ALPHABETA: a dedicated open-source tool for calculating TEM stage tilt angles.

This work describes the concepts, the mathematical framework and the implementation of the open source ALPHABETA software, a dedicated tool for calculating alpha and beta tilt angles on any TEM double tilt stage. ALPHABETA provides an intuitive user interface to calibrate the orientation of the region of interest and to subsequently calculate the angle tilts to reach a zone axis, to perform a rotation around a given reflection, or to set up a 2-beam or weak beam condition. The orientation of the sample on the stage and the tilt range reachable domain can be visualised in a stereographic projection plot. The accuracy of the method to reach a set of zone axis was evaluated and some case studies are presented. The tool significantly reduces time for tilting work as major tilts can be performed in image mode and reachable zones are beforehand indicated in the software. Besides facilitating the tilting to different zone axes, the software can be used for miscellaneous applications such as making dark field tilt series without specialised hardware.