Unordnung im Nanobereich: Schichtstrukturen unter dem Elektronenmikroskop
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Abstract
The solid state structure of material as a major determinant of its physical properties is often highly complex. Frequently, the order of a crystal is perturbed by a variety of defects often necessary to gain the desired property. Modern transmission electron microscopy (TEM), provides a resolution down to 0.05 nm, allowing the investigation of these important structural features using both diffraction and imaging. With the development of electron diffraction tomography (EDT) methods, a crystal structure can be determined from nano crystalline domains directly from electron diffraction intensities. With an increasing amount of disorder, this approach becomes more and more hampered.
This work presents the first systematic and quantitative disorder analysis using the total diffraction information. The extraction of diffuse scattering from the 3D diffraction space based on automated electron diffraction tomography (ADT) data was developed as a general routine applicable to one- and two-dimensional defect structures. For the model compound, zeolite beta, the ratio of intergrown polymorphs could be determined quantitatively by an automated comparison of simulated and experimental diffraction patterns. In addition to an initial structure determination of disordered single nanoparticles using reflection intensities measured by ADT, the methodical pathway developed in this work, enables an enhanced structural description of unknown nanomaterials. This approach is applied to a new class of previously unknown layer silicates (Magadiit and RUB-6) and a unique silica polymorph (RUB-5).