FIB Chemical Contrast
Both focused ion beam secondary electron (SE) and secondary ion (SI) images exhibit chemical contrast. The contrast in SE images, however, is much less interpretable than SEM BSE images because FIB contrast is not substantially related to atomic number. In certain cases, FIB SI images show greatly enhanced chemical contrast which is readily interpretable, such as in the presence of oxygen at the grain boundaries of metallic samples.
The image (right) shows FIB secondary ion imaging of a nickel based superalloy exhibiting grain boundary corrosion, an intergranular attack in Ni-based Alloy 600.
Note that the grain boundary corrosion is highlighted in FIB secondary ion imaging mode due to the significantly enhanced secondary ion yield of a metal in the presence of oxygen.