Invited Lecture

Christoph FREYSOLDT (MPIE, Düsseldorf)

Towards a quantitative theory of field evaporation 

Field evaporation, i.e., the combined ionization and release of atoms from a surface under the influence of an extreme electric field, is the elementary step at the core of the atom probe. Ultimately, the details of this process determine how well we can reconstruct the original location of ions that hit the detector. Yet our understanding has many gaps. At which field do atoms evaporate from an alloy or a compound? How far can atoms move before leaving the surface? What determines the size and charge of compound ions? The standard theory found in textbooks considers highly idealized situations that neglect most details of a real surface, such as the local configuration, the type of bonds, alloying effects, etc. To arrive at a more quantitative picture of the field evaporation process, the field-induced bond-breaking can be investigated with modern electronic-structure methods such as density-functional theory. I will give an overview over key aspects of the modern theory of field evaporation at the atomic scale, and the various qualitative features that result in measurable distortions of the detector signal. I will notably touch upon the field-dependence of thermal evaporation barriers, roll-over, and the interplay of chemical and structural effects.