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 (FeAI B2 structure, Ll(2)-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. (C) 1998 Published by Elsevier Science B.V. All rights reserved.