Alignment

Automatic transmitted beam fitting

When a 4D-STEM dataset is first imported, Quant4D will attempt to find the transmitted beam using the mean diffraction pattern from all probe positions. This is done using a circular Hough transform, giving preference to the strongest circular feature nearest the center of the diffraction pattern. If this routine fails outright or incorrectly fits the transmitted beam, the user can manually fit the transmitted beam using either an interactive circular annotation on the diffraction pattern, slider bars, or numerical inputs (x, y, radius). All of these UI elements are linked and update automatically.

Additionally, a routine is provided for aligning the transmitted beam to the intersection of two lines. The user can press the X button in the Transmitted Beam Position Alignment panel of the Main Window. The circular annotation will then be linked to the intersection of two line annotations, which can be interactively moved by the user to correspond, for example, to Kikuchi lines or a row of diffraction spots.

Tip: to better see details in the diffraction pattern, use the brightness/contrast/gamma controls in the Display tab of the Settings window.

Diffraction scale

Quant4D can be calibrated in diffraction space by fitting the transmitted beam and reporting a known probe convergence angle in mrad, or by simply reporting a known scale in mrad/pixels, which is then propagated through the rest of the GUI for all detectors and masks generated.