FIB methods rely on the use of a gallium ion (Ga⁺) beam to mill away material. This is done in a dual beam (ion/electron) microscope, such as the ones shown below.

A Ga⁺ beam is scanned across the surface of a sample, sputtering away material exposed to the beam. Conical shapes are easily obtained using ion milling, enabling the preparation of needle-shaped samples suitable for APT.
The optimum resolution for imaging during milling is obtained by using a high acceleration voltage (e.g. 30kV) and low ion current (30 pA). However, it is recommended to work at lower ion energies during the final stages of APT sample preparation, to limit ion beam damage. The final stages of APT sample preparation with FIB involve annular milling, enabling the formation of a tip with an even radius.

FIB can be used on an electropolished sample in order to position a feature of interest within the tip. This method is quick and easy, but can only be used for conductive materials (suitable to be electropolished) that have a sufficiently high density of the feature of interest (usually grain boundaries).

Another method uses a thin wedge, typically obtained by tripod polishing. The wedge is attached to a support grid and material is removed using FIB, to produce one or more ~ 4 µm wide posts. APT tips are then sharpened using annular milling.

Most FIB systems can also be used to deposit material onto the surface of the sample. A precursor gas is delivered to the surface region of the sample. When explosed to the ion beam (or electron beam), the gas decomposes into a solid material, allowing deposition onto specific areas of the surface of the sample. A typical gas source used for deposition contains platinum (Pt). Deposition of Pt onto the sample surface can be used to protect a beam-sensitive region of interest or to attach small samples to a micro-manipulator within the instrument chamber.

To perform the FIB lift-out technique, a wedge is first cut from the sample and attached to a micromanipulator needle using Pt-deposition. Pieces of this wedge are then milled and welded to a support structure (typically electropolished metal grids or a commercial micro-tip array) by using ion beam assisted Pt-deposition. The sample is then milled to form a needle shape. The final milling uses annular patterns to form an APT tip with a typical diameter of ~100 nm. All of the steps involved in this lifout technique can be seen in the sequence of images below.

FIB techniques are now routinely used for APT sample preparation and thanks to improved instrumentation and methods, the quality and consistency of specimens prepared by FIB is very high.