APT involves sharpening a specimen into a needle-like shape with a tip radius of about 50 to 100 nanometers. This needle is then placed in an ultra-high vacuum chamber and exposed to a strong electric field. Atoms are ionized and ejected from the specimen's surface, typically through a process called field evaporation. These ions are then accelerated towards a detector, where their time-of-flight and impact positions are measured. The data collected allows scientists to reconstruct a 3D image of the specimen at the atomic level.
