3D Electron Microscopy Methods and Applications : Structures from Atomic Scale to Mesoscale

Sammanfattning: The crystal structure determines the physical properties of a material. The structure can be analysed at different levels, from atomic level, mesoscale level, all the way up to the macroscale level. Transmission Electron Microscope (TEM) is a powerful tool for studying the structure of materials at atomic scale level and mesoscale level because of the short wavelength of the electrons. At atomic scale level, structure determination using TEM can be performed in diffraction mode. The recent developments in 3D electron diffraction methods make structure determination from nano- and micron-sized crystals much easier than before. However, due to the strong interactions, electrons can be scattered multiple times through the crystal, causing the measured intensities to be less accurate than that in the X-ray case.In this thesis, we use the continuous rotation electron diffraction (cRED) developed in our group to investigate the structure of materials and the accuracy of this method. In the third chapter, we use cRED method to determine the structure of two aluminophosphate zeolites, PST-13 and PST-14. We presented that these structures can be built from two pairs of enantiomeric structural building units. In the fourth chapter, we show that despite the inaccuracy in measured intensities originated from dynamical effect, it is still possible to determine the structure accurately. We show that the atomic coordinates of ZSM-5 and sucrose crystal structure determined by multiple electron diffraction datasets is identical to that determined from X-ray data or neutron data. We also assessed the linearity between calculated structure factor and observed structure factor and use this as a coarse assessment indicator for diffraction data quality for protein crystals.Apart from atomic structure, mesoscale structures, such as mesopores, can also determine the property of materials. For the 3D structures of these nanoscale structures, we can also use TEM electron tomography techniques to investigate. In chapter five, we performed electron tomography for two different materials with mesoporous structure and illustrated the formation mechanism of mesoporous magnesium carbonate and the internal tunnel structure of hierarchical TS-1 zeolite.