12d).…”

“…Remarkably, this outcome was achieved using a 30-nm-defocused electron beam probe, rather than a precisely focused one. Furthermore, the ptychographic reconstruction provides a depth resolution of ∼6.6 nm, thereby revealing the 3D intergrowth of MFI and MEL zeolites that have similar structural topologies …”

“…Furthermore, the ptychographic reconstruction provides a depth resolution of ∼6.6 nm, thereby revealing the 3D intergrowth of MFI and MEL zeolites that have similar structural topologies. 49 In addition to the advantages discussed above, ptychography reconstruction also has the capability to correct a variety of imperfections in imaging, including scan shift, specimen drift, and zone-axis deviation. 181−184 As an emerging technology in electron microscopy imaging, 4D-STEM ptychography holds substantial promise for the phase engineering of nanomaterials.…”

“…EELS uncovers the surface plasmon resonances of an FCC-2H-FCC Au heterostructure . 4D-STEM enables the acquisition of multiple images with one data set, including but not limited to ADF, iCOM, and ptychography (Ptycho) . Reproduced with permission from ref , copyright 2020 Springer Nature; ref , copyright 2022 Wiley-VCH; ref , copyright 2021 Wiley-VCH; and ref , copyright 2023 American Association for the Advancement of Science.…”