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The theory and application of inelastic coherence in the electron microscope


Hetaba,  Walid
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;


Schlögl,  Robert
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Hetaba, W. (2015). The theory and application of inelastic coherence in the electron microscope. PhD Thesis, Technische Universität, Wien.

In this work, two seemingly unrelated techniques, energy-loss magnetic chiral dichroism (EMCD) and energy losses by channelled electrons (ELCE), are described under the unifying principle of interferometric electron energy loss spectrometry (EELS). To this end, the theoretical formulations of interferometric EELS, ELCE and EMCD are presented. For both, ELCE and EMCD, simulations combining elastic and inelastic scattering effects are performed to discuss the influence of dynamical diffraction and beam convergence on the experimental results. Furthermore, EMCD is applied in course of a thorough TEM investigation of different Heusler alloys as well as magnetite, discussing its reliability concerning a “daily use”. The chosen materials exhibit a magnetostructural phase transition which can be investigated in-situ using EMCD gaining knowledge about the changes of the magnetic properties. Combining simulations and experiments paves the way for tailoring of the magnetic phase transition of materials for use in spintronics. The ELCE technique is applied to site-specifically investigate the change of the fine-structure as final states of different character are probed in rutile. It is shown that a combined Bloch wave and DFT simulation exhibits excellent agreement with the experimental spectra. The presented work shows that the combination of simulations of dynamical diffraction effects and electronic structure calculations is necessary to interpret results of ELCE and EMCD measurements. These techniques can be applied in future experiments to investigate for example the magnetic properties at surfaces and interfaces and to gain site-specific information about the bonding situation in crystals. Thus, they provide sophisticated means for electron microscopical analyses in fields like functional materials, spintronics and catalysis.