Least Squares Refinement of Structures from Dynamic Electron Diffraction Data

Abstract

Structure determination from X-ray and neutron diffraction data is a standard procedure. Starting with a rough model, the accurate structure is determined using a least-squares structure refinement, which is based on kinematic diffraction and in which the differences between calculated and experimental intensities are minimized. With kinematic diffraction the intensities of the reflections increase linearly with thickness. Dynamic scattering, which occurs in electron diffraction (ED), will change the intensities of all reflections with respect to each other as a function of the specimen thickness. An example of this change for Ce5Cu19P12, the example structure of this contribution, is shown in Figure 1. Therefore the kinematic refinement software can only be used for electrons in the regime where the dynamic scattering is small, which is in the case of Ce5Cu19P12 for specimen thicknesses smaller than about 7 nm. For example, we have used kinematic refinement [1] on data sets of very thin La3Ni2B2N3 (about 4 nm thick and in [100] and [110] orientations).