PPubMed1 Jan 2015Cited 7×

Solving difficult structures with electron diffraction Electron diffraction

J. M. Zuo, J. L. Rouviére

Abstract

Precession electron diffraction has solved a long-standing challenge in electron diffraction. Further progress promises a general technique for structure determination of difficult crystals.

A figure from Solving difficult structures with electron diffraction Electron diffraction — fig. from the paper

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Precession electron diffraction has solved a long‑standing challenge in electron diffraction.

What’s new

i.PED provides integrated electron diffraction intensities that are robust against crystal thickness variations and small misorientations.
ii.Using PED intensities, crystal structures can be solved with R factors reduced to less than 10% when dynamic effects are included.
iii.PED has been integrated with automated diffraction tomography (ADT) and scanning diffraction pattern indexing for quantitative crystallography.

How they did it

In precession electron diffraction (PED) the incident electron beam rotates around a crystal direction while keeping a constant precession angle; the outgoing beams are deflected back to compensate for the motion. This records integrated diffraction intensities across the Bragg condition for many reflections, which are then used for phasing and structure refinement.

What they found

R factor can be reduced to less than 10% when dynamic effects are included (Palatinus et al., 2013; Jacob et al., 2013).
Precession angle of 0.6° used in CBED patterns of Si at 200 kV (Figure 1).
Electron wavelength is a few picometers for 80–300 keV electrons.

Caveats

✕A general method for solving unknown crystal structures using dynamic diffraction intensities has not yet been developed.
✕Strong multiple scattering (dynamic diffraction) complicates structure solution.
✕Current refinement methods require a known structure.

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