Materials science requires the use of increasingly
powerful tools in materials analysis. The last 20 years have witnessed
the development of a number of analytical techniques. However, among
these techniques, only a few allow observation and analysis of
materials at the nanometer level. The tomographic atom probe (TAP) is a
three-dimensional atom-probe (3-DAP) developed at the University of
Rouen. In this instrument, the specimen is field evaporated, atomic
layer by atomic layer, and the use of a position-sensing system makes
it possible to map out the chemical identity of individual atoms within
each field-evaporated layer on a nearly atomic scale. After analysis,
the volume of matter removed from the specimen can be reconstructed
atom by atom in the three dimensions of real space. The main advantages
of the 3-DAP is its single-atom sensitivity and very high spatial
resolution. In addition to 3-D visual information on chemical
heterogeneity, 3-D images give an accurate measurement of the
composition of any feature without any convolution bias. This study
first describes the history of the 3-DAP technique. Its main features
and the latest developments of the TAP are then detailed. The
performance of this instrument is illustrated through two recent
applications in materials science. Possible ways to further improve the
technique are also discussed.