WEB Correlative 3D characterization of hierarchical zeolite structures linking laboratory nano X-ray tomography and 360° electron tomographyWednesday (01.01.2020) 00:15 - 00:30 Part of:
The combination of 360° electron tomography (ET) with lab-based nano X-ray tomography (Nano-CT) featuring Fresnel Zone Plate and Zernike Phase ring optics allows three-dimensional (3D) imaging of complex material structures across multiple length scales. Here, we investigate MFI-type zeolite particles with sizes of up to 3 µm, which feature a network of interconnected macropores . The porous framework with its high specific surface area and interconnected pore system provides an ideal model system to demonstrate the advantages of both techniques. Combined ET and Nano-CT enables a detailed investigation of single particles as well as extended particle agglomerates regarding their intra- and interparticle pore space .
A FEI Titan Themis 300 at 300 kV in high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) mode is used for for ET experiments, which is better suited for the analysis of single particles due to its higher resolution down to a few nm. However, ET is limited to sample volumes of a few microns. Nano-CT, on the other hand, is ideally suited to analyze larger samples like particle clusters with a maximum field of view (FOV) of 64 µm and a spatial resolution of down to 50 nm in a Zeiss Xradia 810 Ultra in phase-contrast mode. The preparation of samples with one or two particles on top of the tip plateau suitable for both techniques was conducted using the particle stamping transfer technique by individually selecting and transferring particles to the top of tailormade tips in a scanning electron microscopy (SEM) instrument .
Applying Nano-CT and 360°-ET to the same zeolite sample allows to directly compare them regarding their 3D reconstruction performance with respect to a macroporous material of rather low density. Both techniques allow the reconstruction and analysis of the intraparticle macropores. Moreover, the ET dataset with its higher 3D reconstruction fidelity can serve as input for an improved segmentation of the Nano-CT data. Large FOV Nano-CT enables the analysis of larger particle agglomerates (Fig. 2), thereby enhancing the statistical relevance of the derived pore characteristics of the intra- and interparticle pore space. The derived pore size distributions from both ET and Nano-CT in Fig. 3 show an agreement for the determined pore sizes of the internal macropores with a clear peak in between 200 nm and 400 nm.