The structure of an aluminosilicate ITQ-39 has been determined by electron crystallography, it is one of the most complex zeolite ever solved [1]. ITQ-39 has a 3-dimensional channel system with intersecting 10- and pairwise 12-ring channels. It has a highly faulted structure and contains stacking disorder along [100], twinning along [010] and point defects. High-resolution transmission electron microscope (HRTEM) images were chosen to study these disorders. In order to improve HRTEM data quality, a through-focus series of 20 HRTEM images were collected and a structure projection image was reconstructed (see Fig. 1) by a contrast transfer function (CTF) correction algorithm using the software QFocus [2]. The through-focus series was acquired with a constant focus step (-53.3 Å) and the two-fold astigmatism was the same through the series. Defocus values and the two-fold astigmatism were then determined for all the images. CTF correction was performed on each image and the final reconstructed image was obtained by averaging all 20 CTF-corrected images (see Fig. 1b). Defocus determination revealed that the image series passed through the Scherzer focus condition and contained at least one image close to the Scherzer condition (Fig. 1a). By using structure projection reconstruction the noise in the images was significantly reduced and the structure and pore system were more obvious after the reconstruction. One big advantage is that there is no need to spend time to adjust to a certain focus (e.g. close to Scherzer focus), therefore the acquisition of HRTEM images can be done much faster which is very useful for beam sensitive samples.

References

[1] Willhammar, T. et al. Structure and catalytic properties of the most complex intergrown zeolite ITQ-39 determined by electron crystallography. 2012, Nature Chemistry, 4 (188-194).

[2] Wan W. et al. Structure projection reconstruction from through-focus series of high-resolution transmission electron microscopy images. 2012, Ultramicroscopy, 115 (50-60).

Acknowledgements

The project is supported by the Swedish Research Council (VR), the Swedish Governmental Agency for Innovation Systems (VINNOVA) and the Knut & Alice Wallenberg Foundation through the project grant 3DEM-NATUR and a grant for purchasing the TEM.  

Figures:

Figure 1. Structure of ITQ-39 along the [010] direction, HRTEM image close to the Scherzer condition (a) and reconstructed structure projection image (b).

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