Chapter Three - Basics of Field Ion Microscopy

Abstract

Field ion microscopy (FIM) is historically the ancestor of atom probe tomography (APT). Under the guidance of E. Müller, it evolved from a theoretical concept to the first ever instrument to allow mankind to observe individual atoms. In October 1956, a metal surface was observed with true atomic resolution. From this day, it is used to observe mostly metal, but also some semiconductors, when atomic resolution is needed. It proved to be a powerful instrument, revealing the atomic structure of dislocation or grain boundaries. It also allows the observation of second phase particles, bringing information related to size, shape, volume fraction, etc. More recently, its three-dimensional (3D) version provides atomically resolved 3D reconstructions. Because FIM only provides “black and white” micrographs, with almost no chemical information, the next step was the introduction of atom probe. Nowadays, APT provides at the end a 3D map of the atoms defined by their positions and their elemental natures. One could think that using FIM would therefore be superfluous. But FIM shares most of its physical principles with APT, and it is important to keep in mind that what is observed in a FIM micrograph is not strictly an image of the surface, but rather an image of the electric field present above the surface. Seeing this distribution gives access to key parameters for understanding and calibrating APT images from the same sample. In addition, its unparalleled spatial resolution is, in most cases, better than what can be achieved by APT. Coupled to chemically resolved APT images, FIM offers always an invaluable way to provide structural information in material research. This chapter describes the basic principles of FIM starting from the basic hypotheses of the emission process. Various illustrations of the capability of FIM in material science will be presented, discussing its limits and the possible artifacts for different classes of materials, from pure metals to complex heterogeneous nanomaterials.