Three-dimensional imaging of chemical order with the tomographic atom-probe

The tomographic atom-probe (TAP) is a high-resolution nanoanalytical microscope, recently developed in our laboratory, which provides three-dimensional maps of chemical heterogeneities in a metallic material on a near-atomic scale. The basic principle of this new generation of apparatus relies on the field evaporation and ionisation of atoms from the material. Chemical species are identified by time-of-flight mass spectrometry. The position of atoms at the specimen surface is determined with the aid of a specially designed position-sensitive multidetector. In this paper, application of the TAP to long-range order in intermetallics is discussed and illustrated through various examples (FeAl B2 structure, L12-ordered precipitates in nickel-based alloys). Thanks to its very high depth resolution, better than 0.1 nm, this new generation of analytical microscope is able to map out the chemical order field in alloys.