Success is Not Guaranteed — Practical Matters for Direct Phase Determination in Electron Crystallography

Abstract

The success of direct phasing methods for solving crystal structures from electron diffraction intensity data is not only determined by the adherence of the observed intensities to the single scattering approximation. While manipulation of experimental parameters such as crystal thickness (minimum) and electron wavelength (also minimum) are desirable goals, there have been successful determinations based on data collected at just 50 kV. The type of preparation also has a role to play in the collection of intensity data adequate for ab initio structure analyses. For example, is the area irradiated a 1 mm diameter instead of a 1 nm diameter? The former case might minimize some dynamical interactions due to averaging over many crystal orientations while the latter might emphasize the multiple scattering component if the effective sample is a perfect flat crystal.