4. Data Collection

Data collection for an atom probe tomography (APT) experiment is the process of (1) introducing an electric field on a specimen in order to initiate ion emission by field evaporation, (2) using the initial ion events to allow fine positioning of the specimen, and (3) increasing and adjusting the voltage (and thus the electric field) to obtain a steady rate of detected ion events. The details of how one can maneuver through these steps safely and efficiently are the focus of this chapter. Because a strong electric field is required to initiate field evaporation, the resulting forces create large stresses that act on the specimen, placing it in continual jeopardy of mechanical failure. Consequently, a successful atom probe experiment is a balancing act of minimizing the chance for specimen failure while at the same time extracting maximum quality from the collected data. After reading this chapter, it becomes clear that prioritize yield over data quality (one must have data before judgments can be made on its quality), but the ultimate decision on this issue rests with the user. Depending on the details of any particular experiment, the user may decide that either specimen yield or data quality takes precedence.