What APT needs#
Atom probe tomography reconstructs a material atom by atom, in three dimensions, by field-evaporating ions from a very sharp tip. That tip, the specimen, has to be a clean needle with an apex only tens of nanometres across, with the region of interest right at the end.
The preparation challenge#
You rarely start with a needle. You start with a bulk sample, a thin film or a buried feature, and you have to extract a small wedge and mount it on an APT coupon before the FIB sharpens it. Done badly, that transfer contaminates the specimen or wastes the feature you cared about.
In-situ lift-out#
A precise micromanipulator extracts the wedge inside the chamber, places it on the coupon post, and holds it while it is fixed in place, weld-free with SemGlu, to keep the contact clean. The FIB then annular-mills the mounted material down to a sharp needle.
Read how the needles are prepared next.
