Atom probe tomography (APT) is a characterization technique of material enabling the investigation of matter at the atomic scale. This instrument enables the three dimensional (3D) reconstruction of the organization of atoms in a small volume from a solid sample, which justifies why this instrument is increasingly used in more and more fields of research. Initially dedicated to metallurgy, applications of this technique are nowadays numerous in micro- and nano-electronics and applications are also now opened to other fields like biology, or geoscience. This instrument is commercially available (the latest generation, the LEAP 5000 was developed by CAMECA inc.) and is routinely used in about 50 laboratories all around the world.
The ancestor of APT is the field ion microscope (FIM) developed in the fifties by Prof. E.W. Müller. APT shares with FIM the basic principles of field-induced emission from a sample prepared as a sharply pointed needle. This technique was the first to give an image of individual atoms decades before electron microscopy or scanning tunneling microscopy. Since the first generation of FIM, atom probe has experienced several revolutions during about 60 years of development. In 1967, atom probe field ion microscope (APFIM) was developed by Müller and Panitz at Pennsylvania State University. The FIM, that was an atomic scale surface visualization technique, was turned into a nano-analyzing technique. The major breakthrough in APFIM is the elemental identification of atoms observed at the surface of sample imaged in the FIM by using time-of-flight mass spectrometry (ToF-MS). Some years later, John Panitz developed the predecessor of atom probe tomography, named imaging atom probe (IAP). It could record the positions of a single elemental species on the whole surface of the observed sample by using a spherical microchannel plate amplifier centered on the specimen apex, transforming the 1D nature of atom probe into a 2D mapping technique. One step further was the first generation of 3D atom probe, developed at the University of Oxford by adding a 2D position sensitive detector to a standard atom probe and using a graphic workstation to reconstruct and explore 3D map of atomic positions deduced from analyses with this instrument. Improvements in detection capabilities and accuracy of the reconstruction algorithms by Blavette and co-workers opened the atom probe tomography to the panel of indispensable techniques for the nano-analysis of metals and alloys. The advent of local electrodes, laser pulsing, and focused ion beam milling for the preparation of samples, opened the range of applications of this technique to various kind of semiconductors, insulators, and some organic materials, .