Regensburg 2025 – scientific programme
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 15: Crystal Structure Defects / Real Structure / Microstructure
KFM 15.12: Talk
Thursday, March 20, 2025, 13:00–13:15, H9
Solving the phase problem: retrieving complex structure factors using Large-Angle Rocking-Beam Electron Diffraction — •Sam Fairman1, Grigory Kornilov2, Benedikt Haas2, Zbignew Galazka3, Adnan Hammud4, Niklas Delby5, and Christoph T. Koch2 — 1Physikalisch Technische Bundesanstalt, Berlin, Germany — 2Humboldt Universität zu Berlin, Berlin, Germany — 3Leibniz-Institut für Kristallzüchtung, Berlin, Germany — 4Fritz-Haber-Institut, Berlin, Germany — 5Nion Company, Kirkland, WA, USA
X-ray crystallography phasing methods have previously been successfully applied to electron diffraction experiments. However, dynamical scattering, caused by the electron’s much larger scattering cross section, is normally viewed as a hindrance to structural determination and is mitigated, e.g. by continuous rotation or precession. Presented here is an ab-initio method that makes use of dynamical scattering to solve the phase problem directly from experimental data. A custom weighting scheme is combined with the ADAM optimizer to directly fit the complex structure factors in the Bloch-wave formalism to Large-Angle Rocking-Beam Electron Diffraction data. Our method allows for an approximate 5−fold increase in spatial resolution compared to the largest spatial frequency directly measured. This recovery of resolution is ideal for beam sensitive materials where high order diffraction data is impossible to measure. Simulated and experimental results are presented for non-centrosymmetric GaN and centrosymmetric β−Ga2O3.
Keywords: Electron diffraction; LARBED; crystallography; structure factor; ADAM