Local magnification effects related to the presence of a second phase in three-dimensional atom probe have been investigated using a simulation of ion trajectories from the analyzed sample surface. Spherical precipitates containing 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 (EB) was varied from 1.15 EA to 0.85 EA. The trajectories were found to overlap over distances close to 1 nm only when the reduced evaporation field (εB=EB/EA) is outside of a gap ranging from 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 case for particles which have a diameter larger than a critical value of 2 nm.
A delay-line position-sensitive detector with improved performance is presented. In this device, timing is carried out by means of fast digitizer boards. The use of dedicated signal processing procedures leads to a timing accuracy of 70 ps and a dead-time below 1.5 ns. As a result, the spatial resolving power of this detector is close to 1 mm leading to a high multihit capability. A temporary detector has been designed in which the delay-line anode is combined with a phosphor screen allowing additional positioning to be made via a charge-coupled device camera. This additional positioning is used to unambiguously quantify performances in terms of spatial resolution and multihit capabilities. A three-dimensional atom probe analysis of a material containing low evaporation field phases is used to demonstrate the capabilities of this detector.
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