The role of absorption in 3D electron diffraction dynamical structure refinement.

Abstract

The role of absorption in 3D electron diffraction is established through analytical theory, simulation and dynamical refinement. A two-beam expression for the absorbed integrated intensity in centrosymmetric crystals is derived, showing that for t/ξg ≪ 1 reflections follow a uniform exponential decay set by the mean absorptive potential U0'. Many-beam simulations of both centrosymmetric and non-centrosymmetric crystals reveal additional reflection-specific anomalous absorption beyond the uniform attenuation set by U0'. Neglecting these effects in dynamical refinement of integrated intensities incurs an error that increases approximately linearly with thickness, with this error becoming more severe near zone axes. Dynamical refinements were performed on CsPbBr3, quartz and borane, with the inclusion of absorption yielding an improvement in Robs from 6.4 to 5.3% for CsPbBr3, and negligible improvements for quartz and borane. Anomalous absorption may therefore be ignored for routine refinement of integrated intensities except in high-Z materials at thicknesses approaching ξg.