The distribution of small amounts of alloying elements or impurities to interfaces can have a major influence on the properties of a material and the atom probe field ion microscope technique is well suited for the study of such segregation effects, where structural and compositional changes often take place over regions only a few nanometers wide.

Many features of the atom probe technique make it very useful in studies of interfaces:

1. i) high spatial resolution, about lnm laterally and 0.2 nm in depth

2. ii) equal sensitivity for all elements, including the lightest

3. iii) no specimen contamination, surface artifacts from the specimen preparation are removed by field evaporation,

4. iv) low temperature operation, negligible diffusion during analysis

A ncessary prerequisite for any systematic analysis is the ability to prepare suitable specimens. The volume accessible for analysis by APFIM is orders of magnitude smaller than a typical grain size, so a specimen preparation technique was developed that could bring features of interest sufficiently close to the apex (see Fig. la).