Acquiring precession-assisted 4D STEM data via pure software control in DigitalMicrograph

Gatan instruments used

STEMx^® Precession, STEMx system, ClearView^® camera, and DigitalMicrograph^® software

Background

4D STEM is an incredibly useful technique for collecting high spatial resolution diffraction information from a sample. The data can be analyzed to generate virtual images, strain maps, orientation maps, and more. One challenge, especially with strain and orientation mapping, can come from dynamical diffraction effects that degrade data quality and analytical results. For example, significant contrast variation within diffraction disks, forbidden reflections from multiple scattering, and large inelastic scattering backgrounds may all negatively affect analysis. 
 

Precession electron diffraction offers a strategy for reducing these deleterious dynamical diffraction effects and generating a more quasi-kinematical diffraction pattern to improve analytical results [1]. By applying a beam tilt (f) and precessing the beam around the optical axis during pattern acquisition, the resulting pattern will feature more even disk contrast, minimize contributions from multiple scattering, and include higher order spots with better signal to noise. Furthermore, combining precession methods with 4D STEM can improve the 4D STEM diffraction pattern and yield improved analysis results.