A model accounting for spatial overlaps in 3D atom-probe microscopy

The spatial resolution of three-dimensional atom probe is known to be mainl y controlled by the aberrations of ion trajectories near the specimen surfa ce. An analytical model accounting for the spatial overlaps that occur near phase interfaces is described. This model makes it possible to correct the apparent composition of small spherical precipitates in order to determine the true composition. The prediction of the overlap rate as a function of the particle size was found in remarkably good agreement with the simulatio ns of ion trajectories that were made. The thickness of the mixed zone arou nd beta precipitates was found to be of 0.3 nm for a normalised evaporation field of beta phase of 0.8. Using simulations, the overlap rate could be p arameterised as a function of the apparent atomic density observed in parti cles. This model has been applied to copper precipitation in FeCu. (C) 2001 Elsevier Science B.V. All rights reserved.