Atomic-resolution
scanning transmission electron microscopy (STEM)
can be used to determine the location and state of heteroatom species
in zeolites, which is essential for understanding their catalytic
behavior. However, because of the complexity of zeolite structures
and low heteroatom content, STEM images must be carefully interpreted
to avoid misidentification. In this work, Fe-doped silicalite-1 was
used as an example to illustrate this problem by combining STEM image
simulation and experiments. Simulation results indicated that, unless
the specimen has only one unit cell thickness, it is impossible to
reliably identify Fe atoms in a zeolite framework using high-angle
annular dark-field STEM (HAADF-STEM). Experimental HAADF-STEM images
could not distinguish Fe-doped silicalite-1 and Fe-free silicalite-1
samples, thus confirming the infeasibility of using HAADF-STEM to
determine the preferential occupancy of Fe between different crystallographic
sites. It was also found that integrated differential phase contrast
STEM (iDPC-STEM) could detect extraframework Fe species located in
microporous channels only when the physically adsorbed volatile organic
compounds were properly removed before imaging. The findings of this
investigation provide important precautions and guidance for related
research work.
Whether the atomic arrangement has a long-range order bifurcates solid-state matter into two major categories: crystalline and amorphous, between which lies short-range order, a frontier research topic of fundamental and...
ToTEM, a multislice‐based image simulation software is developed for transmission electron microscope (TEM). This software implements the following major features: (i) capability of assigning three‐dimensional potentials of atom into multiple slices and precise introduction of phase shift caused by the sub‐pixel atomic position, (ii) employing CUDA coding and graphical processing units (GPU) with multithreading parallel algorithm based on the powerful batch (inverse) fast Fourier transform (FFT), which is especially beneficial for image simulation of scanning transmission electron microscopy (STEM) or (integrated) differential phase contrast (I)DPC, (iii) design for efficiently generating large batch of data set of high‐resolution transmission electron microscopy (HRTEM) images. Image simulation acceleration for STEM has been verified by simulating a large‐scale SrTiO3. Additionally, iDPC image of MFI‐type zeolites with xylene molecules encapsulated in straight channels demonstrates the advantage of iDPC in detecting light molecules.
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