Atom Probe Tomography
Résumé
A main goal of atom probe tomography (APT) is to provide three-dimensional reconstruction of a material wherein the location of atoms is displayed together with the nature of chemical species. The material is prepared as a short tip with a curvature radius close to 50 nm. Atoms from the surface are field evaporated by combining direct current voltage and voltage or laser pulses. XY position and timing information of each evaporated atom are measured on particle-sensitive detection systems. This gives access to the original position of the atom in the tip and its chemical nature by time-of-flight mass spectrometry. The quality and accuracy of data obtained with APT depend on the intrinsic performances of the detection system used to collect ions during the analysis. To understand the key role of the detection system, the various mechanisms linked to the evaporation field and their influence on the timing and two-dimensional positioning information are considered. The definitions of coevaporation, mass and spatial resolving powers, and mass and spatial resolutions are provided. The influence of atom probe geometry on these parameters is also considered. Different original solutions used to develop detection systems are presented, with special emphasis on standard and advanced delay line detectors.