Advances in Quantification and Resolution in Electron Tomography
Zusammenfassung der Projektergebnisse
Within this project we developed HACDF TEM tomography as a complementary technique to HAADF-STEM for Z-contrast imaging. For that we investigated the limitations, employed the necessary procedure and have shown that the resolution of HACDF and HAADF are comparable. Depth-sectioning in the TEM mode was investigated as an additional method to obtain three-dimensional data on the atomic scale. The depth-of-field for the CS aberration corrected microscope was measured experimentally and validated by image simulations. It was shown for the case of Si nanoparticles within SiO2 that they can be atomically resolved. During the period of this project we introduced the 360° tomography acquisition experimentally by specific sample preparation with a focused-ion-beam machine. Thus, we could minimize the effect of the missing-wedge. Moreover, we studied a Raney-type Ni catalytically particle by FIB-tomography enabling specific alignment procedures and extensive three-dimensional visualization in order to solve material-related questions in 3D. As correct binarization evolved to be essential for reliable quantification of data obtained by electron tomography, we studied various effects by simulation and derived a binarization model. We have shown that the described methodology is inevitable for future developments in 3D quantification and have shown that neither global nor local thresholding representing standard practiced schemes are sufficient. Instead anisotropic schemes similar to the developed ones have to be applied. However, for the application to different material systems further development is necessary. With respect to further advances in electron tomography, we have shown for the first time the experimental acquisition of carbonaceous material at low voltage for 3D evaluation. We could reveal, for the case of a carbon soot particle with catalytically active platinum particles, interesting features from the inner structure; however, further development is necessary.
