Microscopy and Microanalysis

Analysis of Three-dimensional Atom-probe Data by the Proximity Histogram

Olof C.  Hellman  a1, Justin A.  Vandenbroucke  a1, Jörg  Rüsing  a1, Dieter  Isheim  a1 and David N.  Seidman  a1
a1 Department of Materials Science and Engineering, Northwestern U niversity, 2225 N. Campus Drive, Evanston, IL 60208-3108

The three-dimensional (3D) atom-probe tech nique produces a reconstruction of the elemental chemical identities and three-di mensional positions of atoms field evaporated from a sharply pointed metal specim en, with a local radius of curvature of less than 50 nm. The number of atoms coll ected can be on the order of one million, representing an analysis volume of appr oximately 20 nm × 20 nm × 200 nm (80,000 nm3). This large amount of data allows for the identification of microstructural features in a sam ple, such as grain or heterophase boundaries, if the feature density is large eno ugh. Correlation of the measured atomic positions with these identified features results in an atom-by-atom description of the chemical environment of crystallogr aphic defects. This article outlines a data compilation technique for the generat ion of composition profiles in the vicinity of interfaces in a geometrically inde pendent way. This approach is applied to quantitative determination of interfacia l segregation of silver at a MgO/Cu(Ag) heterophase interface.