Trajectory overlaps and local magnification in three-dimensional atom probe

Local magnification effects related to the presence of a second phase in th ree-dimensional atom probe have been investigated using a simulation of ion trajectories from the analyzed sample surface. Spherical precipitates cont aining only B atoms embedded in pure A solid solution were considered. The magnification was found to vary drastically from 0.5 to 2.0 times when the evaporation field of B (E-B) was varied from 1.15 E-A to 0.85 E-A. The traj ectories were found to overlap over distances close to 1 nm only when the r educed evaporation field (epsilon(B)=E-B/E-A) is outside of a gap ranging f rom 0.9 to 1.1. Simulations indicate that the "measured" composition in the inner core of precipitates is not biased in this gap. This is also the cas e for particles which have a diameter larger than a critical value of 2 nm. (C) 2000 American Institute of Physics. [S0003- 6951(00)01021-4].