The APT technique involves preparing a needle-shaped specimen with a very sharp tip, typically less than 100 nanometers in radius. The specimen is placed in a high vacuum chamber and subjected to a high electric field, which causes atoms to ionize and be ejected from the tip. These ions are then accelerated towards a detector, and their time of flight is measured to determine their mass-to-charge ratio. By knowing the position and type of each ion, a 3D atomic map of the specimen can be generated.
