Spatial Resolution in the Atom Probe Field Ion Microscope

Abstract

The atom probe field ion microscope can resolve and identify individual atoms. This ability is demonstrated in a pair of field ion micrographs of an Ni3Al specimen, Fig. 1, in which the individual atoms on the close packed (111) plane are clearly resolved. Comparison of these two micrographs reveals that an individual atom was field evaporated between the micrographs. Due to the hemispherical nature of the specimen, the ability to resolve this two dimensional atomic arrangement is only possible on low index plane facets. The spatial resolution in field ion images is determined by a number of factors including specimen temperature, material, microstructural features, specimen geometry, and crystallographic location.The spatial resolution of the data obtained in atom probe and 3 dimensional atom probe compositional analyses can be evaluated with the use of field evaporation or field desorption images. The field evaporation images are formed from the surface atoms with the use of a single atom sensitive detector whereas the field ion image is formed from the projection of a continuous supply of ionized image gas atoms.