Applications of a position-sensitive atom probe in rare metals studies

This paper reviews a new development in the experimental technique for atom probe microanalysis. In the position-sensitive atom probe (POSAP), mass spectrometry using time-of flight is combined with position sensing with a wedge-and-strip detector. This not only produces a chemical analysis from a larger area on the specimen, but also allows the position of impact of each field-evaporated ion to be determined. Since atom probe analysis is a depth profiling technique, successive atomic layers removed from the specimen surface are analysed, permitting 3-dimensional reconstruction of atomic scale chemistry. The applications of the position-sensitive atom probe are illustrated, including the studies of spinodal decomposition in an Fe-Cr alloy, precipitation in an aluminium alloy, heterostructures in a III-V GaInAs-InP quantum well compound semiconductor and surface segregation in a YBaCuO ceramic oxide superconductor.