(96f) Atomic Resolution Imaging of MEL Intergrowth in 2-Dimensional MFI Nanosheets
Structural aspects such as grain boundaries, defects and surface termination of two-dimensional (2D) zeolites as compared to other 2D materials like graphene, boron nitride, transition metal dichalcogenides, black phosphorus have not been fully explored.1 Even though recent advancements in aberration-corrected transmission electron microscopy (TEM) have enabled routine atomic resolution imaging of several other 2D materials, 2D zeolites remain an exception primarily due to their lower structural stability under an electron beam.2 In contrast to indirect methods of characterization like XRD, EXAFS, STM, we use aberration corrected annular dark field scanning transmission electron microscopy (ADF-STEM) to directly image the atomic arrangement in MFI nanosheet.3,4 ADF-STEM involves scanning a focused ~ 0.8 Å size, aberration-corrected electron probe across the nanosheet. The scattered electrons transmitted through the nanosheet are collected by an annular detector to form an image. This direct method of imaging reveals that domains of MEL are intergrown with MFI framework at the atomic scale. The pattern of intergrowth is identified using a template matching algorithm over the TEM images. By comparing electron diffraction (ED) patterns with simulated ED patterns we estimate the width of MFI domains and the fraction of MEL contained within these nanosheets. We will discuss in detail, the damage rate of MFI nanosheets under electron beam, the strategies for overcoming the electron beam damage, the digital image processing algorithm employed to identify the pattern of intergrowth and the structure factor calculations for simulating reciprocal lattices for patterned MFI/MEL intergrown nanosheets.
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