Events in Physics
"Reconstructing the lives of fast electrons: Solving the inverse problem of dynamical electron diffraction in both real and reciprocal space", Christoph T. Koch, Ulm, Germany
Christoph T. Koch
Institute for Experimental Physics, Ulm University, Ulm, Germany
Fast electrons, due to their 104-105 times stronger elastic scattering cross section with matter than X-rays or neutrons are the ideal probe for the atomic structure of nanomaterials. Single-crystal diffraction patterns can be obtained from just a few unit cells of a crystalline material, and high-resolution transmission electron microscope (HRTEM) images can be obtained from individual atoms. Unfortunately, this formidable feature of electron diffraction is generally considered a nuisance, because it makes multiple (dynamical) scattering unavoidable and often prevents a direct interpretation of the acquired data. Special experimental techniques, such as high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) or precession electron diffraction (PED), have been developed to make images and diffraction patterns more compatible with classical means of interpretation. However, the price paid for this apparent simplification of direct interpretation by averaging over many different dynamical diffracting conditions comes at the price of destroying valuable coherent information.
In this talk I will present our recent advances in utilizing the variations in HRTEM image or diffraction intensities due to dynamical electron diffraction for retrieving 3-dimensional atom positions of crystalline or amorphous objects [1,2] and to overcome the phase problem in crystallography [3].
[1] W. Van den Broek and C.T. Koch, Phys. Rev. Lett. 109 (2012) 245502
[2] W. Van den Broek and C.T. Koch, Phys. Rev. B 87 (2013) 184108
[3] C.T. Koch, arXiv:0810.3811