Tomographic atom probe: New dimension in materials analysis

Materials science requires the use of increasingly powerful tools in materi als 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 tomograp hic atom probe (TAP) is a three-dimensional atom-probe (3-DAP) developed at the University of Rouen. In this instrument, the specimen is field evapora ted, 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 wit hin each field-evaporated layer on a nearly atomic scale. After analysis, t he 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-DA P is its single-atom sensitivity and very high spatial resolution. In addit ion to 3-D visual information on chemical heterogeneity, 3-D images give an accurate measurement of the composition of any feature without any convolu tion bias. This study first describes the history of the 3-DAP technique. I ts main features and the latest developments of the TAP are then detailed. The performance of this instrument is illustrated through two recent applic ations in materials science. Possible ways to further improve the technique are also discussed.